Self-assembled polar hole-transport monolayer for high-performance perovskite photodetectors

Abstract

A self-assembled polar monolayer (SAPM) is proposed to serve as the hole-transport layer (HTL) in optoelectronic devices. To illustrate our working principle, a superior performance of organic–inorganic halide perovskite (OIHP) photodetectors and solar cells is reported. A monolayer of poly[3-(6-carboxyhexyl)thiophene-2,5-diyl] (P3HT–COOH) was prepared on an ITO anode through a self-assembled process as HTL. It was found that the self-assembled P3HT–COOH monolayer exhibited a preferential dipole orientation on the ITO and possessed an electric field pointing toward the ITO side, which produced a positive shift of lowest-dark-current-density bias and a reduced work function relative to the spin-coated film. The presence of this internal electric field in OIHP photodetectors facilitates charge collection and assists carrier transport. Additionally, the higher LUMO level of SAPM could effectively block electron injection and lower the dark current density in comparison with that made from spin-coated P3HT–COOH. As a result, an OIHP photodetector with SAPM as the HTL demonstrated a detectivity of more than 3.03 × 10¹³ cm Hz^1/2 W⁻¹, a response time of 95 ns, a responsivity of 0.479 AW⁻¹, and a stable responsivity over 11 decades. Moreover, solar cells based on SAPM exhibit much better power conversion efficiency than conventional PEDOT:PSS-based devices. All these outstanding results can be extended to many other material systems, which ensure that our approach represents a key step toward the advancement in the development of cost-effective and high-performance semiconductor optoelectronic devices.