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ABSTRACT: The mixed halide perovskites have emerged as efficient light absorbers to construct perovskite solar cells which continually break the power conversion efficiency (PCE) records recently. Upon element substitution, it reveals inhomogeneity in polycrystalline films due to composition separation, which leads to local lattice mismatches and thus emergent residual strains. Thus far, understanding the nature of these residual strains and their effects on photovoltaic device performance, is still absent. Herein we study the evolution of residual strain over the mixed perovskite films by using the depth-dependent grazing incident X-ray diffraction measurement. We identify the gradient distribution of in-plane strain component perpendicular to the substrate. We reveal its impacts on the carrier dynamics over corresponding devices, which is stemmed from the strain gradient induced energy bands bending of perovskite absorber as indicated by first-principles calculations. We further develop a feasible method to modulate the tensile or compressive nature and gradient distribution of residual strains in a controllable manner, which leads to enhanced PCEs up to 20.7% (certified) in devices via rational strain engineering. Moreover, we investigate the effects of strain on materials stability. It demonstrates the residual strains as a powerful toolbox to tailor the optoelectronic properties of hybrid halide perovskite materials, which further promotes device performance for not only perovskite solar cells but also quantum dot/organic solar cells.


BIOGRAPHY: Qi Chen received both his B.S. and M.S. degrees from Tsinghua University, and received his Ph.D. degree from the University of California, Los Angeles (UCLA). From 2013 to 2016, he worked as a postdoc fellow at the California Nanosystem Institute (CNSI), UCLA, under Prof. Yang Yang's supervision. In the year 2016, he joined the Beijing Institute of Technology (BIT). His research focuses on hybrid materials design, processing and applications in opto-electronics and for energy harvesting and storage. He is now working on the commercialization of perovskite photovoltaics. To date, he has published over 100 papers on highly impact journals such as Science, Nature Communications, Joule, Advanced Materails, Journal of American Chemical Society. These work has recieved wide attention over the research commuity with the total citation over 18000.

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