The stabilization of black-phase formamidinium lead iodide (α-FAPbI3) perovskite under various environmental conditions is considered necessary for solar cells. However, challenges remain regarding the temperature sensitivity of α-FAPbI3 and the requirements for strict humidity control in its processing. Here we report the synthesis of stable α-FAPbI3, regardless of humidity and temperature, based on a vertically aligned lead iodide thin film grown from an ionic liquid, methylamine formate. The vertically grown structure has numerous nanometer-scale ion channels that facilitate the permeation of formamidinium iodide into the lead iodide thin films for fast and robust transformation to α-FAPbI3. A solar cell with a power-conversion efficiency of 24.1% was achieved. The unencapsulated cells retain 80 and 90% of their initial efficiencies for 500 hours at 85°C and continuous light stress, respectively.

Electron-transport-layer free perovskite solar cells (ETL-free PSCs) have attracted great attention due to their low cost and simple manufacturing process. However, an additional interface layer has to be introduced, and the currently achieved efficiency remains far from full-structure PSCs. Here, we report an in situ interface engineering strategy by the methylammonium acetate (MAAc) ionic liquid perovskite precursor. We found that a dipole layer was in situ constructed through the physical adsorption of the residual MAAc polar molecules on the indium tin oxide electrode, which is significantly different from the treatment by the interface layer in previous reports. This allows a decrease of the effective work function and enables in situ band bending in the perovskite semiconductor. The in situ band bending facilitates charge collection and hinders interfacial charge recombination, leading to ETL-free PSCs with a maximum power conversion efficiency of 21.08%, which is the highest report to date.

Organic−inorganic halide perovskites have attracted enormous attention for future optoelectronic applications because of their remarkable optical and electrical properties, solution processability, low cost, and large-scale fabrication capabilities. In addition to their use in photovoltaics and light-emitting diodes, halide perovskites have recently emerged as promising candidates for new-generation photodetectors. However, conventional three-dimensional halide perovskite photodetectors suffer from current−voltage hysteresis, unreliable performance, and instability. By controlling the morphological dimensionality of bulk three-dimensional and quasi-two-dimensional structured perovskites, low-dimensional halide perovskites (LDHPs, such as two-dimensional, one-dimensional, and zerodimensional halide perovskites), which have robust chemical stability and optoelectronic tunability owing to the quantum size effect, can be obtained, providing an alternative solution to overcoming the aforementioned limitations. In this Review, we examine the current state of the art and highlight the recent advances in photodetectors based on LDHPs, with a focus on their operation mechanisms, device architectures, synthesis and modification methods, and photodetection performances. We also discuss the current challenges for and provide a future perspective on the creation of LDHP-based photodetectors with unprecedented performance and opportunities for commercialization.

Photodetectors based on three dimensional organic–inorganic lead halide perovskites have recently received significant attention. As a new type of light-harvesting materials, formamidinium lead iodide (FAPbI3) is known to possess excellent optoelectronic properties even exceeding those of methylammonium lead iodide (MAPbI3). To date, only a few photoconductor-type photodetectors based on FAPbI3 single crystals and polycrystalline thin films in a lateral structure have been reported. Here, we demonstrate low-voltage, high-overall-performance photodiode-type photodetectors in a sandwiched geometry based on polycrystalline α-FAPbI3 thin films synthesized by a one-step solution processing method and post-annealing treatment. The photodetectors exhibit a broadband response from the near-ultraviolet to the near-infrared (330–800 nm), achieving a high on/off current ratio of 8.6 × 104 and fast response times of 7.2/19.5 μs. The devices yield a photoresponsivity of 0.95 AW−1 and a high specific detectivity of 2.8 × 1012 Jones with an external quantum efficiency (EQE) approaching 182% at −1.0 V under 650 nm illumination. The photodiode-type photodetectors based on polycrystalline α-FAPbI3 thin films with superior performance consequently show great promise for future optoelectronic device applications.

Ligand-free rutile and anatase TiO2nanocrystals were synthesizedviaa hydrolytic sol–gel method. The improved power conversion efficiency was achieved by using anatase TiO2nanocrystals as electron extraction layer in the organic solar cells.