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Both TiO 2 and SnO 2 as electron transport layers (ETLs) are the most successful at producing high-efficiency perovskite solar cells (PSCs). Unfortunately, these layers usually require multiple treatments to improve device performance, especially for TiO 2 -based planar PSCs. Here, a simple, one-step, solution-based method is introduced for fabricating a TiO 2 /SnO 2 nanocomposite ETL. Compared to a pristine TiO 2 layer, partial incorporation of SnO 2 nanoparticles in a thin compact TiO 2 layer contributes to high electrical conductivity and suitable band-level alignment at the ETL/perovskite interface. Using the optimized TiO 2 /SnO 2 nanocomposite ETL, methylammonium lead halide perovskite CH 3 NH 3 PbI 3 -based PSCs exhibit the champion efficiency of 16.8% (area, 0.13 cm 2 ) with less current density−voltage (J−V) hysteresis, which is significantly superior to that of TiO 2 -based PSCs. Our work highlights that the successful use of TiO 2 /SnO 2 nanocomposite ETL can offer an efficient method for further improvement of the performance for planar PSCs.

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The reverse mortgage is a very useful financial product for senior citizens who own homes but do not have a cash income, while it is a high-risk product from the lender's perspective. One of benefits of reverse mortgages is that the debt limit is restricted to the scope of the disposition price of the collateralized house, which is considered a put option to borrowers. The present study evaluates the option value of the reverse mortgage in Hong Kong through an empirical analysis using the Black-Scholes option-pricing model. Moreover, the present study shows specific monetary values through option matching to the consumer situation, contributing to the increased understanding of reverse mortgages from the consumer's point of view.