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All-solution-processed organic photovoltaic (OPV) cells allow cost- and energy-effective fabrication methods for large-area devices. Despite significant progress on laboratory-scale devices, there is still a lack of interface materials that can be solution processed on top of the active layer, are compatible with novel non-fullerene acceptors (NFAs), and also provide sufficient long-term stability. We developed a novel interface layer concept, where alcohol-based organic polymer nanoparticles can be processed on top of a polymer-NFA active layer and doped to achieve a quasi-Ohmic hole contact. Moreover, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is processed as a second layer, forming a bilayer solution-processed hole transporting layer (HTL), providing an industrially relevant inverted architecture with a protective PEDOT:PSS layer on top. Most importantly, exceptional stability is observed. PM6:Y6 devices with the bilayer HTL are demonstrated to maintain 93% of their initial efficiency for 1,800 h under continuous solar cell operation at 60°C.

Although the power conversion efficiencies (PCEs) of bulk heterojunction (BHJ) organic solar cells (OSCs) continue increasing toward the 20% milestone, important factors for industrial application are mostly neglected, such as photostability and cost potential. Single-component OSCs (SCOSCs) employing materials with chemically bonded donor and acceptor moieties successfully overcome the immiscibility between the donor and the acceptor as well as the resultant self-aggregation under external stress. To inspire a broader interest, the industrial figure of merit (i-FoM) of BHJ OSCs and the corresponding SCOSCs is calculated and analyzed, which includes PCE, photostability, and synthetic complexity (SC) index. Despite having a slightly more complex synthesis, all SCOSCs exhibit increased i-FoM values compared with the corresponding BHJ OSCs, and with the increase in efficiency, SCOSCs possess further potential for a higher i-FoM value. With the excellent photostability of nearly all investigated single-component semiconductors, SCOSCs are coming into the focus of attention for industrial utilization.

While wavelength-dependent photodegradation of organic solar cells (OSCs) under visible light is typically discussed in terms of UV/blue light-activated phenomena, we recently demonstrated wavelength-dependent degradation rates up to 660 nm for PM6:Y6. In this study, we systematically investigated this phenomenon for a broad variety of devices based on different donor:acceptor combinations. We found that the spectral composition of the light used for degradation, tuned in a spectral range from 457 to 740 nm and under high irradiances of up to 30 suns, has a crucial influence on the device stability of almost all tested semiconductors. The relevance of this phenomenon was investigated in the context of simulated AM1.5 illumination with metal halide lamps and white LEDs. It is concluded that the current stability testing protocols in OSC research have to be adjusted to account for this effect to reveal the underlying physics of this still poorly understood mechanism.

Most interface materials for organic solar cells (OSCs) were originally optimized for fullerene-based systems and are now being adapted for non-fullerene acceptor (NFA) based solar cells. This reliance on established interface materials results in a limited choice of interface materials for NFA based OSCs. For vacuum processed organic devices, the concept of doped interface materials is exceptionally successful, but has not yet been translated to modern NFA based devices due to solution processing constraints requiring orthogonal solubility. Herein, we report a novel concept for the development of solution-processed HTL in inverted n-i-p architecture OSCs using doped organic nanoparticles (D-NPs), overcoming solvent compatibility limitations and enabling scalable production processes. We demonstrate that the functional key interface properties of D-NPs HTLs can be tailored independently over a wide regime. Specifically, conductivity and work function can be optimized separately by varying the dopant concentration and the material system. By using D-NPs as HTL in the n-i-p architecture, power conversion efficiencies (PCE) of over 12 % are achieved for PM6:Y6 based devices. The D-NPs HTL concept is successfully applied to a variety of organic semiconductors used in photovoltaics and opens a new class of tailorable interface materials for solution-processed HTL materials.

Morphological control over the bulk heterojunction (BHJ) microstructure of a high-efficiency small molecule photovoltaic system composed of a quinquethiophene based molecule (DRCN5T) as electron donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM) as electron acceptor is demonstrated using three different post-processing strategies, including thermal annealing (TA), solvent vapor annealing (SVA), and two-step annealing (TA-SVA) treatments. We systematically analyze the processing condition-microstructure-device property relationships, explore the corresponding morphology evolution and their effects on carrier transport and recombination dynamics in BHJs as well as understand the nature of phase-separation process resulting in light-induced degradation mechanisms. Within the investigated results, the causative relations between annealing sequence, photovoltaic parameters, morphology evolution and charge carrier dynamics are for the first time delineated. In addition, the observed trade-offs in device efficiency and stability with respect to the well-defined morphologies are highlighted. The in-depth picture of the bulk microstructure formation and its kinetic evolution as a function of the specific post-processing approaches is a valuable asset for the design of new photovoltaic materials and thin film nanoscale architectures that are more efficient and better aid future commercialization efforts.

Simultaneously enhancing device performance and longevity, as well as balancing the requirements on cost, scalability, and simplification of processing, is the goal of interface engineering of organic solar cells (OSCs). In our work, we strategically introduce antimony (Sb3+) cations into an efficient and generic n-type SnO2nanoparticles (NPs) host during the scalable flame spray pyrolysis synthesis. Accordingly, a significant switch of conduction property from an n-type character to a p-type character is observed, with a corresponding shift in the work function (WF) from 4.01 ± 0.02 eV for pristine SnO2NPs to 5.28 ± 0.02 eV for SnO2NPs with 20 mol. % Sb content (ATO). Both pristine SnO2and ATO NPs with fine-tuned optoelectronic properties exhibit remarkable charge carrier extraction properties, excellent UV resistance and photo-stability being compatible with various state-of-the-art OSCs systems. The reliable and scalable pristine SnO2and ATO NPs processed by doctor-blading in air demand no complex post-treatment. Our work offers a simple but unique approach to accelerate the development of advanced interfacial materials, which could circumvent the major existing interfacial problems in solution-processed OSCs.