π-Conjugated small molecules enable efficient perovskite growth and charge-extraction for high-performance photovoltaic devices

A pi-conjugated small molecule N,N'-bis(naphthalen-l-yl)-N,N'+-bis(phenyl)benzidine (NPB) is introduced into a poly (bis(4-phenyl)(2,4,6-trimethylphenyl)amine) (PTAA) hole transport layer in inverted perovskite solar cells (PSCs). The NPB doping induces better perovskite crystal growth owing to a strong pi-pi interaction with PTAA and cation-pi interactions with CH3NH3+ (MA(+)). In addition, NPB doping not only improves the wettability of PTAA and regulates the perovskite crystallization to achieve a larger grain size, but also moves the valence band energy of the hole transport layer closer to the perovskite layer. Consequently, the fabricated PSCs delivered a power conversion efficiency (PCE) of 20.15%, with a short-circuit current density (J(SC)) of 22.60 mA/cm(2) and open-circuit voltage (V-OC) of 1.14 V. This outcome indicates that PTAA:NPB composite materials present great potential for fabricating high-performance PSCs.