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

Abstract A high-quality TiO2 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 TiO2 film from low-temperature preparation is an inherent problem while the high-crystallined TiO2 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 TiO2 nanocrystals with dopamine molecules (DA-TiO2 NCs) in the synthesis of the nanocrystals through a non-aqueous sol-gel method. We systematically investigate the tunable electronic properties of TiO2 NCs with the variable DA modification and confirm that DA-TiO2 can tailor the energy level alignment as well as increase the charge-extraction capacity, substantially reducing charge accumulation between the TiO2 and perovskite layer. The in situ anchored amino groups (-NH3+) 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-TiO2 NCs ETLs, the power conversion efficiency of the fully ambient-processed planar FAxMA1-xPbBryI3-y PSCs is optimized to 19.45%.