Crystallinity and crystal orientation have a predominant impact on a materials’ semiconducting properties, thus it is essential to manipulate the microstructure arrangements for desired semiconducting device performance. Here, ultra‐uniform hole‐transporting material (HTM) by self‐assembling COOH‐functionalized P3HT (P3HT‐COOH) is fabricated, on which near single crystal quality perovskite thin film can be grown. In particular, the self‐assembly approach facilitates the P3HT‐COOH molecules to form an ordered and homogeneous monolayer on top of the indium tin oxide (ITO) electrode facilitate the perovskite crystalline film growth with high quality and preferred orientations. After detailed spectroscopy and device characterizations, it is found that the carboxylic acid anchoring groups can down‐shift the work function and passivate the ITO surface, retarding the interface carrier recombination. As a result, the device made with the self‐assembled HTM show high open‐circuit voltage over 1.10 V and extend the lifetime over 4,300 h when storing at 30% relative humidity. Moreover, the cell works efficiently under much reduced light power, making it useful as power source under dim‐light conditions. The demonstration suggests a new facile way of fabricating monolayer HTM for high efficiency perovskite devices, as well as the interconnecting layer needed for tandem cell.

Control of interface properties is one of the important issues in optimizing the performance of hybrid polymer–metal-oxide solar cells. We select a soluble conductive small molecule, 2-naphthalenethiol (2-NT), to modulate the surface properties of the oriented ZnO-nanorod arrays before contacting with the polymer blend in an inverted hybrid solar cell configuration. This conductive molecule enhances the compatibility between polymer blend and metal-oxide, enlarges the exciton separation efficiency and subsequent charge transfer rate into the bulk of nanorods by the bond dipole field, reduces interfacial recombination and improves the ordering of charge transport network. As a result, there is a substantial improvement in photocurrent, open circuit voltage and fill factor leading to double the power conversion efficiency of the unmodified device from 1.86% to 3.71%. This value sets the record for the highest efficiency reported to date based on ITO/ZnO-nanorod/poly(3-hexythiophene):(6,6)-phenyl C₆₁ butyric acid methyl ester (P3HT:PCBM)/Ag configuration.

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.