Scalable fabrication of organic solar cells based on non-fullerene acceptors

Organic solar cells have recently experienced a substantial leap in power conversion efficiency, in part driven by formulations with new non-fullerene acceptors. This has brought the technology past the psychologically important mark of 15 % efficiency for unscaled laboratory devices, and the results are stimulating another burst of research activity. Whether this will propel the technology into a viable commercial contender has yet to be determined, but to realize the potential of organic solar cells for utility scale application, fabrication using scalable processing techniques has to be demonstrated - otherwise, the passing of the 15 % mark will eventually leave no more lasting impact than what the passing of the 10 % mark did. Thus, addressing the scaling lag between the 15 % cell efficiencies of lab-scale devices on rigid glass substrates fabricated using non-scalable techniques and the 7 % efficiencies of scalably fabricated devices on flexible substrates is key. Here, we discuss the concept of scalability and give an account of the literature on non-fullerene acceptor devices fabricated with scalable methods and materials. On the basis of this, we identify three crucial focus points for overcoming the lab-to-fab challenge: i) dual temperature control, i.e. simultaneous control of the ink and substrate temperatures during deposition, ii) systematic in situ morphology studies of active layer inks with new, green solvent formulations during continuous deposition, and iii) development of protocols for continuous solution processing of smooth, transparent interfacial layers with efficient charge transfer to the active layer. Combining these efforts and in general accompanying such studies with stability analyses and fabrication of large-area, scalably processed devices are believed to accelerate the relevance of organic solar cells for large-scale energy supply.