Tailoring Thick Film Crystallization and Facet Orientation via Potassium Acetate for Efficient Bifacial Perovskite Solar Cells
Xianggang Chen, Miao Yang, Xiaoxu Sun, Xing Li, Yuhang Xie, Xuzheng Feng, Jixiang Tang, Longfei Yan, Shuyuan Fan, Songyuan Dai, Wenzhong Shen, Molang Cai
Abstract
Bifacial perovskite solar cells (PSCs) require micron-thick perovskite layers to compensate for optical loss from transparent electrodes, but high defect densities limit efficiency. Here, we introduce a potassium acetate (KAc) post-treatment on microthick PbI 2 films to form an amorphous KAc-PbI 2 intermediate, which facilitates ammonium salt incorporation and promotes perovskite crystallization. During the second step, released Ac – and K + ions selectively adsorb onto (111) and (001) facets, respectively, directing vertical crystal growth with (001) orientation. This strategy reduces defect density and improves film quality in thick perovskite layers. As a result, the bifacial PSC achieves a power conversion efficiency (PCE) of 21.33%, bifaciality exceeding 80%, and a record power generation density (PGD) of 24.72 mW cm –2 under 0.2 albedo, representing the highest reported PGD for n-i-p bifacial PSCs. After 500 h of continuous illumination at the maximum power point, the KAc-treated bifacial device retained its initial PCE.