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

Abstract

Recently, the rapid development of efficient organic-inorganic halide perovskite solar cells (PSCs) has been witnessed extensively. In this study, the TiO2 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 TiO2 NAs as electron transport and TiO2 compacted electron blocking layer were simultaneously grown on the fluorine-doped tin oxide glass. Zn-doped TiO2 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 TiO2 NAs are investigated methodically. The reduced contact angle shows the enhanced affinity of Zn-doped TiO2 with perovskite. Study shows that Zn-doped TiO2 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 TiO2 NAs ETL exhibits higher electron mobility than that of pristine TiO2 NAs. The increased in Jsc of the Zn-doped TiO2 NAs based cells is mainly ascribed to the reduced trap-state density and enhanced electrical conductivity. As compared with the flat band potential (VFB) of pristine sample, the VFB of 2.5 mol% Zn-doped TiO2 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.