Abstract Effect of Ge/(Ge + Sn) composition ratio of Cu2Sn1-xGexS3 (CTGS) films is examined. The CTGS films are fabricated by sulfurization of the 700-nm-thick Cu–SnS2/Ge stacked precursors on Mo-coated soda-lime glass (SLG) substrates. It is revealed that the thickness of Ge precursor (Ge thickness) from 0 to 420 nm enhances the Ge/(Ge + Sn) composition ratio in the CTGS thin films from 0 to about 0.58, thereby increasing bandgap energy (Eg) from approximately 0.97 (Cu2SnS3: CTS) to 1.23 eV (CTGS), respectively. Not only does Ge precursor act as Ge source to form the CTGS films but also it prevents the formation of undesirable MoS2 secondary phase. In addition, the CTGS solar cells with a structure of SLG/Mo/CTGS/CdS/ZnO/ZnO:Al/Ni/Al are fabricated with the Ge thickness from 0 to 420 nm. It is found that the optimized Ge thickness of 200 nm resulting in the Ge/(Ge + Sn) composition ratio of about 0.32 eliminates the excessive MoS2 secondary phase and increases the Eg, thereby increasing conversation efficiency (η) to 5.6% of the CTGS solar cell, higher than that (3.6%) of the CTS solar cell. However, the η is reduced when the Ge thickness over 200 nm because CTGS quality observed by Urbach energy is deteriorated and the conduction band offset at the CdS/CTGS interface demonstrates the large cliff type heterostructure, thus increasing the open-circuit voltage deficit.

中文翻译：

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Cu2Sn1-xGexS3薄膜太阳能电池中Ge/(Ge+Sn)组成比对其物理性能和光伏性能的影响

摘要 研究了 Cu2Sn1-xGexS3 (CTGS) 薄膜的 Ge/(Ge + Sn) 组成比的影响。CTGS 薄膜是通过在镀钼的钠钙玻璃 (SLG) 基板上硫化 700 nm 厚的 Cu-SnS2/Ge 堆叠前体来制造的。结果表明，Ge前体的厚度（Ge厚度）从0到420nm将CTGS薄膜中的Ge/（Ge+Sn）组成比从0提高到约0.58，从而将带隙能量（Eg）从约0.97增加(Cu2SnS3: CTS) 至 1.23 eV (CTGS)。Ge 前驱体不仅作为 Ge 源形成 CTGS 薄膜，而且还可以防止形成不需要的 MoS2 第二相。此外，制备了具有 SLG/Mo/CTGS/CdS/ZnO/ZnO:Al/Ni/Al 结构的 CTGS 太阳能电池，Ge 厚度为 0 至 420 nm。发现优化的 200 nm Ge 厚度导致约 0.32 的 Ge/(Ge + Sn) 组成比消除了过量的 MoS2 二次相并增加了 Eg，从而将转换效率 (η) 提高到 CTGS 的 5.6%太阳能电池，高于 CTS 太阳能电池（3.6%）。然而，当 Ge 厚度超过 200 nm 时，η 会降低，因为 Urbach 能量观察到的 CTGS 质量变差，并且 CdS/CTGS 界面处的导带偏移表现出较大的悬崖型异质结构，从而增加了开路电压赤字。