Organic photovoltaics (OPVs) represent a promising emerging technology for clean and renewable energy generation. Recent developments in the field of small molecule acceptors combined with an improved understanding of the device operation have propelled the power conversion efficiency (PCE) of OPVs to over 18 percent. However, further improvement in materials, processing and microstructural engineering of the photoactive layer, charge transport interlayers and cell architecture, would be required in order to attain the maximum theoretically predicted level of performance. In this talk I will discuss key recent developments in the field of OPVs with focus on practical strategies for boosting the overall cell performance. Particular emphasis will be placed on the use of electronic dopants and advanced interlayer technologies for improving the cell’s efficiency and operational stability.

OPV modules have a proven record efficiency of 12.6 % but a typical product efficiency of 5 – 7%. The first generation of OPV modules showed lifetimes of 5 - 10 years under outdoor conditions and product costs have come down from 10 €/Wp and are currently moving towards the 1 €/Wp regime. Forecasts anticipating the OPV technology at the GW level are predicting costs as low as 5 €ct/Wp [1].  This is the reason why organic modules were designed from the beginning of their product history to complement the classical PV portfolio. Applications such as power plants or roof top integration are of little relevance for OPV as long as the technology is still under development. Therefore, applications that are difficult to access for classical photovoltaic technologies are of high relevance. These make use of product properties such as transparency, integrability in surfaces, good indoor performance as well as high flexibility and low weight, but also flexible or digital production processes that allow the economic production of small production quantities or single-lot special designs. In summary, a central element of the OPV product is the design of flexible, colourful and semi-transparent products, which can be integrated into existing structures and fulfil requirements to operate applications with power requirements reaching from µWs up to MWs.

A significant improvement in operational stability would issue the most significant acceleration of OPV as a technology platform. Understanding lifetime limiting mechanisms in OPV is still at the beginning and is dominantly lacking reliable methods to uniquely identify degradation mechanisms within shortest time. Frist concepts to predict operational stability based on machine learning (ML) will be introduced in the 2^nd part of the talk.

Reducing non-radiative recombination of charge transfer (CT) state - appearing at the donor-acceptor interfaces in organic solar cells - is essential to achieve high fill factor (FF) and open circuit voltage (V_OC) in organic solar cells. Whereas the role of energetic disorder in such devices for charge generation is discussed extensively, the impact on non-radiative recombination is largely unexplored. The present study introduces a new understanding of organic solar cells with reduced non-radiative recombination losses. We show that combining high FF and V_OC is possible when non-radiative recombination of the CT state is supressed by reducing the energetic disorder. These findings open the route for the next prospect in the design of materials. This prospect asserts that intrinsic limit for the V_OC and FF of organic solar cells can be reduced compared with other photovoltaic technologies. This study provides a rationale to explain and further improve the V_OC and FF of organic solar cells, which is an essential step towards their commercialisation.

The high-performance OSCs with the optimal thickness of 100 nm are strongly related to the nanoscale formation of BHJ during and after the processing. However, upscaling of such devices from the laboratory to the industrial environment demands to increase the thickness of the photoactive layer to gain robust printing processes. However, this may lead to serious losses in the efficiency of NFA-based solar cells [1] due to enhanced recombination induced by longer transport paths towards the electrodes in combination with reduced electric fields inside the device. Nevertheless, under low light conditions, thick photoactive blends exhibit less space charge effects, leading to less recombination of the charge carriers [2] which is simply connected to less photon flux produced by low-intensity indoor illumination. Furthermore, transfer to the less toxic processing is an essential requirement for scalable deposition techniques such as roll-to-roll or other printing techniques usually combined with photoactive layers with more than 200 nm thickness [3,4]. Previously, we showed that the highly efficient solar cells with thick photoactive layers can be obtained by inkjet printing [5]. In this work, the non-halogenated ink formulation was applied to doctor-blade in air PM6:ITIC-4F-based blends. In order to further approach the industrial relevant processing conditions, another promising wide band-gap polymer PTQ-10[6] was exploited due to the low cost, solubility in non-halogenated solvents [7], high efficiency, and thick layer potential processing of this material [6,8]. Identical ink formulations using o-xylene: tetralin mixture were applied to PTQ-10:ITIC-4F blends allowing to compare the performance of corresponding solar cells using thick blends as a function of donor polymer as well as thermal post-treatment. The photovoltaic properties of the solar cells were studied under two light sources, i.e. simulated AM 1.5G and indoor light at 200 Lux and 1000 Lux, to learn more about recombination losses in OSC using thick blends. Under optimal processing conditions, PM6:ITIC-4F blends produce solar cells with a PCE of 9.3 % for 300 nm thick layer under 1 sun illumination, respectively, while the use of thicker blend layers leads to lower efficiencies. In contrast, solar cells based on PTQ-10:ITIC-4F blends showed the highest PCE for 500 nm thick layer with a PCE of 11.3 % under 1 sun illumination and 15.71% under indoor light at 200 Lux.

We present an approach to predictive modeling of organic photovoltaic systems that connects quantum mechanical treatments of electronic structure with the classical physics required to describe mesoscopic spatiotemporal scales.

The approach leverages the Martini coarse-grained model for the modeling of the morphology, thus incorporating chemical specificity while providing access to mesoscopic scales [1]. Martini-based coarse-grained molecular dynamics simulations are used to generate morphologies taking into account the processing conditions, such as solution processing and thermal annealing [2]. Given that such coarse-grained models retain a sizable degree of chemical specificity, the morphologies can be directly back-mapped to atomistic resolution. This allows not only to probe the impact of chemical modifications of the molecular structure on the resulting morphology, but also to gain access to electronic structure information while taking into account the large-scale self-organization process of the thin film [2,3].

As an application, we show how the approach can be used to probe the impact of polar side chains on electronic and structural properties of organic photovoltaic blends [3]. We find that the introduction of polar side chains on a similar molecular scaffold does not affect molecular orientations at interfaces. Such orientations are instead found to be strongly affected by processing conditions (i.e., thermal annealing) and polymer molecular weight. We find that polar side chains, instead, impact significantly the energy levels of the organic blend, causing broadening of these levels by electrostatic disorder.

Finally, we will conclude with a brief discussion of extensions of the approach, including coupling to machine learning techniques to enable higher-throughput characterization of the simulations, one aspect that is paramount to enable computer-aided materials design.

The record efficiencies for organic solar cells were increased strongly over the past few years due to significant advances in organic semiconductor materials, especially the replacement of fullerenes with mostly linear molecular acceptor materials, known as Non-Fullerene Acceptors. The improvements stem from broadening the absorption spectrum by strong and complementary absorption of donor and acceptor and simultaneously reducing the voltage loss due to charge carrier transfer between donor and acceptor significantly. Using the material combination D18:Y6, an independently confirmed efficiency of >18% was achieved [1]. After the materials were made available by several companies, we achieved the certified world record on 1cm² using this material at 15.24% efficiency [2, 3]. Recently we also fabricated a minimodule with laser ablation for the patterning, achieving 13.94% certified efficiency, which is as well slightly higher than the value of 13.6% which had set very recently the new record in the last version of the efficiency tables [4]. We will report on how this record was achieved and further optimization potential. These record values are important to highlight the potential of the OPV technology and closing in towards 20% efficiency will undoubtedly justify further and intensified work. Besides this, we as well develop device stacks and module concepts which aim at low-cost, high-volume production of efficient and longterm-stable OPV using roll-to-roll coating and printing. We will report on our ITO-free approach based on a metallized barrier substrate, where we achieved efficiencies up to 12% using PM6:DT-Y6 from non-chlorinated solvents on lab scale devices and up to 6.2% efficiency for fully R2R coated and printed ITO-free OPV-modules with an area of nearly 800cm².  

Non-fullerene acceptor-based ternary organic solar cells have demonstrated better photo charge generation than their binary counterparts.^[1] But, underlying photophysics and the trade-off between complementary absorption and the energy offset between donor and acceptor(s) on the charge generation is not fully understood. This understanding is critical for material synthesis and device design.^[2] In this work, we utilize ultrafast laser spectroscopy technique to study the charge generation in several NFA-based ternary blends with the polymer donor PM6. The selective excitation of PM6 leads to ultrafast singlet exciton energy transfer to the NFAs, outcompeting electron transfer. Subsequently, singlet excitons in the NFA undergo hole transfer to the donor, resulting in free charge generation. This requires sufficient ionization energy offset between donor and acceptors to ensure efficient free charge generation. While broad absorption spectrum is important for photon collection, but having sufficient ionization energy offset is crucial for charge generation and hence the quantum efficiency in ternary organic solar cells.

Organic photovoltaic (OPV) devices have recently experienced a fast rise in power conversion efficiency (PCE) with the introduction of non-fullerene acceptor (NFA) molecules, reaching above 18 % PCE today, placing device stability as the main focus area for this technology. Transition metal oxides have been demonstrated as an important class of materials for OPV devices, where they serve as charge carrier selective interlayers for efficient electron and hole extraction. In organic photovoltaics (OPV), the introduction of the high-performing non-fullerene acceptors has set new requirements on the embedded interlayers, as e.g. new interlayer related instabilities have recently been reported, making a thorough understanding of such interface effects highly important for the further development of this field and technology.

In this presentation, recent progress made within sputtered metal oxide electron [1,2] and hole [3] transport interlayers for thin film organic photovoltaics is presented. Supported by a variety of surface science characterization techniques, the role of e.g. microstructure, work function, oxygen vacancies and energy band alignment, on the performance of such interlayers in organic photovoltaic devices is discussed. This includes a focus on their positive impact on non-fullerene acceptor based OPV device stability, as compared to conventional metal oxide interlayers. Here, new results focusing on the integration of 2D materials in NFA OPV will also be elaborated on. Finally, an outlook addressing up-scaling of such metal oxides for new OPV applications will be presented.

M. Mirsafaei, P. B. Jensen, M. Ahmadpour, H. Lakhotiya, J. L. Hansen, B. Julsgaard, H.-G. Rubahn, R. Lazzari, N. Witkowski, P. Balling and M. Madsen, “Sputter-deposited titanium oxide layers as efficient electron selective contacts in organic photovoltaic devices” ACS Appl. Energy Mater., 3, 253 (2020)

D. Amelot, M. Ahmadpour, Q. Ros, H. Cruguel, N. Casaretto, A. Cossaro, L. Floreano, M. Madsen and N. Witkowski, “Deciphering electron interplay at the fullerene/sputtered-TiOx interface: a barrier-free electron extraction for organic solar cells” ACS Appl. Mater. Interfaces, 13, 19460 (2021)

M. Ahmadpour, A. L. F. Cauduro, C. Méthivier, B. Kunert, C. Labanti, R. Resel, V Turkovic, H.-G. Rubahn, N. Witkowski, A. K. Schmid and M. Madsen ^“Crystalline molybdenum oxide layers as efficient and stable hole contacts in organic photovoltaic devices” ACS Appl. Energy Mater. 2, 420 (2019)

Polymer solar cells (PSCs) are among the most promising approaches toward low-cost environmentally sustainable and renewable photovoltaic devices. The insufficient stability is still a limiting factor for commercialization of PSCs and one of the key challenges of PSC technology. In PSCs based on fullerene acceptors, the thermal stability at high temperatures is affected by the diffusion of fullerenes inside the donor and the phase separation via Ostwald ripening mechanisms. The nanoscale morphology and thermodynamic stability in polymer blends are ultimately governed by miscibility of donor and acceptor (in the selected solvents and processing conditions). Predicting miscibility and stability is a formidable challenge that requires deeper fundamental understanding on polymer blends thermodynamics.

In this talk we discuss the application of large-scale atomistic methods for the modeling of polymer blends and for the prediction of their stability through the application of the Flory-Huggins theory[1]. We focus on the interesting case of PTB7 small band gap polymers that have been used to synthesize ultrastable PTB7:PC70BM blends for efficient PSCs[2]. The observed thermodynamic stability with the suppression of the thermally activated fullerene diffusion, is explained in terms local minima of the mixing enthalpy versus fullerene concentration. [2].

We also discuss results related to ternary blends with the sensitizer Si-PCPDTBT added to blends of PTB7 (or PTB7-th) donor polymers and fullerene acceptor PC71BM[3]. In addition to the dependence on fullerene concentration we find that the mixing enthalpy is strongly affected by the blend density. This outcome is relevant to model out-of-equilibrium conditions during which density fluctuations are expected and provides information on the preferable morphology of the sensitizer in the blend. We finally discuss perspectives and theoretical challenges for the atomistic modeling of polymer blends and for the reliable prediction of stability and thermodynamic properties.

With the emergence of indoor photovoltaics as a possible application for organic solar cells, new design criteria are developed to facilitate optimum performance under indoor light sources such as light emitting diodes and low light intensities.[1] For instance, a high parallel resistance is more relevant than under 1 sun illumination. Such a high parallel resistance is typically realized by a thick absorber layer to avoid leakage currents.[2] However, organic solar cells with thick active layers are often limited in their performance by space-charge effects caused by doping, asymmetric carrier mobilities or charged trap states.[3, 4] The latter effect is not well understood yet even though shallow defects are commonly found in organic solar cells due to their intrinsic energetic disorder. Thus, we present a theoretical analysis of the influence of photo-induced space charge evoked by energetic disorder on the performance of organic solar cells under indoor conditions.[5] Drift-diffusion simulations enable us to watch space charge build up in shallow defects with increasing light intensity. Also, we observe that the performance of organic solar cells is less sensitive to high levels of energetic disorder under low light operation than under solar irradiation since the density of space charge increases with light intensity. As a consequence, experimentalists should not quickly discard material systems that perform badly under standard test conditions due to energetic disorder as they still could be viable candidates for indoor application.

In recent years the development of new NFA molecules has been increasing performances and competitiveness. The new generations of NFAs offers tremendous advantages, like extended absorption ranges, better complementarity with polymers absorption, optimized blend morphologies and miscibility, along with better charge transport and exciton splitting properties. Despite showing efficiencies above 18% (1) the industrial transfer of OPV devices and their penetration to the market remains low, principally due to the need of improving industrial processes and long-term stability. On these days some of the new families of molecules seems to be very promising for industrial transfer. New generation of NFAs focus more on enhance efficiency, the Y6 molecule for example, shows an impressive efficiency of 15% (3), but this molecule is only soluble in halogenated solvents. Subsequent studies succeeded in solubilizing the molecule in non-halogenated solvents with 16% efficiency and similar results for blade coating fabrication.(4) However, stability tests and industrial transfer are still missing for this type of molecules. On this regard, it appears crucial to develop materials compatible with industrial requirements and intrinsically stables in parallel with their performances.

Today, a large library of building blocks is available to prepare NFAs with tunable optical and electronic properties. For the optimization of the performances in solar cells, it is necessary to focus on the development of narrow band gaps NFAs with a broad and intense absorption in the visible range and suitable LUMO energy level to maximize the open-circuit voltage (V_oc), but additionally, they should demonstrate high stability and non-halogenated solvents compatibility for industrial use. Keeping in mind this requirement, we propose a molecular design inspired by ITIC molecules with an extended electron-donating core and functionalized with solubilizing groups. We synthesized and characterized a series of four NFAs called BITIC-C8, BITIC-PhC6, BITIC-PhC6F4 and BITIC-C8F4 based on an 4,9-dihydro-s-indaceno[1,2-b:5,6-b']dithiophene (IDT) central core.(5) The influence of the nature of the solubilizing groups and the presence of fluorine atoms on properties and performance of the molecules, was investigated. Interestingly, we observe increased photo-stability of the molecules in thin films, compare to reference ITIC. The photovoltaic performances of the four NFAs were assessed in binary blends using PM6 as the donating polymer and in ternary blends with ITIC-4F. Solar cells show power conversion efficiencies of up to 11.1% in ternary blends processed from non-halogenated solvents and without any thermal post-treatment, making this process more compatible with industrial requirements.(5)

Understanding the role that exciton diffusion plays in organic solar cells is a crucial to understanding the recent rise in power conversion efficiencies brought about by non-fullerene

acceptors (NFAs) [1].  In this presentation I will discuss the role that exciton diffusion plays in efficient charge generation.

Firstly, I will outline how one can measure the exciton diffusion lengths through quenching experiments using time resolved photoluminescence, and through exciton-exciton annihilation (EEA) using high resolution TRPL [2]. I will then introduce a novel technique, coined pulsed-PLQY, to measure the diffusion length through EEA without the need for any temporal measurements, greatly increasing the speed and ease of the measurement while reducing the operational costs.

Traditional and pulsed-PLQY EEA techniques are simulated using a Kinetic Monte-Carlo approach and the limits of both techniques are discussed. It is found that pulsed-PLQY is less sensitive to the choice of excitation density and has increasing confidence with increasing densities measured. The simulations are validated by performing both experimental techniques on organic thin films, reproducing the predicted trends. Pulsed-PLQY is then used to measure the diffusion length in a range of organic semiconductors, including technologically relevant NFAs. We find that the NFAs show an increase in diffusion length, driven by an increase in diffusivity, compared to a benchmark fullerene acceptor [3].

The globally growing market of smart applications and devices in a society which aims for sustainability and eco-friendliness leads to the question of powering all these systems. Powering and enabling their long-term self-sufficiency results in an increasing interest in (micro) energy harvesting solutions, from sources such as temperature differences, vibrations and light. In the special case of powering indoor devices with artificial (narrow) light spectra organic solar cells and modules have emerged as a promising photovoltaic technology which combines low fabrication cost, lightweight and mechanical flexibility. Most of the work focused on the development of new and specially tailored semiconductor materials (optimal bandgap of ~1.8eV) on the classical Indium Tin Oxide (ITO)-based architecture with the known issues related to that (mechanical brittleness, rare material/environmental impact, stability, roll-to-roll (R2R) compatibility). [1]

Herein we present ITO-free organic photovoltaic (OPV) cells and modules processed from non-halogenated solvents with high parallel resistance which enables their usage at extremely low intensities as 100 lux. The upscaling process from 0.1 cm² cells to 7.3 cm² modules (8 cells in series) was successfully done with performance losses less than 15 % relative. Under 500 lux our modules show an efficiency of 14 %. This is, to the best of our knowledge, the highest value reported for ITO-free non-fullerene acceptor OPV modules processed from green solvents. We can show that the ITO-free, R2R compatible electrode system is applicable to a wide range of modern organic semiconductors used in OPV technology. Furthermore, the presented ITO-free electrode system and cells stack work on rigid as on flexible substrates which increases the versatility of use cases. Surprisingly, novel donor:acceptor systems designed for sunlight application yield similar results under dim indoor light because of their outstanding external quantum efficiency, resulting in higher currents thus compensating for their typically lower band gap. However, these absorber materials are inferior in terms of their theoretical maximum performance. We also will address the influence of different light colours (warm white to cool white) on the efficiency.

Organic solar cells have great potential application in wearable electronics due to the advantages of flexible, light-weight, colorful and roll-to-roll compatible. Printable materials and inks are the materials basics regarding the printing fabrication of the organic solar cells. Large-area homogenous and low-thickness dependent printed films would ensure high reproducibility of the large-area devices. On the bases of these two points, a series of printable interface materials from functional grafting modification, organic-inorganic hybrid modification, crystalline and amorphous hybrid modification were developed, which showed high work thickness up to 200 nm, large thickness tolerance, excellent thin films quality, and as well as good photoelectronic properties. In addition, we developed large-area electrodes and interface layers using gravure printing. With these, the efficiency of 1 and 9 cm² flexible organic solar cells has reached above 16% and 14%.

Organic photovoltaics have a huge potential to decrease the environmental impact of electricity generation and over time enable lower cost PV. As a first step on the technology and market development of OPV, the Swedish company Epishine is focusing on the indoor PV market (IPV). The demand for connected sensors is increasing and the cost for battery replacements are a limiting factor. A credit card sized organic IPV module can replace the need for batteries or extend the battery life time. In this talk co-founder and CTO Jonas Bergqvist will give a brief introduction to IPV, give an update of the present status of Epishine and discuss the technology development at Epishine and what is important for further improvment of organic IPV.

X. Rodríguez-Martínez¹, E. Pascual-San José¹, Zhuping Fei², A. Sanchez-Díaz¹, A. Harillo¹,  M. Heeney², R. Gimerà³, M. Campoy Quiles¹

¹Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Spain

²Chemistry Department, Imperial College London, UK

³Universitat Rovira I Virgili, Spain

While the strong performance increase in organic photovoltaics is driven by the synthesis of improved materials, the highly entangled thickness-composition-morphology parameter space makes almost impossible the prediction of performance for new systems. One notable exception is the thickness dependence of the active layer, which was formulated in a seminal paper from 1999 [1]. On the other hand, the dependence of the device performance on donor/acceptor ratio has thus far been more elusive; despite composition being one of the parameters that affects efficiency more strongly. In order to address this complex problem, in this talk we will present the results of feeding high-throughput experimental methods into artificial intelligence algorithms in order to predict the composition-performance landscape.

We will first describe a novel methodology for the fast evaluation of donor/acceptor systems for photovoltaics. The new approach is based on the fabrication of samples with gradients in the relevant parameters of interest that represent a large fraction of the corresponding parameter space. In particular, we fabricate gradients in thickness, microstructure, composition and apply hyperspectral imaging to correlate material and device properties. The method is up to 100 faster than conventional optimization protocols, uses less than 50 mg of each active layer material and generates hundreds to millions of data points per system [2,3].

Then we show how this machinery can be used to find design rules for the optimum composition in non-fullerene acceptors based devices. For this, the combinatorial evaluation of more than 15 donor/acceptor systems -which generates thousands of data points in the thickness/composition parameter space-, is coupled to machine learning algorithms. Trained algorithms can predict the composition for maximum efficiency, and even reproduce multi-maximum efficiency vs composition diagrams, from basic material inputs, such as energy levels and optical and electrical traits [4].

Photoluminescence originating from the recombination of electrons and holes within the absorber layers in solar cells is an important characterization technique for many photovoltaic technologies as it provides direct information about the separation of the quasi Fermi levels (QFL) inside the device. The photoluminescence (PL) in organic donor/acceptor (D/A) systems is typically dominated by local excitons which decay radiatively before dissociation into free charge carriers at the D/A interface. Thus, this (major) part of the PL signal neither correlates with the separation of the QFL nor with the operational state of the device. In contrast, during electroluminescence (EL) experiments electrons and holes are injected in their respective material phases directly and recombine pairwise at the D/A interface (partially radiatively). Therefore, the EL radiation is proportional to the product of electron and hole concentrations and thus directly to the QFL separation. In this work, we determine the time resolved QFL separation during charge carrier decay from transient EL within the absorber of high-efficiency organic solar cells, compare it to the externally measured voltage at the contacts and demonstrate the applicability of this method for a wide range of injection currents. We further show the potential of this measurement technique to get direct insights in the recombination dynamics of electrons and holes within organic D/A materials.

The device performance of organic bulk heterojunction (BHJ) solar cells is ultimately derived from processes taking place between excitons, charge-transfer (CT) states, and free charge carriers. In fullerene-acceptor-based BHJ systems, characterized by large donor-acceptor energy level offsets, the photovoltage is typically limited by the energetics and kinetics of CT states.[1] However, this picture has been challenged with the emergence of nonfullerene-acceptor-based systems with low energy offsets,[2] where the role of excitons becomes important. In this work, the interplay between excitons, CT states and free charge carriers is investigated.[3] Based on detailed balance considerations, we derive an analytical framework describing the photocurrent quantum yield, the charge-carrier recombination rate constant, and the open-circuit voltage in low-offset BHJ systems. Furthermore, the essential conditions for mutual equilibrium between the different species to occur are clarified. Finally, we find that the photovoltaic parameters are not only limited by the energetics but also critically determined by the relative kinetics between the different species. These findings provide insights into the operation of state-of-art non-fullerene organic solar cells with low offsets, paving the way for power conversion efficiencies exceeding 20%. 

With the fast development of efficiency of organic solar cerlls, performance decay dynamics and detailed degradation mechanism of polymer solar cells become the next most important research topic for organic solar cells. Several research groups have been intensively worked on the degradation and stability of polymer:fullerene solar cells, and various degradation pathways were clarified, including: photon induced dimerization of fullerene molecules[1,2] and interfacial degradations.[3] Unlike fullerene based solar cells, our recent research results revealed that photon induced interfacial degradation of the non-fullerene molecules is the main pathway for the performance decay of polymer:non-fullerene soalr cells.[4-5] In this presentaion, we will present the latest resutls in this topics.

Scaling effects of OPV devices for large-area solar cells and indoor applications

Gregory Burwell¹, Wei Li¹, Oskar J. Sandberg, Paul Meredith¹, Ardalan Armin¹

¹Sustainable Advanced Materials (Sêr-SAM), Department of Physics, Swansea University, Singleton Park, Swansea SA2 8PP, United Kingdom

Abstract

Organic photovoltaic (OPV) devices have demonstrated steadily improving figures in merit in recent years, principally due to the development of non-fullerene acceptor (NFA)-based materials. However, superlative OPV devices are invariably lab-scale and small (< ~ 0.1 cm²) and it has proven challenging to replicate high power conversion efficiencies at practical sizes. At light intensities close to 1 Sun, the sheet resistance of available monolithic transparent conductive oxide (TCO) materials limits the performance of these larger devices. However, indoor OPV (IOPV) devices are required to operate at low light intensities, and thus demonstrate different area-scaling behavior. In contrast to 1 Sun operation, the performance of large-area IOPV devices are much less affected by the sheet resistances of transparent conductive electrodes, but instead by the shunt resistance, at low light intensities. In this work, we examine key parameters for improving the efficiency of large-area  devices under different illumination regimes using drift-diffusion and finite element modeling. We examine application-specific device optimization of OPV devices for IOPV and standard 1 Sun operation reviewing aspects such as the transparent conductive electrode, material selection, and fabrication considerations.