2, The University of Toledo, Toledo, Ohio, United States
3, Tokyo Institute of Technology, Yokohama, , Japan
To enable the ultimate commercialization of emerging Pb halide perovskite (ABX3) solar cell technology, extensive efforts have been undertaken to overcome their toxicity and air-instability issues, by identifying analogous nontoxic or low-toxicity and air-stable halide perovskite-based absorbers. Substituting Pb by a combination of monovalent and trivalent cations to form A2B(I)B(III)X6 halide double perovskites has been considered as an attractive approach for achieving this goal. So far, theoretical studies have predicted many halide double perovskites as promising absorbers, primarily because of their suitable optoelectronic properties. Some halide double perovskites have been synthesized, but have not produced efficient solar cells. Besides optoelectronic properties, defect properties of the absorbers must be appropriate also for producing efficient solar cells. A promising absorber must exhibit a suitable semiconductivity with sufficiently low majority carrier density of e.g. <1017 cm−3 and have a low density of deep level defects since both the free carriers and the defects enhance recombination of photo-excited carriers. In this paper, we systhemcaitlly report the defect properties of the prospective halide double perovskite semiconductors in comparison with their Pb analogues. We also suggest the optimal synthesis conditions for suitable conductivity and low deep defects, which are important for efficient solar cells.