Ghosh Biplab, Wu Bo, Mulmudi Hemant Kumar, Guet Claude, Weber Klaus, Sum Tze Chien, Mhaisalkar Subodh, Mathews Nripan
Energy Research Institute @ Nanyang Technological University (ERI@N) , 637553 , Singapore.
Interdisciplinary Graduate School , Nanyang Technological University , 639798 , Singapore.
ACS Appl Mater Interfaces. 2018 Oct 17;10(41):35000-35007. doi: 10.1021/acsami.7b14735. Epub 2018 Oct 8.
Lead (Pb) halide perovskites have attracted tremendous attention in recent years because of their rich optoelectronic properties, which have resulted in more than 22% power conversion efficient photovoltaics (PVs). Nevertheless, Pb-metal toxicity remains a huge hurdle for extensive applications of these compounds. Thus, alternative compounds with similar optoelectronic properties need to be developed. Bismuth possesses electronic structure similar to that of lead with the presence of ns electrons that exhibit rich structural variety as well as interesting optical and electronic properties. Herein, we critically assess CsBiI as a candidate for thin-film solar cell absorber. Despite a reasonable optical band gap (∼2 eV) and absorption coefficient, the power conversion efficiency of the CsBiI mesoscopic solar cells was found to be severely lacking, limited by the poor photocurrent density. The efficiency of the CsBiI solar cell can be slightly improved by changing the stoichiometry of the precursor solutions, which is most probably due to the reduction in nonradiative defects as evident from our single-crystal photoluminescence spectroscopy. However, detailed investigations on pristine CsBiI reveal that zero-dimensional molecular crystal structure remains one of the main bottlenecks in achieving high performance. On the basis of our comprehensive studies, we have proposed that a continuous network of three-dimensional crystal structure should be another major criterion in addition to proper band gap and suitable optical properties of the future PV compounds.
近年来，卤化铅（Pb）钙钛矿因其丰富的光电特性而备受关注，这些特性使得光伏发电（PV）的功率转换效率超过了22%。然而，铅金属的毒性仍然是这些化合物广泛应用的巨大障碍。因此，需要开发具有类似光电特性的替代化合物。铋具有与铅相似的电子结构，存在ns电子，表现出丰富的结构多样性以及有趣的光学和电子特性。在此，我们严格评估CsBiI作为薄膜太阳能电池吸收体的候选材料。尽管CsBiI具有合理的光学带隙（约2 eV）和吸收系数，但发现CsBiI介观太阳能电池的功率转换效率严重不足，受光电流密度低的限制。通过改变前驱体溶液的化学计量比，CsBiI太阳能电池的效率可以略有提高，这很可能是由于非辐射缺陷的减少，这从我们的单晶光致发光光谱中可以明显看出。然而，对原始CsBiI的详细研究表明，零维分子晶体结构仍然是实现高性能的主要瓶颈之一。基于我们的综合研究，我们提出，除了未来光伏化合物具有合适的带隙和适宜的光学特性外，三维晶体结构的连续网络应该是另一个主要标准。
