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

Highlights: • Zn–TiO₂ nanorod with good crystallinity were faultlessly vertically grown on FTO surface. • Commercial available carbon and CuSCN were used in perovskite solar cell. • Zn dopant not only enhances the electrical conductivity but also decreases the trap density of TiO₂ NAs. • The optimized device obtained PCE of 14.45% and maintains 85% of original efficiency without encapsulation within 30 days. -- 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 J_sc 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 (V_FB) of pristine sample, the V_FB 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.