Solution sequential deposited organic photovoltaics: From morphology control to large-area modules

Organic optoelectronic materials enable cutting-edge, low-cost organic photodiodes, including organic solar cells (OSCs) for energy conversion and organic photodetectors (OPDs) for image sensors. The bulk heterojunction (BHJ) structure, derived by blending donor and acceptor materials in a single solution, has dominated in the construction of active layer, but its morphological evolution during film formation poses a great challenge for obtaining an ideal nanoscale morphology to maximize exciton dissociation and minimize nongeminate recombination. Solution sequential deposition (SSD) can deliver favorable p–i–n vertical component distribution with abundant donor/acceptor interfaces and relatively neat donor and acceptor phases near electrodes, making it highly promising for excellent device performance and long-term stability. Focusing on the p–i–n structure, this review provides a systematic retrospect on regulating this morphology in SSD by summarizing solvent selection and additive strategies. These methods have been successfully implemented to achieve well-defined morphology in ternary OSCs, all-polymer solar cells, and OPDs. To provide a practical perspective, comparative studies of device stability with BHJ and SSD film are also discussed, and we review influential progress in blade-coating techniques and large-area modules to shed light on industrial production. Finally, challenging issues are outlined for further research toward eventual commercialization.