What Makes Thickness‐Tolerant Organic Solar Cells?

Abstract Relatively thick‐film organic photovoltaics (OPVs) are desirable to spark commercialization through mass‐printing methods. Thickness‐resilient donor:acceptor blends are, however, scarce and not fully understood. The interplay between electronic, optical, and microstructural properties of the photoactive layer (PAL) generates a multi‐parametric space where rationalization is far from trivial. In this work, high‐throughput experimentation, simulations, and machine learning (ML) methods are leveraged to provide material and device insights toward thickness‐resilient OPVs. From a database of 720 inverted devices and 20 different donor:acceptor blends, two main blend families are identified in terms of their resilience against increased PAL thickness (>200 nm). These are archetypically represented by PBDB‐T:ITIC (thickness‐sensitive) and PTQ10:Y6 (thickness‐resilient). Kinetic Monte Carlo (kMC) simulations elucidate that the blend morphology alone, either in the form of an effective medium or energy cascade, can explain the experimental short‐circuit current density and open‐circuit voltage trends without tweaking the recombination parameters (cf. drift‐diffusion, DD). High fill factors (FFs) in thick‐film devices cannot, however, be reproduced by the kMC or DD simulations. ML models show that complementary absorbing donors and acceptors (shifted absorption onsets) mixed in balanced weight ratios provide a favorable hole back‐transfer efficiency to increase the FF in thick‐film devices.