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.

In this work, a multi-electron transporting layer (ETL) for efficient perovskite solar cells is investigated. The multi-ETL consists of five conditions including SnO2, SnO2/SnOx, TiO2, TiO2/SnO2, and TiO2/SnO2/SnOx. The best performance of PSC devices is found in the SnO2/SnOx double-layer and exhibits a power conversion efficiency equal to 18.39% higher than the device with a TiO2 single-layer of 14.57%. This enhancement in efficiency can be attributed to a decrease in charge transport resistance (Rct) and an increase in charge recombination resistance (Rrec). In addition, Rct and Rrec can be used to explain the comparable power conversion efficiency (PCE) between a PSC with a SnO2/SnOx double-layer and a PSC with a triple-layer, which is due to the compensation effect of Rct and Rrec parameters. Therefore, Rct and Rrec are good parameters to explain the efficiency enhancement in PSC. Thus, the Rct and Rrec from the electrochemical impedance spectroscopy (EIS) technique is an easy and alternative way to obtain information to understand and characterize the multi-ETL on PSC.

Surface modification of Cs0.1(CH3NH3)0.9PbI3 is investigated by antisolvent‐assisted crystallization (ASAC). The perovskite solar cells (PSCs) of FTO/SnO2/Cs0.1(CH3NH3)0.9PbI3/spiro‐OMeTAD/Ag are also fabricated. It is found that isopropanol‐treated devices exhibit a power conversion efficiency (PCE) of 16.3%, which is higher than chlorobenzene‐ (11.5%) and toluene‐treated devices (12.8%). The efficiency enhancement by isopropanol treatment can be attributed to better surface coverage, larger grain size, and less pinholes confirmed by scanning electron microscopy (SEM) and X‐rays diffraction (XRD) results, indicating an increase in short‐circuit current density (Jsc). In addition, the increase in open‐circuit voltage (Voc) can be confirmed by photoluminescence (PL) spectra, which can be suggested to the reduce the nonradiative recombination loss in the isopropanol‐treated film. The wettability of perovskite films is studied by contact angle measurement, resulting in a higher hydrophobic surface from isopropanol‐treated devices. Also, the charge dynamic behavior of PSC devices is investigated by open‐circuit voltage decay (OCVD) measurement. It is found that the charge carrier lifetime of the isopropanol‐treated device is longer than that of chlorobenzene and toluene. Therefore, surface modification of perovskite by isopropanol treatment can enhance efficiency and isopropanol can be used as an alternative green antisolvent for the perovskite process.

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