Solution-Processed Co₃O₄-Based Hole Transport Layer for Nonfullerene Organic Solar Cells

The imperative for achieving commercial success in organic solar cells (OSCs) lies in their efficient and stable operation within open-air environments, which enables large-scale production while concurrently reducing manufacturing costs. Poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) is usually used as a hole transporting material in the conventional configuration of OSCs; however, the observations reveal inferior stability due to its acidic and hygroscopic tendency. Therefore, introducing a hole transport layer (HTL) for replacing PEDOT:PSS is essential for OSCs. This work highlights both these issues; a simple and low-cost solution-processed Co 3 O 4 HTL was developed for nonfullerene-based OSCs in open-air conditions. The cobalt(II) acetate tetrahydrate (CATH) and adipic acid precursors were used to synthesize the Co 3 O 4 HTL under ambient conditions through one-shot mixing. To control the electronic properties of the Co 3 O 4 HTL thin film, thermal annealing (TA) and UV–ozone (UVO) post-treatment were employed. OSCs with the Co 3 O 4 HTL afford an excellent power conversion efficiency of 14.13% for the PM6:Y6 absorber layer, which is much higher than that of the control PEDOT:PSS (12.62%) and CATH (13.01%) counterpart. Interestingly, the derived Co 3 O 4 HTL-based OSC exhibited higher stability with the continuous illumination of AM1.5G lights under ambient conditions. In conclusion, this work emphasizes the pivotal role of solution-processed Co 3 O 4 -based HTLs in advancing the efficiency and stability of nonfullerene OSCs, contributing to the advancement toward efficient and sustainable photovoltaic technologies.