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In this work, interface modification of SnO2 layer using p–n junction double layer is investigated for the efficiency enhancement of perovskite solar cell (PSC). For the double layer, a Sn additive layer was applied on a SnO2 layer by using the DC magnetron sputtering technique at various deposition times. The highest power conversion efficiency of 15.11% is obtained for PSC with a SnOx additive layer at 5 s sputtering time, compared to 12.89% for the best PSC without the additive layer. The effect of the SnOx additive layer on PSCs at optimum sputtering time is further explored via the photoconversion properties of both optical and electrical properties. From the results, it is found that the SnOx additive layer is essential for efficiency enhancement by forming the p-n junction with a SnO2 electron transporting layer (ETL) and modifying the interface between the ETL and the perovskite layer. The p-n junction of the ETL is observed via the diode-like behavior of I–V characteristics. The interface modification can enhance the PSC efficiency by improving the quality of the perovskite layer due to the larger grain size and higher absorbance, and by improving the charge transfer. The faster photogenerated charge transfer is confirmed by lower PL intensity and the shorter charge transfer lifetime is confirmed by the fitted open-circuit voltage decay. In addition, the SnOx additive layer can also eliminate the hysteresis effect of PSCs. This interface modification technique for PSC efficiency enhancement could be further explored for other ETLs.

Black titanium dioxide (TiO2) quantum dots (QDs) are grown by a solution‐based electrochemical process and an effect of KCl concentration on the growth is investigated. The electrochemical process is demonstrated as a simple one‐step process for the growth of black TiO2 QDs in the solutions via bottom–up process. From the absorption spectra, the absorption appears for an entire visible wavelength (400–700 nm) implying a black TiO2 property. The average size of the black TiO2 QDs is about 4.5 nm from the transmission electron microscopy results and is similar to all KCl concentrations. This indicates that KCl concentration has no effect on the particle size, but has effect on the hydrodynamic size of TiO2 QDs. The black TiO2 QDs can be produced by the hydrogenation process of hydrogen ions during electrochemical process. The obtained black TiO2 QDs can be further explored as an electron‐transporting layer for a perovskite solar cell application.

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