High open-circuit voltage and short-circuit current flexible polymer solar cells using ternary blends and ultrathin Ag-based transparent electrodes

Sputtered ultrathin silver-based multilayer electrodes have emerged as promising ITO-free candidates for lightweight, roll-to-roll processable flexible organic photovoltaics due to their high conductivity, low parasitic absorption, and excellent mechanical flexibility. However, Ag-based flexible solar cells normally yield inferior device performance when compared to conventional glass/ITO analogues. In this work, we report the use of a two-resonance tapping cavity (TRTC) based transparent electrode for achieving high-performance flexible PBDBT:ITIC solar cells. To reach optimal light harvesting without significantly sacrificing the high open-circuit voltage, the non-fullerene acceptor was partially substituted by PC₇₁BM to transform the binary blend into a ternary blend. The combination of open-circuit voltages as high as 0.88 V with short-circuit currents close to 18 mA cm^-2 leads to power conversion efficiencies higher than 11% for optimal TRTC rigid cells under AM 1.5G 1-sun illumination. Remarkably, when the TRTC was integrated onto flexible PET substrates, a 10.6% efficiency was achieved for the cells, while a robust mechanical flexibility was preserved. This is the highest efficiency value ever achieved for flexible organic solar cells.