Polyamino acid interlayer facilitates electron extraction in narrow band gap fullerene-free organic solar cells with an outstanding short-circuit current

Benefitted from n-doping induced by the α-PLL charge extraction layer and resultant interfacial modifications, ultra-narrow bandgap fullerene-free solar cells based on PTB7-Th:IEICO-4F blends receive an enhancement on the short-circuit current (= 26.6 mA/cm2) and ultimate power conversion efficiency exceeding 12%, which is among the highest performance for devices with similar bandgaps.189