Improved lead-free solar cells lay groundwork for environmentally friendly designs

Lead-free perovskite solar cells are an emerging design that can replace lead-based cells, which are environmentally impactful. However, such designs suffer from low power conversion efficiencies due to the fast crystallization process that creates uneven surfaces and defects.

Yang et al. created a solution for this problem using additive engineering. Using guanidinium thiocyanate as a functional additive for Cs₂AgBiBr₆-based perovskite solar cells, the researchers were able to enhance the film quality and reduce the defect density.

Previously, such perovskite solar cells have been tested with additional interlayers and low-pressure solution processes to increase the power conversion efficiency. But no investigation about the additive engineering in Cs₂AgBiBr₆-based perovskite solar cells had been reported to enhance the film quality and power conversion efficiencies.

The researchers established an optimal amount of guanidinium thiocyanate could create a power conversion efficiency of 3.02% — much higher than previous efficiency of 2.55% — and retarded the crystallization process and inhibited the formation of bromine vacancies. This allowed the guanidinium thiocyanate to interact with the perovskite precursors to improve the film quality.

The pioneering study lays the groundwork for future environmentally friendly solar cells as researchers strive to close the gap to the theoretical efficiency value of 10.5%.

“This work will provide a new research direction for the design of high-efficiency and stable Cs₂AgBiBr₆-based perovskite solar cells,” said coauthor Wei Wang. “We plan to focus on designing more new and efficient additives to improve the efficiency and stability of Cs₂AgBiBr₆-based perovskite solar cells.”

Source: “First investigation of additive engineering for highly efficient Cs₂AgBiBr₆-based lead-free inorganic perovskite solar cells,” by Xiaoqing Yang, Amin Xie, Huimin Xiang, Wei Wang, Ran Ran, Wei Zhou, and Zongping Shao, Applied Physics Reviews (2021). The article can be accessed at https://doi.org/10.1063/5.0059542 .