An Easily Accessible Cathode Buffer Layer for Achieving Multiple High Performance Polymer Photovoltaic Cells

Here we report a successful efficiency improvement strategy in both conventional and inverted polymer solar cells (PSCs) based on multiple polymer blends, using a feasible and commercially available cathode buffer layer (CBL), namely barium hydroxide [Ba(OH) 2 ], to modify the photoactive blend and cathode contacts. High performance PSCs with an identical Ba(OH) 2 buffer layer were fabricated based on the multiple light-harvesting PBDT-TS1:PC 71 BM, PffBT4T-2OD:PC 71 BM, and PBDT-TS1:N2200 blends. The conventional PSC with Ba(OH) 2 as the CBL showed a higher power conversion efficiency (PCE) of 9.65% based on the PBDT-TS1:PC 71 BM system under the illumination of 100 mW/cm 2 . For the inverted cells based on the PffBT4T-2OD:PC 71 BM system, the PCE can be improved from 4.26% (without CBL) to 9.02% after inserting the Ba(OH) 2 buffer layer. More importantly, the Ba(OH) 2 buffer layer presents similar positive effects in the conventional and inverted all-polymer devices based on a new combination, i.e., the PBDT-TS1:N2200 system. The dramatic enhancement in device performance resulted from the suitable work function of Ba(OH) 2, extremely high transmittance, and excellent film-forming capability. Therefore, inserting Ba(OH) 2 as the CBL is a simple, low-cost, and widely applicable method to simultaneously improve the conventional and inverted photovoltaic device performance.