Multifunctional surface modification of carbon-based all-inorganic CsPbI2Br solar cells by 3-(trifluoromethyl) phenyltrimethyl ammonium iodide

The preparation process of carbon-electrode perovskite solar cells (C-PSCs) without hole transport layers (HTLs) is simple, cost-effective, and the as-prepared C-PSCs exhibit excellent thermal stability. However, there are numerous defects at the interfaces of C-PSCs and grain boundaries. Due to the presence of these defect states, non-radiative recombination of charge carriers occurs, ultimately resulting in significant VOC (voltage open circuit) loss and an energy level mismatch between device structures, which seriously affect the photoelectric conversion efficiency (PCE) and stability of C-PSCs. Therefore, this work uses 3-(trifluoromethyl)-phenyltrimethyl-ammonium iodide (TFPTAI) as a surface modifier to modify the surface of CsPbI2Br. Due to the strong electronegativity of fluorine atoms (F), acting as electron-withdrawing groups, they promote the separation of positive and negative charge centers in the molecule. This, in turn, can effectively induce strong binding of ammonium cations (NH+) with negatively charged defects, consequently suppressing the non-radiative recombination of charge carriers. In addition, thanks to the ordered arrangement of F atoms, a hydrophobic protective umbrella is constructed on the perovskite surface layer, effectively improving the stability of the device. The highest PCE of the as-prepared device is 14.02%, surpassing the optimal PCE of the original device at 12.46%. Simultaneously, the surface-modified device exhibits excellent environmental stability.