Printable mesoscopic perovskite solar cells with performance tuning via trifluoroacetamide†

Abstract

Mesoporous TiO₂ (mp-TiO₂), mesoporous ZrO₂ (mp-ZrO₂), and mesoporous carbon (mp-C) without a hole transport layer make up the triple-layer structure of printable mesoscopic perovskite solar cells (p-MPSCs), which have become an extremely promising next-generation photovoltaic technology given their low cost, simplicity of fabrication, and outstanding stability. However, the unique device structure of p-MPSCs requires perovskites to crystallize within a mesoscopic scaffold over ten micrometers thick, resulting in a more complex crystallization process than that in conventional perovskite solar cells, with greater challenges in crystallization control, smaller crystal grains and an increased number of grain boundaries. In this study, trifluoroacetamide (TFAA), containing amide groups, was introduced as an active layer additive to passivate perovskite defects and thus enhanced the performance and stability of p-MPSCs. The CO and –NH₂ groups in TFAA effectively passivate uncoordinated Pb²⁺ and I⁻ ions in the perovskite, enhancing film quality and significantly boosting light absorption. Additionally, TFAA incorporation reduced defect density, improved carrier extraction and transport, and strengthened the built-in electric field, resulting in a PCE of 18.67%. The presence of F⁻ also increased the hydrophobicity of the perovskite film, further improving air stability. Under dark conditions, unencapsulated p-MPSCs with TFAA retained 90% of their initial PCE after 62 days of storage in air (25 ± 5 °C, 40 ± 5% humidity), compared to 76% for untreated p-MPSCs.