Organic solar cells based on non-fullerene acceptors have achieved remarkable power conversion efficiencies exceeding 21%. While polymer donor/small-molecule acceptor systems exhibit excellent light-harvesting capability and charge transport, their limited optical, thermal, and mechanical stability restricts long-term applications. In contrast, all-polymer solar cells (all-PSCs), composed of polymer donors and polymer acceptors, offer enhanced structural tunability and superior mechanical and thermal robustness, making them attractive for wearable electronics, flexible devices, and building-integrated photovoltaics. However, the development of high-performance all-PSCs remains challenging due to the scarcity of narrow-bandgap, strongly absorbing polymer acceptors. Advancing all-PSC performance requires the design of novel polymer acceptors and precise control over active-layer morphology as well as batch-to-batch insensitive materials. Furthermore, real-time monitoring of polymerization and batch-consistent polymer synthesis represent critical scientific challenges for large-scale implementation. This presentation highlights recent progress and future opportunities for efficient and stable all-PSCs.

Spin interactions have emerged as fundamental in organic photovoltaics.[1,2] In this framework, chiral molecules offer an exciting route to control the spin degree of freedom via the chirality-induced spin selectivity (CISS) effect.[3] Recent breakthroughs have enabled the direct detection of CISS in electron donor-acceptor dyads.[4] These studies show that CISS governs the spin dynamics of photoinduced charge transfer through chiral bridges at the molecular level. Understanding the molecular origin of CISS and identifying its key molecular parameters are now pressing priorities.[5,6]

Here, we present new systems consisting of a thiabridged[4]helicene donor covalently linked to a perylenediimide (PDI) acceptor through bridges of variable length. Transient absorption and time-resolved electron paramagnetic resonance (TREPR) spectroscopies reveal that the spin selectivity of charge transfer and triplet formation pathways strongly depends on the bridge design. Orientation-dependent TREPR experiments of the longer chiral dyad and its achiral analogue disclose the generation of distinct spin-polarized radical pair signals. Complementary theoretical simulations clarify the molecular origin of the CISS effect and show that the electron motion through the chiral bridge is essential for its observation.

These results add another piece to the puzzle of chirality in donor-acceptor dyads, with the final aim of exploiting CISS to control electron spin states for applications in photovoltaics and quantum information science.

Emerging semiconductors, particularly organic conjugated molecules and metal halide perovskites, are transforming the semiconductor industry and serving as foundational materials for next-generation technologies, including solar panels, displays, lighting, and sensing devices. In photovoltaics, perovskite solar cells have already achieved an impressive power conversion efficiency of 27%, while organic solar cells have surpassed 20%. However, despite their remarkable device performance, several challenges still hinder large-scale commercialisation.

A key factor in realising the full commercial potential of organic solar cells is stability; a photovoltaic device must possess a sufficiently long lifespan to exceed the operational requirements of its intended application. The limited stability of conventional fullerene-based organic solar cells has long been recognised as a major challenge, with multiple degradation mechanisms leading to rapid performance losses under illumination, ambient exposure, and thermal stress. Nevertheless, the transition from fullerene to non-fullerene acceptors, alongside significant advances in molecular and device design, has opened exciting opportunities to fully address this issue.

For perovskite solar cells, one of the most critical concerns is their potentially high ecotoxicity, primarily due to the use and subsequent leaching of excessive amounts of lead into the environment over the product’s lifetime. How to minimise the risks of lead release fromthese materials into the environment without compromising device performance remains a majorchallenge.

In this talk, I will summarize my group's recent research progress in addressing the stability and environmental challenges of organic and perovskite materials and solar cells. For organic solar cells, I will highlight the distinct roles of donor and acceptor materials in degradation and propose potential strategies to mitigate these degradation mechanisms. For perovskite solar cells, I will examine the lead leaching mechanisms of halide perovskite materials under various environmental conditions and demonstrate how rational materials and device design can help overcome this challenge.

Organic photovoltaics are in a new era of high efficiency materials and exceptional intrinsic device stabilities. Major hurdles along the frontier towards widespread deployment of OPV are related to the necessary tasks of transitioning out-of-lab and into-real-world R&D. Scaling up module processing while retaining performance, outdoor and accelerated durability testing, and material and manufacturing costs are the primary areas of focus for commercialization. In the talk, I will present our team's progress on each of these areas. While targeting multi-use applications uniquely captured by OPV due to infinitely tunable semitransparent device designs, we show that the process of going from inception of new organic semiconductors all the way to validated technology can be accelerated through intentionally low-cost and rapid protocols at each stage of molecular design, material performance screening, small area device optimization, upscaling to modules, as well as accelerated stress testing. Finally, high durability is crucial to widespread industry uptake, and outdoor durability performance testing is a must for proving out OPV as a real-world technology and validating/informing accelerated stress test projection models with empirical results. We show exceptional module lifetimes outdoors in multiple climate zones in the United States. Using biomatched OPVs as a target multi-use application for next-generation agrivoltaics, energy production models will be presented to show how even modest efficiencies in biomatched OPVs provide substantial practical and economic incentives.

Integrating biomatched organic photovoltaic (OPV) modules into greenhouses and polytunnel cladding enables a next-generation of agrivoltaics where crop and solar energy production land-use tradeoffs are eliminated. Spectral tuning via molecular design is key to transmitting plant light requirement wavelengths while harvesting other wavelengths for electricity. In this presentation we demonstrate the development of numerous biomatched photoactive layers using BT-CIC (4,4,10,10-tetrakis(4-hexylphenyl)-5,11-(2-ethylhexyloxy)-4,10-dihydrodithienyl[1,2-b:4,5b′ ]benzodithiophene-2,8-diyl)bis(2-(3-oxo-2,3-dihydroinden-5,6-dichloro-1-ylidene)malononitrile)), a near infrared absorbing high performance non-fullerene acceptor. Polymer donors are algorithmically screened from our organic semiconductor database for a target spectral compatibility with BT-CIC to produce biomatched active layers for a given plant species. With only the need to produce the standalone OPV thin film, photoconductance and charge-carrier lifetimes via Time Resolved Microwave Conductivity (TRMC) measurements further down-select high performance potential OPV biomatches. Using the example of BT-CIC, we show how biomatching and TRMC rapidly assess material performance to inform highest prioritization of device optimization of brand new active layer combinations. Finally, a higher-level scenario analysis is presented that combines synthetic complexity and material cost, ultimately towards the goal of accelerating commercialization and deployment of OPV. 

In this work, we measured the photovoltaic responses of two structurally similar small-molecule donors synthesized at Heliatek GmbH—DCV-Me and DCV-iPr—which exhibit strikingly different performances despite differing by only one isopropyl substituent. To uncover the origin of this contrast, we performed a comprehensive experimental–theoretical study, combining crystal structure prediction, vapor deposition simulations, single-crystal X-ray diffraction, GIWAXS analysis, photovoltaic characterization, voltage loss studies, as well as state-of-the-art exciton-vibronic calculations to simulate the optical steady-state spectra and relate the differences to the distinct packing motifs of the two systems.

We find that steric effects from the isopropyl group in DCV-iPr result in a brick-wall molecular arrangement, resolved in the crystal structure and preserved in evaporated thin films. Our excitonic calculations reveal that this geometry promotes J-like excitonic interactions, sharp absorption features, and a reduced Stokes shift—favorable for efficient solar energy conversion. In contrast, as predicted by our theoretical model and confirmed experimentally, DCV-Me forms H-like aggregates with broadened absorption, increased voltage losses and poor photoconversion efficiency. 

We next investigate the aggregation behavior of dipyrrolonaphthyridinedione (DPND) chromophores in the solid state critically determines their optoelectronic properties. Here, we investigate how systematic variation in the side-chain geometry—specifically the branching point and steric profile—governs molecular packing and excitonic coupling. Using crystal structure prediction (CSP) combined with experimental GIWAXS and solid-state NMR, we obtain the packing geometry and crystal structure for three DPND derivatives (DPND-iPr, DPND-EtPr₂, and DPND-iBu). The results reveal that side-chain branching at the first carbon atom promotes herringbone packing and J-type behavior, while branching at the second carbon induces brick-wall stacking and H-type behavior in the solid state. Optical simulations based on the Holstein exciton-vibrational Hamiltonian reproduce experimental absorption and photoluminescence spectra, confirming the transition from J-like to H-like photophysics as the side-chain branching position shifts. This study demonstrates that fine-tuning alkyl side-chain geometry enables rational control of aggregation and excitonic behavior in cross-conjugated DPNDs, providing new design principles for functional organic semiconductors.

The performance of organic electronic devices, such as solar cells, depends on understanding and controlling the solid-state microstructure of semiconducting polymers. In this presentation, I will discuss our recent understanding of the aggregate states, solid-state microstructure, and thermotropic behavior of the best-performing family of polymers for solar cells, i.e., benzodithiophene-based semiconducting polymers. The following argument will be put forward: that the microstructure of high-performing donor semiconducting polymers does not conform to the traditional structural models developed for polymers, i.e., the amorphous and semi-crystalline models, nor with established polymeric solid mesophases (e.g. vitrified liquid crystals, condis crystals, columnar mesophases, etc.). Instead, these polymers organize into a singular solid mesophase that bears a resemblance to sanidic structures, while concurrently exhibiting characteristics reminiscent of columnar mesophases. Furthermore, recent results on the quantitative analysis of the structural aspects in these materials, using GIWAXS and Ultra-fast chip calorimetry, will be presented. Finally, the discussion will extend to the question of whether these materials exhibit an amorphous phase, as is the case with "regular" polymers.

The sun’s photons represent the largest energy resource on Earth, and harnessing this energy could help address the global energy crisis without harming the environment. Organic semiconductors, whether polymers (typically electron donors) or small molecules (such as fullerene and non-fullerene acceptors), can be dispersed in water under the form of nanoparticles, to produce environmentally and human-friendly inks for processing photovoltaic active layers, offering an alternative to conventional approaches that rely on toxic organic solvents.

Consequently, there is a strong need to investigate:

• the synthesis of organic semiconducting aqueous dispersions
• the integration of these inks into solar-cell fabrication processes
• the photovoltaic performance of the resulting device

In this communication, I will present the current state of this technology as well as the advances we have achieved over the past five years. In particular, I will discuss how the synthetic methodology used to prepare the dispersions influences their properties, the impact of surfactants on the internal donor-acceptor morphology of the particles and on ink deposition, and finally, the crucial role of thermal annealing in achieving optimal photovoltaic efficiencies, which now exceed 10%.

The change in energy paradigm towards sustainable sources implies the large scale deployment of highly efficient solar technologies. Novel technologies are needed for integration into buildings (lightweight, high incidence angle tolerance and neutral color), windows (semitransparency), greenhouses (complementary transmission with plant needs), infrastructure (robustness, integrability), wearables (lightweight, flexibility), indoor photovoltaics (high tolerance to low irradiances) as well as beyond photovoltaic farms (ever increasing efficiency). Organic based photovoltaics are well suited for this huge challenge, as can be produced with the largest color pallet and transparency degree imaginable, as well as tunable flexibility, lightweight, etc. Indeed, there is an infinite number of molecules that can be synthesized to match our needs. The bottleneck, then, becomes how to identify and screen the best potential candidates and device structures for each application.

In this talk, we will show our current strategy to tackle this challenge: combining high throughput material screening methods [1, 2] with a spectrum on demand light source [3]. First, we will briefly describe a novel methodology for the fast evaluation of organic semiconductor systems for photovoltaics based on samples with gradients in the relevant parameters of interest (thickness, microstructure, composition) coupled to hyperspectral imaging. Then, we will present a combinatorial screening consisting of thousands of solar cells, centered on wide bandgap materials for indoor applications, narrow bandgap for agrivoltaic applications and panchromatic absorption for urban photovoltaics.

The remarkable recent advances in photovoltaic energy conversion efficiency in molecular materials have resulted largely from the use of fused ring molecular acceptors that form strongly coupled domains in the solid state. These materials appear able to support efficient photocurrent generation with relatively small energetic offset between the ionization potential of donor and acceptor components, and the best performing molecular materials may even support charge pair generation in single material domains. In this work we investigate the behaviour of these materials by combining experimental measurements of charge generation in single-component and heterojunction devices with a computational model of the generation and evolution of delocalised excited states in such systems. We consider the influence of factors such as the nature of the charge separating heterojunction, molecular packing, energy and charge transport, electron-phonon coupling and loss pathways. We explore the impact of molecular parameters and find that low exciton reorganization energy and high and isotropic electronic coupling are important for efficient photogeneration. We go on to apply the same framework to polymer materials and tethered donor-acceptor structures. Finally, we will address the limits to energy conversion efficiency in such systems.

Continuous flow chemistry offers a fast entry to commercial production for innovative polymers of diverse nature. A field that could hugely benefit from this gateway is organic electronics. For some of the most promising organic semiconductor technologies, notably organic photovoltaics, push-pull type conjugated polymers have afforded the optimum performance metrics to date. However, the production of these polymers by classical batch synthesis procedures is accompanied by inherent issues regarding the reproducibility of material properties, such as molar mass, end-group fidelity, and structural defects, which significantly impact the final device performance. Flow chemistry could provide (part of) a solution here, but its full potential still has to be unravelled and embraced by the academic community as well as the interested industries.

In this presentation, I will illustrate how batch-to-batch reproducibility in the synthesis of push-pull type conjugated polymers has been hindering progress in the field over the last 15 years, and how continuous flow chemistry can be applied to address this issue.[1,2] On top, some examples will be given to show how flow methods can be beneficial for molar mass or homocoupling defect screening, and for the construction of all-conjugated block copolymers for single-component organic solar cells.[3]

Although organic solar cells (OSCs) have surpassed 20% power conversion efficiency, a persistent trade-off between open-circuit voltage (V_OC) and fill factor (FF) prevents them from closing the gap with inorganic technologies. Here, we systematically investigate this trade-off across a wide range of devices and identify an FF limit arising from field-dependent free charge generation. This limit becomes more severe as voltage losses get minimised, thus imposing a V_OC-FF compromise. To quantitatively describe this limit, we combine drift-diffusion simulations with an analytical model for field-dependent charge generation, revealing that the underlying cause is the field-sensitive charge transfer process between excitons and charge-transfer states. Guided by this physics-based model, we highlight that increasing the exciton lifetime is a practical and effective strategy to mitigate the FF limit. By applying our approach, we demonstrate a ternary OSC combining a high FF of 81% with a power conversion efficiency of over 20%, showcasing a clear path to overcoming this fundamental challenge.

Self-assembled monolayers (SAMs) have previously been shown to perform well as hole-selective layers in solution-processed organic solar cells (OSCs) [1-5]. In this work, we investigated the feasibility of several common spin-coated carbazole SAMs – 2PACz, MeO-2PACz, and Br-2PACz, spanning a range of HOMO levels and work functions from about -4.5 to -6 eV – for integration in vacuum processed fullerene-based OSCs with DTDCPB or DCV4T as donor molecules, with HOMO energies of approximately –5.4 and –5.8 eV respectively. We found that certain SAMs increased the power conversion efficiency of the DTDCPB and DCV4T OSCs by up to 20% and 13% respectively relative to that of our control devices with a standard MoO_x hole contact: this relative enhancement in performance was linked to improvements in open circuit voltage (V_OC) which occurred if the HOMO of the SAM was below that of the donor. We used capacitance voltage measurements to directly determine the built-in voltage (V_bi) of each OSC and demonstrated that the trend in V_bi closely follows the V_OC and the energetic alignment of the different SAMs relative to each donor.  These results can be used to help guide future SAM-donor combinations in OSCs. As vacuum thermal evaporation is a readily-scalable fabrication method [6], we seek to make fully evaporated SAM-based OSCs. In preparation for this, we attempted to evaporate the aforementioned SAMs. We have so far found that Br-2PACz degraded during attempted evaporation, but we were able to successfully evaporate 2PACz, in agreement with literature [7]. In this presentation, we aim to compare the fully evaporated device stacks to their solution processed counterparts. We will also complete complementary characterisation to confirm the same energetic changes occur, and we plan to attempt stability testing on these devices. 

Solution-processed bulk heterojunction (BHJ) organic solar cells (OSCs) have emerged as a promising next-generation photovoltaic technology. A rapidly growing strategy in this field is the use of solid additives (SAs) to precisely tailor BHJ morphology and unlock the full potential of OSCs. SA engineering provides several advantages for commercialization, including: i) tuning film-forming kinetics to accelerate high-throughput manufacturing; ii) exploiting weak noncovalent interactions between SAs and active-layer materials to enhance device efficiency and stability; and iii) simplifying processing steps to enable cost-effective, scalable fabrication. These benefits position SA engineering as a key driver for advancing OSC technologies. However, the fundamental principles governing the discovery of high-performance SAs remain unclear. In this presentation, I will introduce a closed-loop workflow that integrates high-throughput experimentation—with the capacity to generate large and diverse datasets—with Bayesian optimization to discover promising SAs for high-efficiency OSCs. By building predictive models based on molecular descriptors, we established clear correlations between SA molecular structure and device performance. Through this data-driven approach, we successfully identified a series of high-performance SAs from minimal iterative suggestions, enabling the realization of highly efficient OSCs.

    In this report, we will discuss the results of our systematic study of a broad panel (>250 structures) of conjugated polymers [1] and small molecules, including fullerene derivatives [2] and non-fullerene acceptors (NFAs), in the context of their stability with respect to light and gamma rays. Important correlations between the materials’ stability, their chemical compositions and molecular structures will be presented. The first prognostic model enabling an accurate prediction of photostability of arbitrary chosen conjugated polymer structures will be introduced, and the guidelines for rational design of new absorber materials for stable and efficient organic photovoltaics will be outlined.

Emerging photovoltaics, such as organic or perovskite based photovoltaics, can contribute to a more sustainable society. However, marketability of emerging PV still requires improvements of materials and processes towards higher efficiency, better stability, and lower cost. Using domain knowledge driven “trial and error” experimentation, improvements occur only slowly. Artificial Intelligence driven (AI) workflows can replace the trial and error search by systematic sampling of chemical and processing space, which is expected to dramatically increase the speed of discovery of record breaking materials or smart processes. However, AI driven workflows typical require large training datasets, a no-go for experimental science.

In this presentation, I show how the incorporation of physics knowledge allows building of workflows that can learn from less than a hundred different individual experiments. These workflows can be deployed in single labs or small consortia and should thus allow a general acceleration of innovation in our field. Essentially, we use quantum chemical simulations to incorporate quantities into the training dataset that serve as proxies for the properties of interest.

We have used this workflow successfully to discover new organic hole transport molecules for perovskite solar cells[1], to find organic semiconductors with strongly selective light absorption [2], and to identify radiation hard organic semiconductors for space applications and radiation detectors. Finally, I will discuss multi-objective optimizations which are essential for marketability, where several requirements must be matched at the same time.

The increasing number of indoor appliances used daily has greatly accelerated the advancement of Internet of Things (IoT) technologies. As a result, the rapid expansion of IoT presents a significant challenge for powering these devices. Currently, most are battery-powered, which imposes limitations such as frequent replacements, maintenance issues, and environmental concerns due to toxicity..

In this context, organic photovoltaics (OPVs) offer a promising alternative because of their energy-efficient production, lower environmental impact, and design flexibility. Notably, OPV devices have demonstrated high efficiency and excellent stability under indoor lighting conditions.

Consequently, indoor organic photovoltaics have emerged as a key candidate for powering low-consumption IoT devices across various fields such as electronics and sensing. It is therefore important to develop custom-designed photovoltaic devices to facilitate seamless integration into final products.

Inkjet printing has attracted considerable attention as a technology for large-scale fabrication of flexible and stretchable electronics due to its many advantages. It provides freedom in form and design on various substrates with good reliability, high time efficiency, low manufacturing cost, and reduced material usage compared to other deposition techniques.

These unique features have made inkjet printing an enabling technology for cost-effective production, drawing researchers’ interest in functional devices such as photovoltaic solar cells.

Nonetheless, several challenges remain, including ensuring ink stability to prevent nozzle clogging, controlling wetting properties, and matching ink viscosity and surface tension with printhead requirements.

In this work, we present fully inkjet-printed organic photovoltaic cells and modules with high efficiency, tailored for indoor applications, offering versatile shapes and designs, developed by Dracula Technologies.