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Hybrid perovskites are spectacularly efficient materials for photovoltaics. Just a few years after the first solar cells were fabricated, they have already achieved solar conversion efficiencies greater than 22 percent. Interestingly, the fundamental mechanisms that are responsible for this high efficiency are still being vigorously debated.
A thorough understanding of these mechanisms is essential to enable further improvements, and computational studies conducted using the National Energy Research Scientific Computing Center (NERSC) at Lawrence Berkeley National Laboratory have produced critical new insights. Chris Van de Walle's group at the University of California, Santa Barbara (UCSB) has reported these breakthroughs in two recent papers: X. Zhang, J.-X. Shen, W. Wang, and C. G. Van de Walle, ACS Energy Lett. 3, 2329 (2018) and J.-X. Shen, X. Zhang, S. Das, E. Kioupakis, and C. G. Van de Walle, Adv. Energy Mater. 8, 1801027 (2018).
Perovskites - Group - Materials - Molecules - Framework
Hybrid perovskites are a group of materials that combine organic molecules with an inorganic framework in a perovskite lattice structure. A number of research groups previously attributed the high efficiency of the hybrid perovskites to an indirect band gap originating from strong spin-orbit coupling. It was argued that the indirect nature of the gap suppresses radiative recombination between electrons and holes and thus minimizes undesirable carrier recombination. UCSB postdoc Xie Zhang and Ph.D. student Jimmy-Xuan Shen (who has since graduated) demonstrated that this was incorrect by developing a cutting-edge, first-principles approach to accurately determine the spin texture of the band edges and quantitatively compute the radiative recombination rates. For methylammonium lead iodide (the prototype hybrid perovskite commonly referred to as MAPI) they found that the radiative recombination is actually as strong as...
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