Platzer Björkman Charlotte, Larsen Jes K, Saini Nishant, Babucci Melike, Martin Natalia
Div. Solar Cell Technology, Dep. Materials Science and Engineering, Uppsala University, Sweden.
Faraday Discuss. 2022 Oct 28;239(0):38-50. doi: 10.1039/d2fd00052k.
Kesterite CuZnSnS (CZTS), used for thin film solar cells, has a band gap energy around 1.5-1.6 eV with possibilities for further increase through alloying. In some applications for wide band gap solar cells, reduced absorber thickness can be beneficial, to allow partial light transmission. Reduced thickness can also be beneficial to reduce bulk recombination, and so called ultrathin solar cells (<700 nm thick) have been studied for several materials systems. Here, we report performance for CZTS devices down to 250 nm thickness and show that performance loss from thickness reduction is relatively small, partly due to short minority carrier diffusion length. Insertion of thin passivation layers (AlO, SiO or HfO) at the Mo/CZTS interface gives improved performance of ultrathin devices, from 4.7% to 5.6% efficiency for best performing cells having 250 nm thick CZTS with Mo as compared to Mo/AlO back contact. The approach of NaF post deposition for making isolating passivation layers conductive is tested for the first time for CZTS and is shown to work. For fabrication of CZTS devices on transparent ITO back contact, the insertion of passivation layers can reduce diffusion of indium into CZTS, but device performance is lower than on Mo back contacts.
用于薄膜太阳能电池的硫铜锌锡（CZTS），其带隙能量约为1.5 - 1.6电子伏特，通过合金化有可能进一步提高。在一些宽带隙太阳能电池的应用中，减小吸收层厚度可能是有益的，以允许部分光透射。减小厚度也有利于减少体复合，并且已经针对几种材料系统研究了所谓的超薄太阳能电池（厚度小于700纳米）。在此，我们报告了厚度低至250纳米的CZTS器件的性能，并表明厚度减小导致的性能损失相对较小，部分原因是少数载流子扩散长度较短。在Mo/CZTS界面插入薄的钝化层（AlO、SiO或HfO）可提高超薄器件的性能，与Mo/AlO背接触相比，对于具有250纳米厚CZTS且以Mo为背接触的最佳性能电池，效率从4.7%提高到了5.6%。首次对CZTS测试了用于使隔离钝化层导电的NaF后沉积方法，结果表明该方法可行。对于在透明ITO背接触上制造CZTS器件，插入钝化层可减少铟向CZTS中的扩散，但器件性能低于在Mo背接触上的性能。
