The conversion efficiency of kesterite solar cells has been stagnated at 12.6% since 2013. In contrast to chalcopyrite solar cells, the performance of kesterite solar cells is seriously limited by heterojunction interface recombination. Here we demonstrate kesterite/CdS heterojunction is constructed on a Zn-poor surface due to the dissolution of Zn²⁺ during chemical bath deposition. The occupation of Cd²⁺ on the Zn site and re-deposition of Zn²⁺ into CdS creates a defective and lattice-mismatched interface. Low-temperature annealing of the kesterite/CdS junction drives migration of Cd²⁺ from absorber back to CdS and Zn²⁺ from absorber bulk to surface, achieving a gradient composition and reconstructing an epitaxial interface. This greatly reduces interface recombination and improves device open-circuit voltage and fill factor. We achieve certified 12.96% efficiency small-area (0.11 cm²) and certified 11.7% efficiency large-area (1.1 cm²) kesterite devices. The findings are expected to advance the development of kesterite solar cells.

钾长石太阳能电池的转换效率自 2013 年以来一直停滞在 12.6%。与黄铜矿太阳能电池相比，钾长石太阳能电池的性能受到异质结界面复合的严重限制。在这里，我们展示了由于化学浴沉积过程中 Zn ^{2+的溶解，在贫锌表面上构建了 kesterite/CdS 异质结。Cd 2+}在 Zn 位点上的占据和 Zn ²⁺重新沉积到 CdS 中会产生缺陷和晶格不匹配的界面。锡铅矿/CdS 结的低温退火驱动 Cd ²⁺从吸收体迁移回 CdS 和 Zn ²⁺从吸收体到表面，实现梯度组合并重建外延界面。这大大减少了界面复合并提高了器件开路电压和填充因子。我们实现了经认证的效率为 12.96% 的小面积 (0.11 cm ² ) 和经认证的效率为 11.7% 的大面积 (1.1 cm ² ) 锡铅矿设备。预计这些发现将推动钾长石太阳能电池的发展。