Surface planarization enabled low-dimensional perovskite-leveling compound for carbon-based CsPbI2Br perovskite solar cells

The carbon-based, hole-transporting layer-free all-inorganic CsPbI₂Br perovskite solar cells (HTL-free C-PSCs) offer significant promise for photovoltaic applications due to their cost-effectiveness and remarkable stability. However, the substantial undercoordinated Pb²⁺ and halogen vacancies at the carbon electrode/perovskite interface seriously hamper their performance. Herein, 4-fluorobenzylamine trifluoroacetate (p-F-PMATFA) was introduced to reacted directly with the perovskite layer's surface, yielding a low-dimensional compound that effectively levels the carbon/perovskite interface. This strategy improves the quality of the perovskite film, resulting in uniform and dense film topography, diminished trap density, and mitigated charge recombination and ion migration. Furthermore, the formation of highly planar interfaces and the passivation of interfacial defects facilitates efficient hole extraction at the carbon/perovskite junction. As a result, the champion device exhibits a high power conversion efficiency (PCE) of 13.41 %. Notably, the unencapsulated treated device maintains over 95 % of its initial PCE after being stored in a nitrogen atmosphere at 85 °C for 500 h. Our work present a straightforward yet highly effective strategy for developing cost-effective, efficient, and stable HTL-free C-PSCs, offering a promising avenue for future photovoltaic technologies.