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Solution-processed organic solar cells (OSCs) have becoming a promising photovoltaic technology for a low-cost electricity generation. However, poor stability of OSCs is still a severe problem need to be understood and solved for future application. In this work, we conducted an air stability study for both fullerene and non-fullerene based OSCs. As a result, the degradation mechanism was found different for these two types of OSCs. The Urbach energy determined from the EQE measurement indicates that the air-degradation in fullerene based OSCs is mainly ascribed to its increased energetic disorder. Differently, the photoluminescence (PL) measurement implied that the air-degradation in non-fullerene based OSCs mainly results from the degraded charge dissociation and energy transfer ability. Therefore, different stability improving strategy will be needed for fullerene and non-fullerene based OSCs in future.

PEDOT:PSS has been widely used as a hole conductive polymer due to its high conductivity and transparency, which is ideal for thin film solar cell with large-scale printing processability. We demonstrated a simple way to enhance the efficiency and reproducibility of PEDOT:PSS-based normalstructure perovskite solar cells. Metal oxide MoO 3 layer has been thermal-evaporated onto PEDOT:PSS as a surface passivation layer. The PCE of perovskite solar cell has been enhanced by 18% after MoO 3 passivation and the short circuit current density (J sc ), open circuit voltage (V oc) and fill factor (FF) has been improved simultaneously. The performance enhancement of MoO 3 modified PSCs is attributed to the reduced current leakage, enhanced hole extraction characteristics, and mitigated the trap-assisted interfacial recombination.