Properties of perovskite solar cells with GO addition on TiO₂ layer

The photovoltaic properties of perovskite solar cells (PSCs) were investigated by adding graphene oxide (GO) to the electron transport layer of TiO₂. The PSCs were fabricated with a glass/FTO/BL-TiO₂/meso-TiO₂ + GO/perovskite/HTL/Au electrode structure by adding various contents of GO (0.0, 0.3, 0.5 and 0.7 wt%) to the TiO₂ layer. To analyze the photovoltaic characteristics and transmittance of the TiO₂ layer of the PSCs according to the GO content, solar simulator and ultraviolet-visible-near-infrared spectroscopy were used, respectively. Atomic force microscopy and field emission scanning electron microscope were used to analyze the microstructures of both the TiO₂ layer and the perovskite layer. The results of the photovoltaic characteristics indicated that energy conversion efficiency (ECE) was gradually increased to 12.70%, 13.13%, 14.19%, and 12.63% for 0.0, 0.3, 0.5, and 0.7 wt% GO contents, respectively. The highest ECE was observed at a GO content of 0.5 wt%, and a decrease in the ECE was confirmed at higher levels. The increase in ECE was confirmed by measuring short circuit current density (J_sc) and shunt resistance which increased with the GO addition. However, when an excessive amount of GO content was added, a decrease in the ECE was observed, due to the decrease in J_sc by the reduction in transmittance. In particular, an increase in the perovskite crystal size caused an increase in the ECE, due to the increased rms of TiO₂ at 0.5 wt% GO. With the 0.7 wt% GO TiO₂ layer, the perovskite grain size was decreased by the reduction in rms, and this resulted in a decrease in J_sc and ECE. These results suggest that we might improve the efficiency of perovskite solar cells by adding the proper amount of GO to the TiO₂ layer.