Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC, 27708, USA.
Department of Chemistry, Duke University, Durham, NC, 27708, USA.
Adv Mater. 2017 Jun;29(24). doi: 10.1002/adma.201606945. Epub 2017 Apr 20.
In recent years, Cu ZnSn(S,Se) (CZTSSe) materials have enabled important progress in associated thin-film photovoltaic (PV) technology, while avoiding scarce and/or toxic metals; however, cationic disorder and associated band tailing fundamentally limit device performance. Cu BaSnS (CBTS) has recently been proposed as a prospective alternative large bandgap (~2 eV), environmentally friendly PV material, with ~2% power conversion efficiency (PCE) already demonstrated in corresponding devices. In this study, a two-step process (i.e., precursor sputter deposition followed by successive sulfurization/selenization) yields high-quality nominally pinhole-free films with large (>1 µm) grains of selenium-incorporated (x = 3) Cu BaSnS Se (CBTSSe) for high-efficiency PV devices. By incorporating Se in the sulfide film, absorber layers with 1.55 eV bandgap, ideal for single-junction PV, have been achieved within the CBTSSe trigonal structural family. The abrupt transition in quantum efficiency data for wavelengths above the absorption edge, coupled with a strong sharp photoluminescence feature, confirms the relative absence of band tailing in CBTSSe compared to CZTSSe. For the first time, by combining bandgap tuning with an air-annealing step, a CBTSSe-based PV device with 5.2% PCE (total area 0.425 cm ) is reported, >2.5× better than the previous champion pure sulfide device. These results suggest substantial promise for the emerging Se-rich Cu BaSnS Se family for high-efficiency and earth-abundant PV.
近年来，Cu ZnSn(S,Se)（CZTSSe）材料在相关的薄膜光伏（PV）技术中取得了重要进展，同时避免了稀缺和/或有毒金属的使用；然而，阳离子无序和相关的能带尾态从根本上限制了器件性能。Cu BaSnS（CBTS）最近被提议作为一种有前途的替代大带隙（~2eV）、环保的光伏材料，其相应器件已展示出约 2%的功率转换效率（PCE）。在这项研究中，采用两步工艺（即前驱体溅射沉积后进行连续的硫化/硒化），制备出高质量、名义上无针孔的、具有大（>1μm）硒掺杂（x=3）Cu BaSnS Se（CBTSSe）晶粒的薄膜，适用于高效光伏器件。通过在硫化物薄膜中掺入硒，可以在 CBTSSe 三方结构家族中实现具有 1.55eV 带隙的吸收体层，非常适合单结 PV。量子效率数据在吸收边缘以上波长的急剧转变，加上强烈的尖锐光致发光特征，证实了 CBTSSe 中能带尾态的相对缺失，与 CZTSSe 相比。首次通过结合带隙调谐与空气退火步骤，报道了基于 CBTSSe 的光伏器件，其 PCE 为 5.2%（总面积为 0.425cm ），比之前的纯硫化物器件冠军高出 2.5 倍以上。这些结果表明，富 Se 的 Cu BaSnS Se 族在高效和地球丰富的 PV 中有很大的应用潜力。
