Tunable electronic properties of TiO2 nanocrystals by in situ dopamine functionalization for planar perovskite solar cells

A high-quality TiO 2 electron transport layer (ETL) should possess a good energy-level alignment, perfect electron mobility, and excellent charge extraction efficiency. Nevertheless, the poor conductivity of amorphous TiO 2 film from low-temperature preparation is an inherent problem while the high-crystallined TiO 2 after high-temperature sintering (>450 °C) limits its application in the low-cost fabrication and flexible substrates. Here, we develop a low-temperature approach to in situ functionalize TiO 2 nanocrystals with dopamine molecules (DA-TiO 2 NCs) in the synthesis of the nanocrystals through a non-aqueous sol-gel method. We systematically investigate the tunable electronic properties of TiO 2 NCs with the variable DA modification and confirm that DA-TiO 2 can tailor the energy level alignment as well as increase the charge-extraction capacity, substantially reducing charge accumulation between the TiO 2 and perovskite layer. The in situ anchored amino groups (-NH 3 + ) not only preferentially boost the in-plane growth of perovskite grains but also induce the red-shift absorption of perovskite via the strong electrostatic interaction with Br − ions. Based on the DA-TiO 2 NCs ETLs, the power conversion efficiency of the fully ambient-processed planar FA x MA 1-x PbBr y I 3-y PSCs is optimized to 19.45%.