Kesterite Cu₂ZnSn(S,Se)₄ solar cells fabricated from DMSO molecular solutions exhibit very different open circuit voltage (V_oc) when the tin precursor has a different oxidation state (Sn²⁺ vs. Sn⁴⁺). Here, the grain growth mechanism of the two absorbers was used as a platform to investigate the large voltage deficit issue that limits kesterite solar cell efficiency. The secondary sulfide composed Sn²⁺ precursor film took a multi-step phase fusion reaction path with secondary SnSe₂ existing on the film surface during the whole grain growth, which forms in a very defective surface whereas a uniform kesterite structured Sn⁴⁺ precursor film took a direct transformation reaction path along with a top down and bottom up bi-direction grain growth that forms a uniform and less defective surface. Characterizations show that both absorber films exhibit similar bulk electronic properties with comparable band and potential fluctuations, Cu–Zn disorder level and tail states, and the much lower V_oc of the Sn²⁺ device than the Sn⁴⁺ device primarily comes from the serious recombination near the junction as revealed by the large ideality factor and reverse saturation current. Our results demonstrate that the large V_oc deficit of the kesterite solar cell mainly comes from surface deep defects that originated from the multi-phase fusion grain growth mechanism. The high efficiency (>12%) and low V_oc deficit (<300 mV) of Sn⁴⁺ processed CZTSSe solar cells highlight that direct phase transformation grain growth is a new strategy to fabricate high quality kesterite absorbers, which can also be applied to other multi-element thin film semiconducting materials.

中文翻译：

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从DMSO溶液中Sn2 +和Sn4 +前驱体诱导的两种晶粒生长机理中，识别钾长石太阳能电池的Voc缺乏的根源

当锡前体具有不同的氧化态（Sn ²⁺与Sn ⁴⁺）时，由DMSO分子溶液制成的Kesterite Cu ₂ ZnSn（S，Se）₄太阳能电池表现出截然不同的开路电压（V _oc）。在这里，两种吸收剂的晶粒长大机理被用作研究限制硅藻土太阳能电池效率的大电压不足问题的平台。次级硫化物组成的Sn ²⁺前驱体膜经历了多步的相融合反应路径，在整个晶粒生长过程中，次级SnSe ₂存在于膜表面，形成了非常缺陷的表面，而均匀的钾长石结构的Sn ⁴⁺前体薄膜采用了直接转化反应路径，并形成了上下均匀的缺陷较少的自上而下和自下而上的双向晶粒生长。表征表明，两种吸收膜都具有相似的体电子性质，具有可比的能带和势能波动，Cu-Zn无序能级和尾态，并且Sn ²⁺器件的V _oc低于Sn ⁴⁺器件的V _oc主要来自于严重的大理想因子和反向饱和电流显示出结附近的重组。我们的结果表明，较大的V _ocKesterite太阳能电池的缺陷主要来自表面深缺陷，该缺陷是由多相熔合晶粒生长机制引起的。Sn ⁴⁺处理的CZTSSe太阳能电池的高效率（> 12％）和低V _oc缺陷（<300 mV）突出表明，直接相变晶粒长大是制造高质量Kesterite吸收剂的新策略，也可应用于其他多元素薄膜半导体材料。