4.3. Analysis
A field emission scanning electron microscope (FE-SEM, SU-70, Hitachi) was used to examine the morphology and thickness of the device configurations while an X-ray diffractometer (Rigaku Corp., D/max-2500, Tokyo, Japan) was used to confirm the crystallinity of TiO2 and perovskite layers. To measure the transmittance, a UV-Vis spectrophotometer (Jasco International Co., Ltd., V-730, Tokyo, Japan) was used and the infrared spectra were recorded on the Fourier-transform infrared (FTIR) spectrometer (Nicolet 6700, Thermo Scientific) in the range of 600 – 4000 cm-1. Then, a solar simulator (Newport Corp., Model 94022A, Irvine CA, USA) with a source meter (Keithley Instruments Inc., Keithley 2400, Cleveland, OH, USA) under AM 1.5 illumination (100 mW/cm2) was used to characterize the photovoltaic properties of PSCs. The characterization was carried out at the Future Energy Convergence Core Center (FECC). All devices were measured by masking 0.1256 cm2 of the active area with a mask under argon condition. The solar cell quantum efficiency measurement system (PV Measurements Inc., QEX7, Point Roberts, WA, USA) was also used to measure the incident photon to electron conversion efficiencies. Electrochemical impedance spectroscopy was performed using a potentiostat (Solartron 1287) and frequency response analyzer (Solartron 1260) in the range of 10-2 and 106Hz. The measurements were analyzed using the ZView software (Solartron Analytical) with the aid of appropriate equivalent circuit, where the applied bias voltage and the amplitude of alternating current was set at the open circuit voltage (Voc ). The impedance measurements were carried out at open-circuit potential under AM 1.5 illumination.