One of the primary challenges impeding an improvement in the efficiency of kesterite (CZTSSe) solar cells is the significant open-circuit voltage deficit (V_oc,def), which is mainly due to high defect concentrations and energy level mismatches at the heterojunction interface. Here, we propose a novel low-temperature surface modification strategy by the in situ incorporation of n-type Ag₂S at the front interface of CZTSSe. We first found that the formation of narrow-bandgap Ag₂S induces secondary diffusion of microregion elements on the CZTSSe absorber surface. During annealing, Sn- and Zn-doped Ag₂S forms and serves three critical functions in CZTSSe devices: boosting of p–n conversion, front-interface bandgap grading, and defect passivation. These processes collectively reduce the carrier transport barrier and enhance charge extraction capability. Additionally, the outward diffusion of Ag⁺ to the absorber surface partially substitutes Cu⁺, reducing concentrations of Cu_Zn, Cu_Sn, and [2Cu_Zn + Sn_Zn] defects, thereby suppressing non-radiative recombination. Notably, the efficiency of an Ag₂S-modified CZTSSe device increases from 12.38% to 14.25%, achieving the highest V_oc to date at 0.584 V and the lowest V_oc,def of only 0.228 V. This novel strategy offers new insights for significantly promoting V_oc in p-type copper-based thin-film solar cells.

中文翻译：

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具有最低 Voc，def 的 N 型 Ag2S 改性 CZTSSe 太阳能电池


阻碍钙钛矿 （CZTSSe） 太阳能电池效率提高的主要挑战之一是显着的开路电压赤字 （V_oc，def），这主要是由于异质结界面处的高缺陷浓度和能级不匹配。在这里，我们提出了一种新的低温表面改性策略，通过在 CZTSSe 的正面界面原位掺入 n 型 Ag₂S。我们首先发现窄带隙 Ag₂S 的形成诱导了 CZTSSe 吸收器表面微区域元素的二次扩散。在退火过程中，Sn 和 Zn 掺杂的 Ag₂S 形成并在 CZTSSe 器件中发挥三个关键功能：促进 p-n 转换、前界面带隙分级和缺陷钝化。这些过程共同减少了载流子传输障碍并增强了电荷提取能力。此外，Ag⁺ 向外扩散到吸收体表面部分取代了 Cu⁺，降低了 Cu_Zn、Cu_Sn 和 [2Cu_Zn + Sn_Zn] 缺陷的浓度，从而抑制了非辐射复合。值得注意的是，Ag₂S 改性 CZTSSe 器件的效率从 12.38% 提高到 14.25%，实现了迄今为止最高的 V oc 为 0.584 V，最低的 V_oc，def 仅为 0.228 V。这种新颖的策略为显著促进 p 型铜基薄膜太阳能电池中的 V_oc 提供了新的见解。