Optimization of TiO2/ZnO bilayer electron transport layer to enhance efficiency of perovskite solar cell

In the present study, TiO2/ZnO bilayer as electron transport layer is optimized and used to design a perovskite solar cell. This bilayer helps in high electron extraction and low interfacial recombination. TiO2 films are prepared using spray pyrolysis techniques on fluorine doped tin oxide substrate. The deposition parameters are optimized using parametric study as well as using the Taguchi optimization technique. ZnO is used as other part of electron transport bilayer to reduce the charge recombination. The thickness of prepared TiO2 film obtained at Taguchi optimum condition (103 nm) is lower than that of obtained at parametric optimum condition (147 nm). At optimum conditions, the optical band gaps are in the range of 3.20-3.25 eV. The prepared TiO2 films are consequently applied in perovskite solar cell preparation. 4-tert-butylpyridine is used with PbI2 to increase the stability of the perovskite solar cell. In addition, spiro-OMeTAD and Pt-fluorine doped tin oxide are used as hole transport material and counter electrode, respectively. The power conversion efficiency of the device at optimum conditions (parametric (D-5) and Taguchi (D-9)) has been found as 5.59% and 6.51%, respectively. The power conversion efficiency of the device using 4-tert-butylpyridine as stabilizer has been found as 7.39% (D-11), which is highest among all devices. Current density (J(sc)), open circuit voltage (V-oc) and the fill factor obtained for the device (D-11) are 17.87 mA cm(-2), 0.65 V, and 64%, respectively.