Exceeding 20% Efficiency for Highly Efficient and Stable Inverted Perovskite Solar Cells via Sodium Borohydride Induced Interface Engineering

Poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) is widely used as a hole transport layer in inverted perovskite solar cells (PSCs). However, due to the serious interface defects, imperfect energy level arrangement, and low hole transfer rate between PEDOT:PSS and perovskite, the realization of efficient and stable inverted PSCs is hindered. Herein, ionic salt sodium borohydride is used as an interfacial modifier between PEDOT:PSS and MAPbI(3-x)Cl(x). NaBH4 acts as an anchor to bond Pb2+ to the PEDOT:PSS surface and guides the growth of the perovskite. The champion power conversion efficiency (PCE) of the device based on NaBH4-PEDOT:PSS reaches 20.21%, which is improved by 27.5% compared with the device based on PEDOT:PSS (15.84%). This PCE is one of the highest in inverted PSCs with PEDOT:PSS as the hole transport layer and MAPbI(3-x)Cl(x) as the active layer. The improved device performance is mainly attributed to the reduced valence band edge of PEDOT:PSS which matches better with the HOMO of MAPbI(3-x)Cl(x), and the hole transfer rate is increased from 2.65 x 10(10) to 3.69 x 10(10) s(-1). The long-term stability of the optimized device exceeds 1000 h. This work provides a simple and effective strategy to improve the PCE and stability of inverted PSCs, which is a benefit for future popularization.