Ex situ Ge-doping of CZTS nanocrystals and CZTSSe solar absorber films.
Ex situ Ge-doping of CZTS nanocrystals and CZTSSe solar absorber films.
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DOI：
10.1039/d2fd00069e
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发表时间：
2022-07
影响因子：
3.4
通讯作者：
Matthew C Naylor;D. Tiwari;Alice Sheppard;J. Laverock;Stephen Campbell;Bethan Ford;Xinya Xu;Michael D K Jones;Y. Qu;P. Maiello;V. Barrioz;N. Beattie;N. Fox;D. Fermín;G. Zoppi
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文献类型：
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作者：
Matthew C Naylor;D. Tiwari;Alice Sheppard;J. Laverock;Stephen Campbell;Bethan Ford;Xinya Xu;Michael D K Jones;Y. Qu;P. Maiello;V. Barrioz;N. Beattie;N. Fox;D. Fermín;G. Zoppi
Cu_2ZnSn（S，Se）_4（CZTSSe）是一种很有前途的薄膜光电转换材料，但CZTSSe的开路电压（VOC）不足使其转换效率不能超过13%。CZTSSe是一种高度补偿的材料，其富含点缺陷并且易于形成第二相。这些缺陷的景观是复杂的，一些缓解是可能的，通过采用非化学计量的条件。用于减少不期望的缺陷的影响的另一种途径是材料的掺杂和合金化以抑制某些缺陷并改善结晶，例如用锗。大多数工作是在富含硒的气氛中退火之前，将Ge存款在通过物理气相沉积沉积的堆叠的金属前体附近。在这里，我们使用一个既定的热注入过程中合成Cu 2 ZnSnS 4纳米晶体的预定组合物，随后掺杂锗硒化过程中，以帮助重结晶和减少锡物种的影响。通过Ge掺入，我们展示了结构变化，能带隙的变化可以忽略不计，但结晶度和晶粒形态的大幅增加，这与Ge-Se生长机制有关，并且VOC和转换效率都有所提高。我们使用表面能量过滤的光电子发射显微镜（EF-PEEM）映射的表面功函数地形，并显示出改进的电子景观，我们归因于减少低局部有效功函数（LEWF）锡（II）硫族化物相的偏析。
Cu2ZnSn(S,Se)4 (CZTSSe) is a promising material for thin-film photovoltaics, however, the open-circuit voltage (VOC) deficit of CZTSSe prevents the device performance from exceeding 13% conversion efficiency. CZTSSe is a heavily compensated material that is rich in point defects and prone to the formation of secondary phases. The landscape of these defects is complex and some mitigation is possible by employing non-stoichiometric conditions. Another route used to reduce the effects of undesirable defects is the doping and alloying of the material to suppress certain defects and improve crystallization, such as with germanium. The majority of works deposit Ge adjacent to a stacked metallic precursor deposited by physical vapour deposition before annealing in a selenium rich atmosphere. Here, we use an established hot-injection process to synthesise Cu2ZnSnS4 nanocrystals of a pre-determined composition, which are subsequently doped with Ge during selenisation to aid recrystallisation and reduce the effects of Sn species. Through Ge incorporation, we demonstrate structural changes with a negligible change in the energy bandgap but substantial increases in the crystallinity and grain morphology, which are associated with a Ge-Se growth mechanism, and gains in both the VOC and conversion efficiency. We use surface energy-filtered photoelectron emission microscopy (EF-PEEM) to map the surface work function terrains and show an improved electronic landscape, which we attribute to a reduction in the segregation of low local effective work function (LEWF) Sn(II) chalcogenide phases.