An organic cathode for low-temperature processed, flexible ternary organic solar cells with high-performance

In this study, we developed a flexible cathode for fabricating high-performance ternary organic solar cells (OSCs). With solvent engineering and acid treatment, the conductivity of the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) electrode was significantly enhanced with the sheet resistance reduced from 1081 to 83 Ω sq^-1. After being coated with polyethylenimine, work function of the PEDOT:PSS electrode was tuned from -5.07 to -4.12 eV, which is beneficial for electron collection in OSCs. With this technique, the OSCs (on glass) showed an average power conversion efficiency (PCE) of 16.3%, which is comparable to that of conventional inverted OSCs with commonly used indium-tin oxide and sol-gel-processed zinc oxide. However, the processing temperature of the inverted OSCs was dramatically lowered from 200 to 120 °C. The flexible OSCs (on polyethylene naphthalate/PEDOT:PSS/PEIE) exhibited a high PCE of 14.1%. After being bended for 300 cycles, the PCE was only degraded by 8.5%, indicating the excellent bendability of the flexible OSCs with the organic cathode.