Multifunctional ionic liquid boosts the efficiency of hole transport layer-free carbon-based perovskite solar cells beyond 20%

Abstract

The planar triple-layer hole transport layer (HTL)-free carbon-based perovskite solar cells have the advantages of low cost and high stability, but their low efficiency hinders the commercialization process. Here, a dual regulation strategy for bulk defects and interface defects has been developed. After selecting dimethylamine (DMA) as the fixed cation and selecting the anion site (I⁻, Br⁻, Cl⁻, HCOO⁻), an ionic liquid additive, DMAFo, was synthesized, achieving multiple functions such as energy level regulation, removal of residual PbI₂ at the buried interface, retarding crystallization through the intermediate phase DMAPbI_(3−x)HCOO_x, filling halide vacancy defects, and releasing residual stress. This effectively reduces energy loss during carrier transport and obtains higher-quality perovskite films. Under the synergistic effect of DMA⁺ and HCOO⁻, both bulk defects and interface defects in the perovskite film were simultaneously addressed. The device prepared using DMAFo as an additive achieved the best device efficiency of 20.77%, and after continuous maximum power point tracking for 1200 h, the device efficiency remained almost unchanged, demonstrating excellent operational stability.