Tailoring Perovskite Surface Potential and Chelation Advances Efficient Solar Cells

Abstract

Modifying perovskite surface using various organic ammonium halide cations has proven to be an effective approach for enhancing the overall performance of perovskite solar cells. Nevertheless, the impact of the structural symmetry of these ammonium halide cations on perovskite interface termination has remained uncertain. Here, we investigate the influence of symmetry on the performance of the devices, using molecules based on symmetrical bis(2‐chloroethyl)ammonium cation (B(CE)A⁺) and asymmetrical 2‐chloroethylammonium cation (CEA⁺) as interface layers between the perovskite and hole transport layer. Our results reveal that the symmetrical B(CE)A⁺ cations lead to a more homogeneous surface potential and more comprehensive chelation with uncoordinated Pb²⁺ compared to the asymmetrical cations, resulting in a more favorable energy band alignment and strengthened defect healing. This strategy, leveraging the spatial geometrical symmetry of the interface molecules, promotes hole carrier extraction between functional layers and reduces nonradiative recombination on the perovskite surface. Consequently, perovskite solar cells processed with the symmetrical B(CE)A⁺ cation achieve a power conversion efficiency (PCE) of 25.60% and retain approximately 91% of their initial PCE after 500 hours of maximum power point operation. This work highlights the significant benefits of utilizing structurally symmetrical cations in promoting the performance and stability of perovskite solar cells.

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