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.

Light-emitting electrochemical cells (LECs) can be fabricated by scalable printing under ambient conditions using widely available raw materials, making it a material- and resource-efficient light-emitting technology. The LEC can feature a robust three‑layer architecture in which the active layer (AL), commonly a blend of an electroluminescent organic semiconductor (OSC) and a salt dissolved in an ion transporter, is sandwiched between two electrodes. Under applied bias, the mobile ions in the AL redistribute to form p‑ and n‑doped regions, whose junction delivers the light emission.¹

This study investigates the influence of the molecular weight of a hydroxyl‑capped trimethylolpropane ethoxylate (TMPE‑OH) ion transporter on the time to reach minimum voltage for an LEC, comprising KCF₃SO₃ as the salt and Super Yellow as the OSC. We find that the employment of the highest molecular weight TMPE-OH (M_n = 1014 g/mol) resulted in a much faster time to minimum voltage than two lower molecular weight counterparts (M_n = 170 and 450 g/mol). We employed impedance spectroscopy to show that the AL comprising the highest molecular weight TMPE-OH exhibited the highest ionic conductivity, and differential scanning calorimetry to show that it also featured the highest dissolution capacity for the KCF₃SO₃ salt. This implies that the AL based on the highest molecular weight TMPE-OH exhibits the highest concentration of mobile ions, which in turn rationalizes its higher ion conductivity and the lowest minimum voltage in LEC devices.

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.

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.

Organic photovoltaic materials have reached power conversion efficiencies above 20%, yet their long-term operational stability remains a critical challenge. Processing conditions strongly influence molecular organization in the active layer, affecting orientation, intermolecular interactions, and ultimately the electronic structure of donor–acceptor systems. Understanding how these structural and electronic factors interrelate is essential for improving intrinsic photostability.

In this talk, I will present our recent work investigating the impact of processing on the electronic structure of high-performance organic photovoltaic materials using orbital-selective X-ray spectroscopy. Angular-dependent multi-edge NEXAFS measurements provide chemically selective insight into molecular orientation and depth-dependent organization in thin films. [1,2] By probing both carbon and heteroatom absorption edges, we disentangle the contributions of donor and acceptor components to the unoccupied electronic states.

Building on this structural and electronic understanding, we employ resonant photoemission spectroscopy to resolve the contribution of distinct chemical moieties to the valence electronic states. Resonant excitation enhances orbital selectivity, enabling chemically specific tracking of light-induced modifications in the occupied states. This approach provides direct insight into which molecular sites are particularly susceptible to photodegradation. Together, these approaches establish a chemically selective and orbital-resolved methodology for linking processing, electronic structure, and photostability in organic photovoltaic materials, offering guidance for the design of more robust active-layer systems.

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 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]

Printable organic solar cells are intrinsically interface‑rich: interfacial chemistry governs charge extraction, recombination, and durability, while optical design sets absorption and spectral selectivity. We develop a molecular “interface grammar” using self‑assembled monolayers (SAMs) to rationally control energetics and stability in non‑fullerene–acceptor OPVs. By tuning anchoring chemistry, conjugation, dipole orientation, and programmed SAM–BHJ interactions (π–π, quadrupolar), SAMs align work functions, improve wetting and molecular registry, suppress interdiffusion, and stabilize UV‑exposed contacts—enhancing carrier extraction, lowering non‑radiative losses, and extending operational stability [1]. Crucially, this same molecular logic is carried into manufacturing through azeotrope‑assisted SAM processing, which enables low‑temperature, printed p–i–n stacks with improved reproducibility and reduced solvent use—maintaining the interfacial benefits while meeting scalability and sustainability targets [2].

With robust OPV interfaces as the foundation, we then apply the identical SAM toolkit to the most fragile buried interface in perovskite/organic tandems: the interconnection layer (ICL), where imbalanced transport—especially inadequate hole transport in the organic subcell—causes voltage deficits and severe non‑radiative recombination. A hole‑transport SAM anchored to MoO₃ converts its inherently n‑type character to a p‑type surface; a SAM/MoO3/SAM sandwich further strengthens hole extraction, balances carrier transport, and suppresses interfacial recombination, yielding tandems with 26.05% PCE and Voc = 2.21 V (certified 2.216 V) and improved stability [3]. Finally, we close the loop between chemistry and optics: high‑throughput transfer‑matrix simulations coupled to genetic algorithms co‑design the multilayer stack around these SAM‑engineered interfaces, optimizing absorption–parasitic trade‑offs and tailoring spectra for semitransparent and color‑tunable devices [4]. Together, SAM‑programmed interfaces, solvent‑lean scalable processing, and data‑guided optical co‑design form a coherent pathway from durable, high‑efficiency OPV to promising hybrid tandem cells

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. 

Scalability and automation are critical for advancing organic solar cells (OSCs) toward high-throughput production, yet both remain significant challenges. In this presentation, I will introduce a simple yet effective strategy using Tz6T as a multifunctional additive to regulate ink-state pre-aggregation to address these issues. Tz6T interacts with both donor and acceptor molecules in the ink, enabling enhanced and more ordered pre-aggregation. This promotes uniform film formation and significantly reduces bimolecular recombination, achieving 16.4% efficiency in large-area green-solvent-processed OSC modules (19.3 cm²), ranking among the best reported values to date. Furthermore, the pre-aggregated ink mitigates morphology drift caused by time delays in pre-programmed robotic fabrication, yielding device efficiencies exceeding 16%, highlighting strong potential for high-throughput production. Beyond efficiency enhancement, Tz6T also improves long-term stability and demonstrates compatibility across diverse material systems, underscoring its broad applicability. This work provides a promising pathway toward sustainable, scalable, and automated fabrication of high-performance and stable OSCs, paving the way for their industrialization.

    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.