Boosting the efficiency of commercial available carbon-based perovskite solar cells using Zinc-doped TiO2 nanorod arrays as electron transport layer

Recently, the rapid development of efficient organic-inorganic halide perovskite solar cells (PSCs) has been witnessed extensively. In this study, the TiO 2 nanorod arrays (NAs) with different molar ratios of zinc doping were employed as electron transport layer in carbon-based perovskite solar cells for enhancing photovoltaic performance . Zinc-doped TiO 2 NAs as electron transport and TiO 2 compacted electron blocking layer were simultaneously grown on the fluorine-doped tin oxide glass . Zn-doped TiO 2 NAs show the vertical growth on FTO surface with good crystallinity which provides the direct pathway for the perovskite penetration and the better carrier transfer performance. The surface morphology , crystal structure, absorption and electrical conductivity of Zn-doped TiO 2 NAs are investigated methodically. The reduced contact angle shows the enhanced affinity of Zn-doped TiO 2 with perovskite. Study shows that Zn-doped TiO 2 based PSC device has higher shunt resistance and low series resistance and longer carrier lifetime when compared with pristine sample. The space-charge-limited current (SCLC) measurement demonstrates that 2.5 mol% Zn-doped TiO 2 NAs ETL exhibits higher electron mobility than that of pristine TiO 2 NAs. The increased in J sc of the Zn-doped TiO 2 NAs based cells is mainly ascribed to the reduced trap-state density and enhanced electrical conductivity. As compared with the flat band potential (V FB ) of pristine sample, the V FB of 2.5 mol% Zn-doped TiO 2 NAs has a negative shift of 0.33V, thus resulting in the positive shift of conduction band and better band alignment with perovskite layer. The power conversion efficiency was improved from 12.99% to 14.45% with the optimized zinc doping concentration of 2.5 mol%. Furthermore, the optimized cell without encapsulation still maintains 85% of original efficiency via 30 days stability test.