Exploring bismuth-based alternatives to lead-halide perovskites

The introduction of lead-halide perovskite materials has opened exciting new directions in the quest for economical thin-film solar cells, reaching high efficiencies over a relatively short period of time. The lead content of these cells, however, poses environmental and commercial concerns, prompting active consideration of lead-free alternatives. Recent theoretical and experimental work with bismuth-based photovoltaic materials, as described in a review featured in APL Materials, could potentially provide the solution.

Bismuth-based compounds are gaining attention because they display little evidence of toxicity, and many of the materials are air-stable. Critically, these materials can replicate the electronic structure of the lead-based perovskites, which is hypothesized to allow them to tolerate defects and achieve high performance.

Recent theoretical and experimental work has identified materials that fulfill this hypothesis (e.g., bismuth oxyiodide), as well as others that replicate the perovskite electronic structure but are not defect-tolerant (e.g., bismuth iodide). Improving our understanding of defect tolerances will help further narrow down the materials with the most potential.

The authors review the wide range of techniques that have been developed to grow bismuth-based compounds. There have been a number of promising leads, such as a vapor-based technique to growth bismuth oxyiodide, which resulted in photovoltaics with quantum efficiencies reaching 80 percent. However, the performance of bismuth-based solar cells lags behind those of lead-based perovskites. Some of the key challenges include achieving thin films without pinholes, and obtaining optimal energy alignment between the electrodes and the semiconductor bands, among others. Overcoming these challenges may realize cheap, efficient photovoltaics that are nontoxic and stable.

Source: “Research Update: Bismuth-based perovskite-inspired photovoltaic materials,” by Lana C. Lee, Tahmida N. Huq, Judith L. MacManus-Driscoll, and Robert L. Z. Hoye, APL Materials (2018). The article can be accessed at https://doi.org/10.1063/1.5029484 .