Rational molecular doping to enhance interfacial carrier dynamics for reliable hole transport layer-free perovskite solar cells†

Abstract

Charge selective contacts are critical in perovskite solar cells (PSCs) for charge dissociation, collection and transport. However, these layers can cause interfacial incompatibility and complicate the manufacturing process. To address these challenges, simplifying the PSC structure has become a key strategy. Although efforts have been made to develop hole transport layer (HTL)-free inverted PSCs, their photovoltaic performance has not yet matched that of conventional PSCs, and the mechanisms of interfacial charge dynamics in these simplified devices remain poorly understood. In this work, we propose a powerful strategy of rational molecular doping to optimize the interfacial energy-level alignment and carrier dynamics in PSCs. We demonstrate that the electron affinity of p-type organic molecules is pivotal in controlling perovskite crystallization and improving the quality of perovskite films, which in turn enhances interfacial charge collection and reduces carrier recombination losses. By doping with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), we significantly enhance the conductivity of perovskite films and strengthen the electronic contact with the conductive substrate. As a result, F4TCNQ-based HTL-free inverted PSCs achieve an impressive power conversion efficiency of 18.07%, surpassing the 9.75% of control devices. This study introduces an effective method for fabricating reliable HTL-free PSCs through rational molecular doping, laying the groundwork for further improvements in device performance.