Suppressing charge carrier recombination in halide perovskite solar cells by ferroelectric polarization

Abstract

Cesium-based perovskite solar cells (PSCs) are favorable alternatives to address the photovoltaic performance issues of organic–inorganic halide perovskites. Here, adding cesium to the perovskite composition is explored to enhance the morphology and crystallization of the perovskite layers. Cells prepared with optimized 10 wt% CsI demonstrate improvement in the power conversion efficiency (PCE) from 14.4 to 18.1% due to better light absorption. We show that the association of the ferroelectric polyvinylidene difluoride (PVDF) polymer in PSCs leads to localized improvements of the electric field, which subsequently leads to more efficient charge carrier extraction and transfer. Spontaneous electric polarization increases the desired separation of photo-generated charge carriers and allows them to achieve voltages higher than conventional PSCs. By optimizing PVDF concentrations in the perovskite active layer, the PSCs exhibit an improved efficiency of 19.7%. Furthermore, applying external bias results in achieving the highest PCE of 21.7%. Higher efficiency originates from ferroelectric dipoles rather than any morphological modification. Dipole-aligned PVDF provides higher charge carrier recombination resistance and more balanced charge carrier mobility which leads to the suppression of hysteresis. PSCs fabricated with Cs/PVDF retain 83% of their initial PCE.