Organic semiconductors are an emerging class of materials with various optoelectronic applications and huge potential in supporting the development of greener electronics.In my talk, I will introduce sustainable routes to manufacture solution-processed organic photovoltaics. Most organic electronic devices are fabricated from halogenated and non-halogenated aromatic solvents, primarily due to the good solubility of the materials in the solvents and the ideal microstructure/crystallinity they are forming in those. For large-scale production and further commercialisation, this is a key limitation, as they can be carcinogenic or toxic to the human reproductive systems and negatively impact the environment. Here, I will show high-performing organic solar cells developed from novel, more sustainable organic semiconductors (in terms of less waste during synthesis and less energy consumption) as well as eco-friendly solvents. In particular, solvents derived from biomass have been explored for their application in delivering high-performing organic photovoltaics based on PTQ10:Y12 and FO6-T:Y12 with PCE > 14%.

Finally, I will discuss possible degradation mechanisms of the bulk heterojunction systems containing Y6 or Y12 as the acceptor, after degradation with indoor and outdoor light. A combination of electrical, morphological, and spectroscopic techniques were used to evaluate the degradation pathways of the OPVs.  

The rapid expansion of the Internet-of-Things (IoT) is driving the demand for energy-autonomous devices. With billions of wireless sensors expected to be installed in indoor environments over the next decade, battery usage in IoT is growing, leading to higher management costs and waste. Indoor photovoltaics (IPVs) offer a sustainable power solution by reducing battery waste. [1] Air-stable perovskite-inspired materials (PIMs) are promising low-toxicity semiconductors with wide bandgaps (1.8–2.0 eV) for efficient indoor light harvesting, with theoretical IPV efficiencies approaching 40% or more. However, the inherent low-dimensional nature of PIMs and high defect densities pose challenges, such as carrier localization, in achieving very high IPV efficiencies. [2]

In this talk, I will present our recent results on two-dimensional PIMs comprising Group VA pnictogen cations, such as antimony (III) (Sb³⁺) and bismuth (III) (Bi³⁺). Through thorough compositional engineering at each crystallographic site (A, B, X) of the PIM structure, we achieved the highest indoor power conversion efficiency for IPVs based on halide PIMs. [3-5]  Notably, the IPV devices of Cs₂AgBi₂I₉ PIM maintained consistent performance under different light color temperatures, demonstrating the versatility of Cs₂AgBi₂I₉ as a reliable IPV absorber in various indoor environments. Our research paves the way for sustainable indoor light harvesting by identifying or developing 2D pnictogen-based PIMs with adaptable structural and photophysical properties.

The potential of perovskite-based photovoltaics is rapidly becoming recognised as a probable and significant contributor towards attaining climate neutrality by 2050. Indeed, perovskites highly tuneable optoelectronic properties coupled to its facile, low-cost and scalable fabrication allow for a wide variety of innovative applications such as tandem configurations (silicon-perovskite or perovskite-perovskite), space applications due to their high power-to-weight ratio and even indoor light harvesting. [1] Whilst most of the attention is being put towards maximizing performance, critical sustainability aspects are often being overlooked. Indeed, the sustainability of these devices should also be at the forefront of development in order for this emerging technology to be commercialized and accepted by the market, allowing for its widespread deployment.

In the last 10 years, Perovskite Solar Cells (PSCs) have experienced a meteoritic rise in performance, arriving most recently at 26.1% power conversion efficiency, (PCE) directly competing with silicon-based photovoltaics. [2] Nevertheless, comprehensive solutions on reducing the environmental impact of the device are still lacking in literature. More specifically, high performing devices are still manufactured with materials that require, out of necessity, toxic and environmentally damaging solvents that could pose a threat towards the ambient-air, large-scale (e.g. Roll-to-Roll) manufacturing aspects. [3] Furthermore, the use of critical raw materials [4] is still highly favoured (i.e dopants), discouraging the technology impact at a larger scale. Finally, materials employed in the cell (e.g. organic hole transport layers (HTL)) are usually very expensive due to their lengthy and inefficient synthetic and purification procedures, resulting in no technology readiness levels (TRL) associated for TW levels of production. [5]

To help fill the research gap between sustainability and performance, we developed an array of cheap, novel HTL layers, based on the state-of-the-art poly(triarylamine) (PTAA) [6], that can be processable in “greener” solvents. This was achieved by the modification of the triphenylamine polymeric backbone via the incorporation of a phenothiazine organic scaffold, which shows good solubility in common organic solvents. [7] Additionally, the methyl substitution of the TPA phenyl unit was modified to evaluate the trade-off effect on solubility and performance. An additional benzothiadiazole unit was also included due to its promising nature in organic semiconductors. [8]

The resulting polymers presented good solubility in our proposed, more sustainable solvent: tetrahydrofuran (THF) that is non-aromatic, non-halogenated, cheap, has a low environmental risk and a low human health toxicity. [9] A full structural, optoelectronic, and thermal characterization resulted in polymeric compounds P1-4 that displayed suitable HTL properties. These were then applied to flexible n-i-p devices with PTAA as the reference. One of the polymers (P1) revealed competitive efficiencies when PTAA is deposited using toluene (conventionally used in literature) and even outperforms the reference when processed with THF. P1 also displayed a remarkable enhancement in unencapsulated light soaking stability, with respect to PTAA devices. A solid-state film analysis allowed us to determine that the synthetic tailoring of structural components is key for performance enhancement.

Following on from this, a doping optimization was also conducted using multi-variate analysis approach (i.e. Design of Experiment), aiming at obtaining the right combination of HTL and dopant concentrations, resulting in enhanced PCEs with a better efficacy in material use. Finally, a thoughtful revisit of the synthetic protocols was considered targeting innovation and more eco-friendly processes. In fact, we were able to substitute conventional organic solvent procedures that are lengthy, generate waste, typically low to moderate yielding and employ high temperatures, to protocols employing more sustainable and recyclable mediums (i.e. water), permitting for reactions that are very high yielding, selective, fast and above all, scalable, simple, low-cost and can progress to higher TRL levels.

Indoor photovoltaics (IPV) is increasing the scientific interest due to the expected internet of things (IoT) market increase, doubling its size by 2030. IPV can be used as a sustainable energy supply for sensors and low consumption applications, as an alternative to batteries. Thus, reducing the need of replacement and the amount of waste generated along the lifetime of the devices. Research is ongoing to improve relevant materials and devices for this application, focusing in indoor (inside of buildings) environments. In this sense, organic photovoltaics (OPV) is an interesting alternative due to the bandgap tuning of these materials, their high absorption in thin layers and their good performances (>30%[1,2]) already demonstrated under low illumination. Furthermore, the possibility of using more sustainable processes: printing in air with short high temperature steps; meaning lower energy consumption and cost than other PV technologies. Positioning IOPV as an alternative for this application.

IOPV creates a new field of application with strong differences compared to outdoor applications. First, illumination in indoor is based on fluorescent or LED lamps with different color temperatures, so absorption needs to be tuned to the visible region considering the emission spectra of those different lamps. Second, devices need to be performant at low illumination (200-1000lux). These requirements need device optimizations using material choices that reduce defect-driven recombination in the different layers of the devices. Meaning that, in order to improve their performance (PCE) at low illuminances, a high open-circuit current and low shunt resistance are required. Further, a good compromise of low series resistance (depending on the device behavior at low illumination) is required. Finally, stress factors in indoor operation conditions are milder than outdoor, being a favorable scenario for the use of OPV devices. However, research is still needed to investigate the stability of indoor cells and modules [3].

In the IOPV-Lab, the common laboratory between CINaM, IM2NP and the company Dracula Technologies we are working on an OPV blend system based in non-halogenated solvents processed in air with PCEs over 20% at low illumination. We are also studying the ageing behavior of this system, trying to understand the impact of cosolvent and additives utilization on their stability under combined indoor conditions. This study may allow us to understand if the devices are stable under operation for IoT applications in the long term. First tests seem to show that the most performant formulation is not stable after ageing, so a detailed study is ongoing to proof the formulation variability on the stability of the device. Opening up an alternative non-halogenated formulation that represents a suitable option for IOPV devices

IOPV samples have been fabricated in air by doctor-blade coating (with a final evaporation step), as scalable technique for industrial transfer. Samples have been characterized in different indoor conditions and illumination ranges before and after encapsulation. Then, an “indoor ageing test”, which includes temperature, humidity and indoor lighting conditions, is ongoing to check the interaction of the different stress-factors under real degradation conditions. Further, different optical (such as absorbance), opto-electronical (IV, EQE, LBIC, …) and morphological characterization methods are used at different times of the ageing test to understand the stability behavior of the different sample types. Results are expected to give us an overview of the best combination of solvent/cosolvent + additive in terms of stability.

The oral presentation expects to give an overview about indoor applications field and to present the best results of the studied system. It will include the stability using different non-halogenated formulations and using scalable techniques. Thus, providing valuable information of the real feasibility of IOPV devices use for indoor-PV applications.

We present an isolated plasma soft deposition (IPSD) technique for the plasma damage-free deposition of an amorphous InGaTiO (IGTO) top cathode on semi-transparent perovskite solar cells (PSCs). Unlike conventional DC or RF magnetron sputtering, where plasma directly faces the target, the IPSD process utilizes an isolated plasma region that prevents plasma irradiation, ensuring the deposition of the IGTO cathode without damaging the soft perovskite active layer. The confinement of high-density plasma in isolated regions, achieved through a Nd-Fe-B45 magnet array, further protects the active layer by minimizing the impact of energetic particles from the sputtered IGTO targets. Additionally, linear scanning of the glass substrate within this isolated plasma region enables low-temperature, large-area IGTO deposition. Under optimal conditions, the IPSD-processed IGTO film, with a thickness of 150 nm, exhibited a low sheet resistance of 31 Ω/square, high average optical transmittance of 91.41%, and a work function of 4.1–4.5 eV. To demonstrate the feasibility of this technique, we fabricated semi-transparent PSCs with spin-coated perovskite layers. The PSCs with IPSD-processed IGTO cathodes achieved a power conversion efficiency (PCE) of 17.52%, comparable to the 4.35% PCE of PSCs with magnetron-sputtered ITO cathodes, due to the absence of plasma-induced damage. Furthermore, we successfully integrated the IPSD technique into the fabrication of PSC and Si-based tandem solar cells, achieving PCEs ranging from 24% to 28%. These results highlight the significant potential of the IPSD-based deposition process as a key technology for the commercialization of semi-transparent PSCs and tandem solar cells.

To achieve higher electricity generation at a low cost, the most substantial impact on the energy generation from solar cells is to make existing technologies more efficient per area. This forms the focus of tandem solar cells, which utilize different photoactive materials with different bandgaps, allowing benefiting from a broader range of the solar spectrum. Recent advances in perovskites have dramatically improved their efficiency, with tandem devices—particularly those using silicon bottom cells—showing great potential for further performance enhancement. However, the phase instability of wide-bandgap perovskite top cells under prolonged operational conditions, including exposure to light and heat, poses a significant challenge. To solve the issue, different approaches will be discussed; grain boundary, bulk of perovskite, and the interfaces with charge transport layers. For example, recently, we addressed this by improving cation interactions within the perovskite lattice, enhancing phase stability under light and heat. Furthermore, improving the optical properties and reducing recombination losses has been key to achieving a certified efficiency of 33.7% in perovskite-silicon tandem cells, demonstrating both enhanced performance and operational durability. I will discuss how we are addressing these challenges, utilizing optical spectroscopy and comprehensive analysis techniques.

Over the past decade, substantial strides have been made in enhancing the performance of tandem cells, culminating in dual junction configurations achieving PCEs nearing 34%, marked by various record-breaking updates.[1] In 2023, our research contributed significantly to this progress, unveiling three PCE records of 32.5%, 33.2%, and 33.7%.[2] These achievements were made possible by introducing solution-processed perovskites on micron-sized pyramidally textured c-Si bottom cells and a series of improvements at the interfaces and the bulk of the perovskite. As for the interfaces, we had to solve several issues, such as introducing a dielectric interlayer between perovskite and fullerene contacts to mitigate induced defect states [3], enhancing the recombination junction through ultrathin indium zinc oxide electrodes, introducing alternative hole selective contacts including polymers,[4] nickel oxide,[5] and self-assembled monolayers, and using alternative transparent electrodes. Each step of these advancements and their corresponding stability assessments revealed the pivotal role of interfaces. We also discovered that interfaces play a crucial role even during the encapsulation process, as thermomechanical stresses drive the degradation of solar cells, making interfacial strengths critically important. Furthermore, from a sustainability perspective, reducing the use of critical elements on the contacts is essential. To address this, we minimized the use of indium in the transparent electrodes of our tandem solar cells, thereby enhancing light coupling in the devices and making the process more sustainable [6]. Despite the remarkable achievements in perovskite-silicon tandem solar cells, their use in space remains a concern due to the radiation sensitivity of the silicon heterojunction bottom cells, while other extremes are still yet to be demonstrated. In this invited talk, I will present our systematic solutions to solve stability issues in dual junction tandem solar cells, along with insights into their potential for space applications.

The field of photovoltaic (PV) technologies is undergoing a rapid transformation, driven by the demand for high efficiency, cost-effective, and scalable solutions. Emerging PV materials, including perovskites, organic photovoltaics (OPVs), and tandem architectures, are pushing the boundaries of efficiency and stability, with record-breaking power conversion efficiencies (PCE) now at 27% for single-junction perovskites and surpassing 34% in perovskite-silicon tandems. The industry is shifting towards scalable fabrication techniques such as blade coating, slot-die printing, and vapor deposition to enable large-area, high-throughput production while maintaining performance. A key focus in the field is the improvement of long-term stability, as operational lifetimes continue to be a primary barrier to commercialization. Advances in encapsulation, interfacial engineering, and composition tuning have significantly enhanced the durability of next-generation PVs, with stability benchmarks extending beyond 1,000 hours under accelerated aging tests. Additionally, flexible and lightweight PVs are gaining momentum, enabling applications in portable electronics, wearable technology, and building-integrated photovoltaics (BIPV). Mechanical resilience, particularly in thin-film and flexible devices, is becoming a crucial parameter, alongside efficiency and environmental stability. The integration of artificial intelligence (AI) and automation in material discovery and device optimization is also accelerating innovation, allowing for rapid screening of new compositions and processing conditions. As research continues to bridge the gap between laboratory-scale performance and real-world implementation, the standardization of testing methodologies and upscaling strategies will be critical in determining the commercial viability of emerging PVs. The ongoing advancements in materials science, device engineering, and manufacturing technologies position photovoltaics at the forefront of the renewable energy transition, paving the way for next-generation solar energy solutions.

Flexible perovskite solar cells (f-PSCs) have the potential to revolutionize various applications, including IoT, portable and wearable electronics, and space technology, where flexibility, conformability, lightweight design, and a high power-to-weight ratio are highly desirable. In addition to their impressive efficiency (reaching up to 25%[1]) f-PSCs offer several other advantages: they are fabricated using abundant materials through cost-effective solution-based processes [2]. However, even more than their rigid glass counterparts, the long-term stability of f-PSCs remains a challenge due to both intrinsic and extrinsic factors [3]. Effective encapsulation is crucial for ensuring durability by protecting the devices from external elements such as moisture, water, and oxygen, without compromising their flexibility. Thermosetting polyurethanes (PUs) emerge as promising encapsulants due to their chemical inertness toward the perovskite layer and their ability to cure at room temperature directly on the PSC [4]. Additionally, minor structural modifications in PU precursors can enhance flexibility, barrier properties, and transparency. This study demonstrates the successful use of a low-cost thermosetting PU resin for encapsulating 1 cm² f-PSCs. Two encapsulation approaches were explored: one where PU is applied solely to the back (in contact with the metal electrode) and another where PU is applied to both the back and the front (on the PET substrate). While maintaining device flexibility as proved by bending tests, the dual-layer encapsulation strategy significantly improves stability under high humidity conditions (relative humidity >75%), achieving a T₈₀ lifetime of over 550 hours (23 days). This represents a substantial improvement compared to unencapsulated devices, which exhibit a T₈₀ of only 6 hours.

Perovskites face significant stability challenges arising from both extrinsic factors like humidity and intrinsic issues linked to their ionic nature. These stability limitations hinder the long-term performance of perovskite-based devices. Mastering crystallization processes, whether in thin films or bulk, is a critical step in overcoming these obstacles. High-quality, highly crystalline materials are essential not only for enhanced stability but also for reliable characterization, which is key to understanding the mechanisms governing device operation. 

Monocrystalline perovskites offer a compelling alternative to conventional thin films, benefiting from the absence of grain boundaries and their associated defects. Achieving these high-quality materials demands precise control over synthesis methods to improve both material properties and stability. 

In this contribution, we will explore diverse synthesis approaches for perovskite single crystals, including the widely used inverse temperature crystallization (ITC) with seed-assisted growth, adaptations for multi-halide-core crystals and confined-growth methods. We will also introduce two innovative techniques: a continuous-flow reactor for large-scale crystal growth and a novel dry synthesis methodology for narrow-bandgap perovskites. 

Furthermore, we will present advanced and non-conventional characterization techniques applicable to these materials, both as stand-alone crystals and in optoelectronic devices. Finally, we will demonstrate the remarkable stability of high-crystallinity perovskite single crystals, including their performance under extreme conditions such as gamma radiation, highlighting their potential for space applications. 

Perovskite solar cells (PSCs) have attracted intensive attention due to their ever-increasing power conversion efficiency (PCE), low-cost materials constituents, and simple solution fabrication process. In printable mesoscopic PSCs, the perovskite is deposited on a triple-layer scaffold, made of screen printed mesoporous TiO₂ layer, ZrO₂ spacer layer and carbon electrode; such devices use carbon electrodes to replace the noble metal back contacts and do not require a hole-conducting layer.

Controlling the crystallization of organic–inorganic hybrid perovskite is of vital importance to achieve high performing perovskite solar cells. The growth mechanism of perovskites has been intensively studied in devices with planar structures and traditional structures. However, for the printable mesoscopic perovskite solar cells, it is difficult to study the crystallization mechanism of perovskite owing to the complicated mesoporous structure. In this talk, I am going to share the development of the printable mesoscopic PSCs and how we manage to control the crystallization in mesopores.

The commercialisation of perovskite photovoltaic (PV) technologies requires advancements in large-area module efficiency, scalable and cost-effective manufacturing, and long-term operational stability. Stability issues in perovskite solar cells (PSCs) often stem from the materials used in the hole-transporting layer (HTL). Innovative, sustainable, and affordable hole-transport materials (HTMs) are crucial to address these challenges. Cu₂ZnSnS₄ (CZTS), an earth-abundant p-type semiconductor traditionally used as a light-absorbing material in heterojunction solar cells, has recently gained attention as an HTL for PSCs due to its desirable electronic properties.

This study explores the synthesis and application of CZTS nanoparticles (NPs) as an HTM in PSCs. The nanoparticles were produced using a hot-injection method under an oxygen-free environment and subsequently processed into an ink formulation for spin-coating. The resulting CZTS thin films, approximately 50 nm thick, were annealed to ensure structural and optical transparency in the visible solar spectrum. Comprehensive material characterisation—including transmittance, Raman spectroscopy, UV-Vis spectroscopy, scanning electron microscopy, and X-ray diffraction—confirmed the quality and stability of the CZTS layers.

Preliminary findings indicate that PSCs employing CZTS as an HTL demonstrate superior stability compared to conventional organic HTM devices. Over one month, the CZTS-based devices retained or even improved their photovoltaic efficiency, unlike organic HTL-based devices, which experienced significant degradation. Current-voltage measurements, external quantum efficiency and photoluminescence spectroscopy analyses revealed enhanced charge injection in the CZTS HTL. These results suggest that CZTS is a robust and sustainable alternative to traditional HTMs, paving the way for more durable perovskite PV technologies.

Perovskite-silicon tandem solar cells offer exceptional promise for high efficiency photovoltaics. However, integrating perovskite top cells uniformly onto textured silicon wafers remains challenging. Physical vapor deposition (PVD) methods, such as pulsed laser deposition (PLD)¹, enable conformal and precise thickness control for perovskite deposition but are underexplored for this application.

Following our work on PLD of MAFAPbI₃ for single junction devices², we discuss two PLD-based approaches towards wide band gap halide perovskites deposited conformally onto texture silicon bottom cells. First, we discuss our recent developments on PLD of Cs_xFA_1-xPb(Br_yI_1-y)₃ films for p-i-n single-junction and monolithic tandem devices. We discuss how the application of a PbI₂-based template results in phase-pure, uniform Cs_xFA_1-xPbI₃ films with dense coverage on both planar and textured substrates. Cs_0.2FA_0.8PbI₃ composition and a bandgap of 1.58 eV are confirmed. By controlling bromide ion incorporation in the PLD target, we achieve tunable bandgap energies (1.58–1.68 eV), aligning with silicon absorbers for current matching.

Additionally, we leverage the conformal properties of PLD, to fabricate inorganic scaffolds of PbI2:CsBr at deposition rates above 50 nm/min. The formation of the Cs_xFA_1-xPb(Br_yI_1-y)₃ perovskite layer is finalised with a spin coating of organic cation solution containing FAI:FABr in ethanol. This also results in uniform films with dense coverage on both planar and textured substrates. Finally, both approaches are compared in terms of device performance, with preliminary results reaching above 13% PCE on 1 cm2 cells and textured silicon bottom substrates. This work highlights the importance of PVD techniques and their optimization for next-generation photovoltaics.

References

1. https://doi.org/10.1021/acsenergylett.4c01466

2. DOI: 10.1016/j.joule.2024.09.001

The development of photovoltaic (PV) technologies based on earth-abundant materials is a cornerstone for sustainable and cost-effective energy generation. Numerous solar-to-X applications, including single junction, indoor, tandem, and semi-transparent PV devices, as well as photoelectrocatalysis, require a broad spectrum of light absorption and band position. This wide variety of solar-driven niche markets necessitates the development of a PV technology with customizable band gaps for specific applications. Mature PV technologies such as crystalline Si, CdTe, and GaAs have fixed bandgap absorbers of 1.1 eV, 1.45 eV, and 1.3 eV, respectively, even though exhibit impressive power conversion efficiencies exceeding 22%. Some emerging PV absorbers like perovskite, organic, and Sb₂(S,Se)₃ also exhibit bandgap tuning properties from 1.2 eV to 1.95 eV, 1.49 eV to 2.0 eV, and 1.2 eV to 1.7 eV, respectively, enhancing the feasibility of tandem solar cell design and other PV applications. However, it is challenging for these materials groups to tune the bandgap below 1.0 eV, limiting the utilization of infrared photons. Moreover, these materials face environmental, cost, and stability concerns, limiting their potential for widespread deployment.

Kesterite semiconductors are gaining attention as they are earth-abundant, nontoxic, and have excellent stability properties and bandgap tuning ability. Recently, this technology has achieved 15% power conversion efficiency using a simple molecular ink process, demonstrating significant potential for widespread deployment. In this work, we will present the high adaptability of solution-based processes to achieve single-phase kesterite materials with high crystalline quality, resulting in devices with efficiencies beyond 10% under AM1.5G, with band gaps ranging from 0.9 to 1.7 eV. A systematic isovalent cationic (Ag, Cd, Ge) substitution for the selenide-based (Cu₂ZnSn(S,Se)₄) and sulfur-based kesterite (Cu₂ZnSnS₄) using advanced molecular ink solutions is the key strategy and will be detailed in the presentation. For the first time, we present a lower bandgap of 0.9 eV kesterite absorber with an efficiency exceeding 12%. A champion device with a 14.4% efficiency kesterite solar cell is achieved with an absorber bandgap of 1.15 eV. Furthermore, we showcase kesterite solar cells with decent efficiency under AM1.5G, with wide bandgaps up to 1.9 eV to 2.2 eV, ideal for indoor and underwater PV applications. Systematic photoluminescent, Time-Resolved Photoluminescence, phase structural, composition, and element distribution analysis, as well as optoelectronic analysis of the device, are performed in this work. This provides valuable insight into reducing recombination in the bulk of the different bandgap absorbers and at the heterojunction interface with different band alignment structures.

Furthermore, two important case studies of bandgap tuning will be presented. Firstly, the performance of the devices in indoor conditions will be measured using a tunable LED solar simulator, to systematically investigate the behavior of wide bandgap kesterite solar cells under a wide range of simulated indoor conditions (from 6000K to 2700K illumination). Over 18% efficiency kesterite solar cells under indoor conditions will be presented. Secondly, the series bandgap-tuned kesterite absorber are used as photocathode for investigating photoelectrochemical properties for water reduction.

In conclusion, this work will demonstrate that the low cost and high tolerance isovalent cationic substitution can lead to a very wide range of bandgap tunability in kesterite absorbers, with their customizable bandgaps enabling them to suit various specific application scenarios. This work provides critical insights into the widespread deployment of kesterite PV technology, offering a roadmap for future advancements.

Metal-organic liquids represent an emerging class of functional materials that combine the unique properties of coordination polymers with the versatility of liquid-state materials. In this work, we present the synthesis and comprehensive characterization of three novel copper-based MOLs and one silver-based MOL, all exhibiting melting temperatures below 100°C. These materials share the same [Cu] backbone structure but achieve different dimensionalities (1D, 2D, and 3D) through variation of the counter-cation, providing an unprecedented opportunity to correlate structural dimensionality with physical-chemical properties. Through detailed thermal analysis, we demonstrate glass transition temperatures ranging from -42°C to -21°C and melting points between 48°C and 88°C. Temperature-dependent Raman spectroscopy reveals the structural evolution during the solid-to-liquid transition, while computational modeling provides insights into the electronic band structures and charge transport mechanisms. The materials exhibit conductivities ranging from 10-10 to 10-6 S cm-1, with dimensionality playing a crucial role in determining transport properties. We demonstrate the practical application of these materials as hole transport materials in dye-sensitized solar cells (DSSCs) without requiring electrolyte additives. The materials' versatility is showcased through successful implementation in three different states - liquid, gel-like, and quasi-solid - offering flexible processing options for device fabrication. This work not only advances the fundamental understanding of metal organic liquids properties and phase transitions but also establishes their potential as multifunctional materials for energy applications.

The widespread deployment of perovskite solar cells (PSCs) or other emergent PV technologies as a sustainable energy solution hinges critically on both their operational stability and the ability to efficiently extract maximum power under real-world illumination conditions. While significant advances have been made in PSC stability, particularly in triple-mesoscopic hole-transport-material-free architectures, conventional maximum power point tracking (MPPT) algorithms fall short when applied to these highly stable but hysteretic devices. This presentation introduces a novel galvanostatic power-tracking algorithm specifically designed to overcome the challenges posed by high-hysteresis PSCs, complemented by comprehensive real-world performance data.

Our approach utilizes cost-effective hardware[1,2] that enables parallel long-term stability measurements, addressing a critical gap in PSC characterization methodology. The system's architecture allows for continuous monitoring and precise power optimization, particularly crucial for devices incorporating power optimizers. We will present detailed performance metrics from extended outdoor testing, demonstrating the algorithm's superior tracking efficiency compared to traditional methods. The real-world data encompasses various environmental conditions, validating the system's robustness and reliability in actual operational scenarios. This work contributes to the broader goal of PSC commercialization by providing a practical solution for accurate power tracking, essential for both research and commercial applications.

Our findings have significant implications for the integration of PSC technology into various applications, including building-integrated photovoltaics (BIPV) and large-scale solar installations, where accurate power optimization is crucial for maximum energy yield. The combination of our innovative tracking methodology and real-world validation data provides valuable insights into the practical implementation of PSC technology, addressing key challenges in stability assessment and performance optimization for sustainable photovoltaic applications.

The rapid development of low-power connected devices, widely used in fields such as the Internet of Things (IoT), building automation, smart agriculture, and wearables, has fueled research into novel technologies that can harvest energy from ambient sources and potentially store this energy, aiming to make these devices energy independent. A significant portion of the billions of IoT smart devices operates indoors, typically powered by batteries that require periodic recharging or disposal. This raises sustainability concerns related to maintenance and electronic waste production, highlighting the need for more efficient and self-sustaining solutions. As a result, there has been increased interest in developing indoor photovoltaics (IPV) for self-rechargeable IoT devices, addressing the limitations of traditional batteries and fostering the growth of large, energy-efficient IoT networks. [1] Moreover, the innovative concept of integrating photovoltaic cells for energy harvesting with an energy storage device, such as a supercapacitor (SC), to directly store this energy in a single unit is gaining recognition as a viable and sustainable alternative to batteries for powering low-power IoT devices. [2],[3] In this contribution, we address the sustainability of such integrated devices by selecting green, sustainable, and low-toxic materials that can be shared between the photovoltaic cell (i.e., a dye-sensitized solar cell, DSSC) and the supercapacitor, with a particular focus on their application in indoor environments. We demonstrate, for the first time, that γ-valerolactone (γ-VL), a sustainable, low-toxic solvent derived from cellulosic biomass, can be used for the preparation of the DSSC electrolyte as an alternative to more common but toxic and flammable solvents such as acetonitrile (ACN) and 3-methoxypropionitrile (MPN). Recently, γ-VL has also been shown to be well-suited for the preparation of high-voltage supercapacitors. [4] Our results indicate that γ-VL is unsuitable for outdoor DSSCs due to slower ion diffusion and reduced I₃^- reduction at the counter electrode. However, γ-VL-based DSSCs outperform those using ACN and MPN under indoor light (1000 lux), demonstrating equivalent short-circuit currents but with higher open-circuit voltages, improved fill factors, and enhanced overall efficiency, enabled by lower recombination at the photoanode. Thanks to the compatibility of γ-VL with both technologies, we fabricated an integrated energy harvesting and storage device using γ-VL for electrolyte preparation. Moreover, we also demonstrate that the same carbon-based materials used for the SC electrodes are also suitable as counter electrodes for the DSSC. The fabricated integrated harvesting and storage device showed optimal self-charging capabilities and stability under indoor illumination conditions, achieving high charging voltage and good charge retention over time, making it a promising alternative to disposable batteries for IoT devices.

Organic solar cells and organic photodetectors have recently gained much interest due to their favorable properties like abundant materials, low-cost fabrication, machanical flexibility, and spectral tunability. In this talk, I will give an overview about our recent work on organic photodetectors. In particular, I will first address results on a key working principle, the exciton separation which is challenging in organic materials due to the high binding energy. We have recently shown that high-performance organic photodetectors can be realized without a needing a donor-acceptor heterojunction for separation: single-component devices based on the small molecule organic semiconductor DCV2-5T (an oligothiophene with dicyano-vinylene endgroups) show excellent properties: Due to low dark current and high external quantum efficiency, high specific detectivities of 10E13 Jones at zero bias are achieved. The single-component DCV absorber layer forms free charges rapidly and efficiently, without the need for a heterostructure with another material. The efficient charge generation in DCV2-5T is attributed to the strong electronic overlap of molecular excitons and intermolecular CT states. Furthermore, quantum chemical simulations predict a reduced electronic coupling for highly ordered (crystalline) DCV2-5T, which demonstrates that crystalline order is not a prerequisite for good performance. The exceptional performance of single-component OPDs demonstrates a successful strategy for simplified device fabrication and enhanced stability. In a second part, I will discuss high-performance narrow-band blue organic photodetectors through intended exciton quenching, realized by fine-tuning the optical and electrical properties of hole transport layers and introducing a MoO3 doped underlayer to the device. This filterless strategy ensures a high EQE of up to 50% at 0 V in thin-film devices. Doping can further improve EQE by assisting charge carrier dissociation. Ultralow dark currents can be obtained by planar heterojunctions, leading to a record-high detectivity D* of 6.35 × 10E14 Jones for blue OPDs, a performance exceeding that of most crystalline inorganic detectors in this wavelength range.