Bifunctional bridging capping layer enables 24.5% efficiency of perovskite solar cells with polymer-based hole transport materials

Abstract

Developing a bridge capping layer between perovskite and hole transport layer materials (HTMs) in the n-i-p perovskite solar cells (pero-SCs) is an effective approach to modify the morphology of HTMs and passivate the perovskite simultaneously. Herein, we select the quinoxaline-based bifunctional passivation agent, quinoxalin-6-yl-methylamine hydrochloride (QxMACl), as the bridging layer, and a D-A copolymer PBQ12 containing the same quinoxaline unit as an HTM for the n-i-p pero-SCs. Due to the π-π stacking among the common quinoxaline units in the bridge layer and HTM, QxMACl induces the π-π stacking of the PBQ12 film and improves the film morphology of HTMs with better conductivity. Additionally, QxMACl can effectively passivate the perovskite surface, and PBQ12 possesses appropriate energy levels and high hole mobility. The pero-SCs based on FAPbI₃ with PBQ12/QxMACl treatment showed a higher power conversion efficiency (PCE) of 24.05% and outstanding stability, maintaining 95.4% and 92.1% of its initial PCE after 750 h of storage and after over 800 h of thermal annealing at 85 °C, respectively. To further enhance the PCE of the PBQ12/QxMACl-based devices, we developed a non-metal ion dopant for the PBQ12 HTM. Through trace doping of PBQ12 HTM by the non-metal ion dopant, the PCE of the PBQ12/QxMACl-based devices reached 25.24% (the calibrated PCE of 24.55% by the National Institute of Metrology, China).