Organic or perovskite photovoltaics poses a multi-objective optimization problem in a
large multi-dimensional parameter space. Massive progress was achieved in developing
methods to accelerate solving such complex optimization tasks. We have demonstrated
for both types of semiconductors, that the combination of Gaussian Process Regression
(GPR) and Bayesian Optimization (BO) are most efficient in predicting new materials,
identify optimized processing conditions or invent alternative device architectures in
larger parameter rooms. For a 4 dim space (solvent, donor-acceptor ratio, spin speed,
concentration) with about 1000 variations in a 10 % grid space, 30 samples are sufficient
to find the optimum. For 6 dimensional spaces, the possible variations go into the
millions and billions. Nevertheless, our automated lines, being operated in an
autonomous optimization mode, were able to identify globalized optima within several
hundred´s of experiments. In the outlook we discuss whether these autonomously
operated research lines can as well handle unorthodox optimization problems such as
the recycling of organic or perovskite solar cells

Narrow bandgap non-fullerene acceptors (NFAs) offer the semitransparency feature that makes organic photovoltaic (OPV) technology attractive for application in niche markets, such as building-integrated photovoltaic and agrivoltaics. However, evaluating each photoactive material system following classical experimentation methodologies and advancing it towards mass production presents a complex multiparametric challenge that requires intensive time and resources. In this talk, we propose the use of high-throughput lateral gradient methodology to evaluate the photovoltaic potential and semitransparency of narrow bandgap material systems.  More than two thousand devices with different narrow bandgap material systems were manufactured using a platform that combines doctor blade coating technique with controllable velocity profiles to create thickness gradients of photoactive layer. As a result, the power conversion efficiency of the blade-coated devices varied between 0.06 to 10.45% in the champion devices of the screened material system. The large data pool collected for all samples was employed to perform statistical analysis to reveal the most influential parameters for narrow bandgap devices. We have found that the electronic descriptors (i.e. electron affinity, ionization energy, and optical band gap) had a more prominent impact on the final device performance than the processing conditions. Finally, we have shown the potential application of each narrow bandgap blend system for semitransparent devices by calculating its average visible transmittance as a function of photoactive layer thickness. Our study paves the way for high-throughput experimentation to accelerate the mass production and materials screening of narrow bandgap OPVs for semitransparent photovoltaic applications.

Semi-transparent organic photovoltaics are potential candidates for making smart windows in buildings and for agrivoltaics. The challenge here is to achieve high light utilization efficiency (LUE) without compromising on average visible transmittance (AVT). In this work, we designed and fabricated selective spectral tuned Distributed Bragg Reflectors (DBR) using alternating layers of TiO₂ and SiO₂, high and low refractive index oxide materials. The reactive sputtered layers on the back side of a pre-coated ITO glass exhibited close to 90% reflection between 650nm to 900nm wavelength range (near infra-red) with an outstanding AVT of around 90%. To test the superiority of these DBR integrated substrates for organic photovoltaics, we first optimized fully slot die coated organic solar cells to achieve above 14% PCE with blend PM6:Y7 systems using an opaque device configuration. Following that, the DBR integrated semi-transparent devices are made with blend PM6:Y7 and AgNWs top transparent electrodes, fully slot die coated. The resulting solar cells show 20% improvement in current density J_sc from the DBR substrates, compared to devices without integrated DBR, and LUE values above 3%, with an AVT around 40% and PCE around 8.3%. These results show the potential of achieving improved semi-transparent photovoltaics with industrial compatible printing processes.

Device modeling is extensively used in solar cell research going from simple models such as the Shockley diode equation or partial differential equations (PDE) to more complex models like Monte-Carlo or drift-diffusion (DD). These models are often used as a diagnostic tool to understand and quantify the main losses for a given device by reproducing experimental measurements.

However, one of the main criticisms about using complex models as a means to quantify material properties is the many fitting (10 to 40) parameters that need to be estimated. Many argue that with so many fitting parameters one could fit almost any model to the experimental data.

In this presentation, the challenges of using high-dimensional physical models to quantify material properties accurately will be addressed. As well as, how machine learning methods such as Bayesian optimization (BO) combined with high-throughput (HT) experimental data can be leveraged to study material properties at scale.

The potential of using modeling, BO and HT data will be illustrated by several case studies using different physical models (PDE or DD) and experimental methods such as (i) transient absorption spectroscopy, (ii) transient photoluminescence and microwave conductivity, (iii) light-intensity-dependent current-voltage characteristics.

The open-source package BOAR (Bayesian Optimization for Automated Research) will be introduced here as a flexible package to address many challenges of solar cell research such as smart experimental planning or fitting of high-dimensional models to experimental data. This package combined with PDE solvers and open-source DD package SIMsalabim provides an easy-to-use and flexible toolbox for solar cell research.

The need of scalable fabrication of high-efficiency organic photovoltaic cells and modules has gradually emerged. In particular, indoor organic photovoltaics (IOPV) constitutes an attractive energy harvesting solution to power IoT devices, given its deployability, reliability, and power density. A substantial portion of the billions of new IoT devices that will be installed in the coming years are expected to be located inside buildings. Such devices like environmental sensors, can have several shapes and sizes, hence the need to develop custom-made conformable photovoltaic devices to facilitate their integration into the final product. In this context, inkjet printing has become a very attracted printing technology for large-scale printed flexible cells and modules with freedom of shapes and designs.

Herein we demonstrate the challenge to go from lab-scale to industrial scale to achieve highly efficient fully inkjet printed IOPV cells and module. To prove the great advantage of inkjet printing as a digital technology allowing freedom of forms and designs, particular OPV modules with different shapes are demonstrated and integrated into different IoT devices to operate autonomously without using batteries or connections to the grid to ensure sufficient flexibility in their placement.

Inverted Organic Photovoltaics (OPVs) allowed more flexibility on designing the roll-to-roll (R2R) production process and thus provided technological opportunities to OPV technology [1,2]. In addition, inverted OPVs are exhibiting significantly longer lifetime performance compared to normal structure OPVs, another important parameter for OPV commercialization [3]. The presentation will cover recent advances in developing high-performance metal oxides carrier selective contacts and Indium-tin-oxide (ITO)-free electrodes for non-fullerene acceptors (NFA) based Inverted OPVs. High-performance NFA inverted OPVs incorporating solution processed metal oxide hole selective contact (HSC) providing similar PCE and light stability  performance to that achieved with the commonly used thermally evaporated MoO₃ HSC will be presented [4]. Furthermore, the presentation will highlight the systematic understanding of the relationship between doped metal-oxide and Ag nanowires (NWs) interfaces that allowed the development of Ag-NWs based bottom transparent electrodes for inverted configuration OPVs with simplified processing [5]. Finally, laser printed nanoparticle-based metal grids for the development of  efficient ITO-free Inverted OPVs with up-scalability perspectives will also be presented [6].

ZnO has been widely used as an electron transport layer (ETL) in organic photovoltaics (OPVs) to facilitate photo-generated electrons extraction due to its appropriate band alignment with various active absorbing layers. Typically, ZnO ETLs are prepared by solution-based techniques such as spin coating. However, with spin coating, it is difficult to control the oxygen stoichiometry, which has great impacts on the defects formation and hence materials properties of ZnO. For example, carrier mobility and optical transparency would affect charge transport and light utilization of the active layer. Moreover, surface defects at the interface between ZnO and the active layer could have great impacts on the stability of the devices.

In this work, we deposited ZnO thin films by radio frequency magnetron sputtering and studied the effects of deposition conditions on the materials properties of the ZnO. Furthermore, the sputtered ZnO were integrated in OPVs with a non-fullerene acceptor-based absorber, PM6:Y7. Our results show that sputtered ZnO on indium tin oxide (ITO) coated glass are polycrystalline and have high optical transparency of >85% in the visible region, which is comparable to a bare ITO glass substrate. Substrate temperature, oxygen flow rate ratio of the sputtering gas ([O₂]/[Ar+O₂]) and thickness of the ZnO all have significant effects on the OPV device performance. The roles of oxygen stoichiometry on OPV device performance were investigated by photoemission spectroscopy and J-V measurements. Our results indicate that a higher [O₂]/[Ar+O₂] effectively reduces the concentration of oxygen-related defects, resulting in improved device performance. Utilizing a two-step sputtering process to suppress interfacial defects, solar cells using optimized sputtered ZnO deliver a higher power conversion efficiency than using spin-coated ZnO. Lifetime measurements under controlled environments were carried out to evaluate the stability of the devices. The difference in stability is explained by the ZnO/PM6:Y7 interfacial quality, and can be related to the difference in defect concentration at the ZnO surface.

In summary, we have investigated the effects of different sputtering conditions of ZnO ETLs on PM6:Y7 device performance. Devices using optimized sputtered ZnO ETLs outperform those using spin-coated ZnO ETLs. Moreover, our results suggest that the tuning of ZnO surface defects through the manipulation of oxygen stoichiometry plays a crucial role on the interfacial quality between ZnO ETL and the active layer, which in turn can be used to optimize the interface stability and device lifetime. Our findings highlight the potential of sputtered ZnO as a promising ETL in highly efficient non-fullerene acceptor based organic photovoltaics.

This research involved the creation via the coaxial electrospinning process of flexible core/shell nanofibrous mats with high porosity that can serve as alternative porous structures to the brittle porous TiO₂-based photoelectrodes currently in use. The core was made from polyethylene terephthalate (PET), while the shell consisted of a PET-Titanium dioxide (PET-TiO₂) nanocomposite. Two different shapes of TiO₂ (nanobars and nanorhombics) were synthesized via the solvothermal method and then incorporated at various concentrations (0-20 wt.%) into the shell layer of the nanofibers to enhance their optical, thermal, and mechanical properties. The study investigated the surface morphology, porosity, specific surface area, thermal stability, dye adsorption, optical, and mechanical properties of the developed nanofibrous mats. Particular emphasis was placed on understanding the impact of solvent miscibility and solvent composition on the morphology of the fibrous mats. Various characterization techniques confirmed the successful incorporation of TiO₂ nanoparticles into the shell layer of the nanofibers. It was observed that adding up to 15 wt.% TiO₂ within the shell layer enhanced light harvesting and shifted the UV-Visible absorption edge of the nanofibrous mats to larger wavelengths. Moreover, PET/(PET-TiO₂) core/shell nanofibrous mats obtained with nanobars TiO₂ showed higher thermal stability due to a better TiO₂/PET interfacial interaction. Photoluminescence results confirmed the efficient charge transfer between TiO₂ nanoparticles and PET with a minimum recombination of the photogenerated charges. Furthermore, the high porosity of the coaxial electrospun mats, ranging from 75% to 81%, had a positive impact on the diffusion of dye molecules and their subsequent adsorption on the surface of the mats.

Finally, we believe that this detailed study on PET-TiO₂ core-shell nanofibrous structures provides new insight for further development of optimum DSSC photoanode microstructure at low temperature and contribute towards achieving efficient flexible DSSCs.

The performance optimization of organic solar cells is influenced not only by the design of the molecular structures but also by the regulation of the blend morphologies. Currently, there is a well-established understanding of how material design can regulate energy levels, film absorption, carrier mobility, and molecular crystallinity, leading to efficient device performance through the aggregation regulation of active layers. However, there is a lack of effective methods and investigations on the regulation of the metastable state of the active layer, the analysis of degradation mechanisms, and the improvement of operational stability. At present, organic solar cells are not only facing the basic problem of unclear metastable decay mechanism, but also facing the important challenge of synergistic development of "efficiency and stability". The development of physical and chemical methods of metastable regulation is an important breakthrough point for future work. On the basis of levelized cost of electricity analysis, this report will briefly indicate the performance requirements of organic photovoltaic materials and a brief analysis of performance improvement strategies and introduce the metastable morphology characteristics of active layer. By analyzing and revealing the attenuation mechanism of metastable morphology, combined with the intrinsic characteristics of small molecule materials, this report is used to understand the morphologic changes of the active layer under light/thermal stress, and explore the physical attenuation dynamics. Finally, the recent progress made by our research group in regulating the metastable state through physical and chemical methods, as well as the coupling strategies employed. This report aims to provide theoretical support for a deeper understanding of the mechanisms behind metastable morphology attenuation, and to offer valuable references for fellow researchers in the field.

Abstract

Recently, non-fullerene acceptor based organic solar cells show a significant improvement in power conversion efficiency. However, rapid degradation occurs under illumination, particularly when photocatalytic metal oxide electron transport layers are used in these devices.[1,2] We introduced vitamin C (ascorbic acid) into the organic solar cells as a photostabilizer and systematically studied its photostabilizing effect on inverted PBDB-T:IT-4F devices. The presence of vitamin C as an antioxidant layer between the ZnO electron transport layer and the photoactive layer strongly suppressed the photocatalytic effect of ZnO that induces NFA photodegradation. Upon 96 h of exposure to AM 1.5G 1 Sun irradiation, the reference devices lost 64% of their initial efficiency, while those containing vitamin C lost only 38%. The UV–visible absorption, impedance spectroscopy, and light-dependent voltage and current measurements reveal that vitamin C reduces the photobleaching of NFA molecules and suppresses the charge recombination. This simple approach using a low-cost, naturally occurring antioxidant, provides an efficient strategy for improving photostability of organic semiconductor-based devices.

The synthesis of carbon nano-rings and related structures opens a new field in the chemistry of cyclic conjugated systems with structural, dynamic and optical properties different from their counterparts, the linear conjugated systems.They possess unique zise-dependent optoelectronic properties that make them ideal candidates for use in nanoelectronics and photovoltaics. For this reason, the simulation of photoinduced processes is a substantial and complementary contribution to a better understanding and control of these systems.

I will present the results of our study of the structure-dynamics-optical properties relationship in carbon nano-rings and other cyclic conjugation systems. We performed the simulation of photoinduced dynamics in them. It was possible to find quantum confinements, electronic delocalization, thermal fluctuations, structural deformations and vibrational couplings during the non-radiative relaxation process, which are responsible for the changes observed in the optical properties.

The correct description of these processes requires atomistic simulations of non-adiabatic molecular dynamics (i.e., more than the Born-Oppenheimer approximation) considering multiple coupled excited electronic states. Using the NEXMD package it is possible to perform the calculation of the electronic structure, “on the fly”, i.e., the energies, energy gradients and non-adiabatic
couplings of the different excited electronic states are calculated at each step of the dynamics. In addition, nuclear propagation is performed using the hybrid classical-quantum hybrid method of quantum jumps. This method identifies the electric couplings during nuclear propagation.

tbc

The efficiency of poly(3-hexylthiophene) (P3HT) – nonfullerene acceptor (NFA) based bulk heterojunction (BHJ) solar cells lacks considerably behind many other polymer donor:NFA systems. For reasons which are yet incomprehensible. Here, we report on a series of P3HT:NFA solar cells, and  elucidate the origin of performance losses in terms of the photophysical processes. It is a matter of fact that the interfacial ionization energy (IE) offset is a critical parameter in NFA-based blends in determining the efficiency of the exciton-to-charge transfer (CT) state conversion. We show that while large IE offsets in excess of >0.9 eV still facilitate complete exciton quenching, the device internal quantum efficiency (IQE) is limited by geminate and / or non-geminate recombination processes in P3HT-based photoactive blends. Our finding shows a drop in IQE when the diagonal bandgap of the photoactive blend i.e the difference between the IE of the donor and the electron affinity (EA) of the acceptor is small irrespective of the IE offset. Understanding the relationship between the IE offsets, EA offsets at the interface of donor and acceptor materials, and the performance of organic solar cells (OSC) could improve the charge generation efficiency. Thus, enables us to understand the relation between small diagonal bandgap and the decrease of the IQE in energy gap law framework.

Compared to single junction solar cells, multi-junction architectures can harvest a wider range of the sun´s spectrum while reducing thermalization losses, thus potentially leading to larger efficiencies [1, 2]. Regardless of the specific geometry, i.e. stack, spectral splitting or rainbow, material systems with band gaps wider and narrower than the single junction optimum should be developed to fully exploit the multi-junction concepts [2]. Importantly, the specific materials combination, as well as device parameters (e.g. thickness) are strongly correlated in a multiparametric optimization problem.

In this contribution, we will show our current strategy to tackle this challenge: combining high throughput material screening methods [3] with a spectrum on demand light source [4]. In particular, we focus on materials with narrow bandgap, for which we have screened more than 15 systems, and wide bandgap for which we investigated 9 material combinations and two solvents. Then, we use the best systems to build Rainbow solar cells, i.e. an in-plane spectral splitting geometry in which a series of sub-cells are placed next to each other laterally, and illuminated through an optical component that splits the incoming white beam into its spectral components, thus matching local spectrum and absorption for each sub-cell [5].

[1]        D. CarloRasi and R. A. J. Janssen, “Advances in Solution-Processed Multijunction Organic Solar Cells,” Advanced Materials, 31 (2019) 1806499.

[2]       I. M. Peters et al, “Practical limits of multijunction solar cells”, Prog. In Photovolt. 31 (2023) 1006.

[3]       A. Harillo-Baños et al, “Efficient Exploration of the Composition Space in Ternary Organic Solar Cells by Combining High-Throughput Material Libraries and Hyperspectral Imaging”, Adv. Ener. Mater., 10 (2020) 1902417.

[4]        M. Casademont-Viñas et al “Spectrum on demand light source (SOLS) for advanced photovoltaic characterization”, Rev. Sci. Instrum. 94 (2023) 103907.

[5]       M. Gibert-Roca et al, “RAINBOW Organic Solar Cells: Implementing Spectral Splitting in Lateral Multi-Junction Architectures” Adv. Mater (2023) 2212226.

Technological deployment of organic photovoltaics (OPV) requires improvements in device light-conversion efficiency and stability while keeping material costs feasible. Non-fullerene small molecule acceptors emerged as a new horizon pushing the boundaries of OPV and bring them back to competition with other solution processed photovoltaics with unique properties such as semitransparency and power per weight. The power conversion efficiency of OPV has reached 19% in just a couple of years after replacing fullerene alternatives. Non fullerene acceptors are inherently more stable than fullerene derivatives. However, they do still suffer from long term photo and thermal stabilities. There is an understanding gap where we look into acceptors and donot structure-proprty relationships to understand the performance-stability relationship.

In this talk, I will talk how NFAs exceeded the limits of fullerenes and share approaches to overcome photo and thermal stability issues. Finally, I will share state-of-the-art activities on transparent OPV and their scale-up and deployment in potential areas such as greenhouses.

Recent advancements in Organic Solar Cells (OSCs) have led to peak efficiencies of up to 19%, primarily due to the development of novel organic molecules for active and transport layers. Despite this progress, OSC technology still encounters commercialization challenges. These are largely attributed to the extensive range of potential materials and the intricate interplay between their structures and properties, which complicates efficiency predictions. Addressing this, the materials science field is increasingly utilizing machine learning (ML) to decipher structure-property correlations.

Our research addresses this challenge by exploring the relationship between the electrical properties of OSCs, such as Power Conversion Efficiency (PCE) and Fill Factor (FF), and their structural features, including band center position and crystallinity. These are determined through the deconvolution of UV-Visible (UV-VIS) spectroscopy data. By employing Gaussian Process Regression, we have devised a method that predicts solar cell efficiency using only UV-VIS spectra. This approach potentially eliminates the need for evaporation and IV measurements, streamlining the process and reducing costs.

To ensure predictive accuracy, we compiled a dataset of 25 donor-acceptor combinations, yielding a total of 200 cells with intentional variations in film thickness and crystallinity. We ensured exceptional homogeneity in layer preparation using the Autonomous Materials and Device Application Platform (Amanda) ¹. Analysis of this dataset enables us to foresee the performance of new material combinations. This significant breakthrough in OSC research could expedite the development of efficient and commercially viable solar cell materials.

Implementation of 2D materials in organic photovoltaics (OPV) is one of the promising routes to modify fundamental device properties, and potentially improve device efficiency and stability due to their unique properties such as tunable electronic structure, high charge carrier mobility and high optical transparency. For MXenes, a family of 2D transition metal carbides and nitrides, the ability to tune work function via surfaces termination routes have made it especially promising as contact layer material in solar cell devices. In this work, we employ such 2D MXene, Ti₃C₂T_x, in electron transport layers (ETL) to develop composite 2D based ETL, and demonstrated their high performance for non-fullerene acceptor (NFA) based OPV. The composite 2D-ETL based OPV resulted in robust ETL-organic interfaces with efficient electron extraction and transport properties for high device performance (~14% using green solvents), and importantly, significantly prolonged device lifetime when compared to conventional 2D-free ETL based OPV. The integration of the 2D MXene interlayers in OPV is explored in terms of morphological, optical, and electrical properties along with ISOS-L device lifetime measurements. Importantly, photoelectron spectroscopy results provide insights into the modified surface defect state concentration on the ETL surface, which can directly be related to the improved device stability. The work demonstrates the unique potential of MXene as contact layer material in high performance organic photovoltaics with prolonged device lifetimes.

While multi-junction geometries have the potential to boost the efficiency of organic solar cells, the experimental gains yet obtained are still very modest.[1,2] This work proposes an alternative spectral splitting device concept in which various individual semiconducting junctions with cascading bandgaps are laid side by side, thus the name RAINBOW. Each lateral sub-cell receives a fraction of the spectrum that closely matches the main absorption band of the given semiconductor. Here, simulations are used to identify the important material and device properties of each RAINBOW sub-cell. Using the resulting design rules, three systems are selected, with narrow, medium, and wide effective bandgaps, and their potential as sub-cells in this geometry is experimentally investigated. With the aid of a custom-built setup that generates spectrally spread sunlight on demand, the simulations are experimentally validated, showing that this geometry can lead to a reduction in thermalization losses and an improvement in light harvesting, which results in a relative improvement in efficiency of 46.6% with respect to the best sub-cell. Finally, a working proof-of-concept monolithic device consisting of two sub-cells deposited from solution on the same substrate is fabricated, thus demonstrating the feasibility and the potential of the RAINBOW solar cell concept.

Organic Photovoltaics have seen a significant increase in power conversion efficiency (PCE) recently, approaching 20% on small lab cells. However, the record efficiencies on module level are still substantially lower (~30%, relatively). Hence, it is necessary to perform focused upscaling research to reduce the gap between small-area cells and large-area modules. In this work, we present successful upscaling of devices based on PM6:Y6-C12:PC₆₁BM, processed in air from non-halogenated solvents, from cells (0.1 cm²) to large-area modules (>200 cm²) with barely any performance losses. High PCEs of >14% on total module area (>15% with respect to active area) are achieved by utilizing accelerated blade coating to eliminate thickness gradients in the layers. Inactive (interconnect) areas are significantly reduced by high-resolution short-pulse (nano- and femtosecond) laser patterning to achieve high geometric fill factors exceeding 97%. The results are confirmed by independent certified measurements.Organic Photovoltaics have seen a significant increase in power conversion efficiency (PCE) recently, approaching 20% on small lab cells. However, the record efficiencies on module level are still substantially lower (~30%, relatively). Hence, it is necessary to perform focused upscaling research to reduce the gap between small-area cells and large-area modules. In this work, we present successful upscaling of devices based on PM6:Y6-C12:PC₆₁BM, processed in air from non-halogenated solvents, from cells (0.1 cm²) to large-area modules (>200 cm²) with barely any performance losses. High PCEs of >14% on total module area (>15% with respect to active area) are achieved by utilizing accelerated blade coating to eliminate thickness gradients in the layers. Inactive (interconnect) areas are significantly reduced by high-resolution short-pulse (nano- and femtosecond) laser patterning to achieve high geometric fill factors exceeding 97%. The results are confirmed by independent certified measurements.

The pursuit of more efficient buildings is driving digitalization, leading to a rapidly growing need for connected sensors. These sensors typically rely on batteries, necessitating costly maintenance to replace them every few years and contributing to a significant environmental impact.

By harnessing ambient energy, the lifespan of batteries can be extended, and in many cases, batteries may become unnecessary. Circumventing the issues with batteries will enable much easier deployment of distributed sensing, facilitating data collection that, in turn, yields a more energy-efficient society. Light is a primary source of ambient energy in buildings, and organic solar cells can be tuned to harvest that light energy with high efficiency. Examples of applications for connected devices suitable for light energy harvesting include electronic shelf labels, asset tracking labels, and consumer electronics such as remote controls.

Epishine, an innovative Swedish company, has developed a scalable manufacturing process for organic solar cells using roll-to-roll printing and lamination technologies. This technology puts Epishine in a favorable position to address the increasing demand for high-performance indoor solar cells. In this presentation, I will provide an overview of Epishine's technology and manufacturing process, as well as present some of Epishine’s internal research efforts based on our unique approach to producing OPV [1]