Nonconjugated Polymer Poly(vinylpyrrolidone) as an Efficient Interlayer Promoting Electron Transport for Perovskite Solar Cells

The interfaces between perovskite layer and electrodes play a crucial role on efficient charge transport and extraction in perovskite solar cells (PSCs). Herein, for the first time we applied a low-cost nonconjugated polymer poly(vinylpyrrolidone) (PVP) as a new interlayer between PCBM electron transport layer (ETL) and Ag cathode for high-performance inverted planar heterojunction perovskite solar cells (iPSCs), leading to a dramatic efficiency enhancement. The CH₃NH₃PbI_3-xCl_x-based iPSC device incorporating the PVP interlayer exhibited a power conversion efficiency (PCE) of 12.55%, which is enhanced by ∼15.9% relative to that of the control device without PVP interlayer (10.83%). The mechanistic investigations based on morphological, optical, and impedance spectroscopic characterizations reveal that incorporation of PVP interlayer promotes electron transport across the CH₃NH₃PbI_3-xCl_x perovskite/Ag interface via PCBM ETL. Besides, PVP incorporation induces the formation of a dipole layer, which may enhance the built-in potential across the device, conjunctly promoting electron transport from PCBM to Ag cathode and consequently leading to significantly improved fill factor (FF) from 58.98 to 66.13%.