Medical X-ray imaging procedures require digital flat detectors operating at low doses to reduce radiation health risks. Solution-processed organic-inorganic hybrid perovskites have characteristics that make them good candidates for the photoconductive layer of such sensitive detectors. However, such detectors have not yet been built on thin-film transistor arrays because it has been difficult to prepare thick perovskite films (more than a few hundred micrometres) over large areas (a detector is typically 50 centimetres by 50 centimetres). We report here an all-solution-based (in contrast to conventional vacuum processing) synthetic route to producing printable polycrystalline perovskites with sharply faceted large grains having morphologies and optoelectronic properties comparable to those of single crystals. High sensitivities of up to 11 microcoulombs per air KERMA of milligray per square centimetre (μC mGy cm) are achieved under irradiation with a 100-kilovolt bremsstrahlung source, which are at least one order of magnitude higher than the sensitivities achieved with currently used amorphous selenium or thallium-doped cesium iodide detectors. We demonstrate X-ray imaging in a conventional thin-film transistor substrate by embedding an 830-micrometre-thick perovskite film and an additional two interlayers of polymer/perovskite composites to provide conformal interfaces between perovskite films and electrodes that control dark currents and temporal charge carrier transportation. Such an all-solution-based perovskite detector could enable low-dose X-ray imaging, and could also be used in photoconductive devices for radiation imaging, sensing and energy harvesting.

For scalable perovskite solar cells (PSCs), deposition of a homogeneous and high-quality perovskite film on a large area (>100 cm 2 ) is a prerequisite. Conventional solutions for spin-coating on small areas usually contain polar aprotic solvents with high boiling point, which is difficult to adopt for large-area bar coating because of the uncontrollable and slow drying process due to the strong interaction between polar aprotic solvent and Lewis acidic PbI 2 or perovskite. Thus, the precursor solution plays a vital role in the success of largearea coating. Here we report a coating solution suitable for large-area perovskite films. The coating solutions prepared via gas-mediated solid−liquid conversion contain preformed perovskite clusters as confirmed by rotational mode of methylammonium cation in the PbI 3 − framework from Raman spectroscopy. CH 3 NH 3 PbI 3 (MAPbI 3 ) films formed by D-bar coating within 20 s on the area over 100 cm 2 exhibit tetragonal/cubic superlattice structure with highly preferred orientation in the entire film, which results in average power conversion efficiency (PCE) of 17.01% and best PCE of 17.82%.

Here, we report on precursor engineering for a large-area perovskite film using an air-knife-assisted D-bar coater. Lead acetate (PbAc2) is stoichiometrically added in the mother solution consisting of methylammonium iodide (MAI) and lead iodide (PbI2) in 2-methoxyethanol (2ME), leading to MAPbI3 and byproduct methylammonium acetate (MAAc). Crystal growth can be controlled in the presence of MAAc while drying the wet film. An average power conversion efficiency (PCE) of 15.14% is achieved, whereas the quality of the perovskite film is uncontrollable in the absence of PbAc2, resulting in a PCE as low as 2.63%. Carrier lifetime is further improved by about 46% when incorporating 0.12 mol % guanidinium iodide (GAI) in the PbAc2-containing precursor solution, which demonstrates a PCE of 19.44% with a device employing a piece of the large-area perovskite film (∼46 cm2) and a PCE of 13.85% with a module with an active area of 16 cm2.

With the impressive record power conversion efficiency (PCE) of perovskite solar cells exceeding 23%, research focus now shifts onto issues closely related to commercialization. One of the critical hurdles is to minimize the cell-to-module PCE loss while the device is being developed on a large scale. Since a solution-based spin-coating process is limited to scalability, establishment of a scalable deposition process of perovskite layers is a prerequisite for large-area perovskite solar modules. Herein, this paper reports on the recent progress of large-area perovskite solar cells. A deeper understanding of the crystallization of perovskite films is indeed essential for large-area perovskite film formation. Various large-area coating methods are proposed including blade, slot-die, evaporation, and post-treatment, where blade-coating and gas post-treatment have so far demonstrated better PCEs for an area larger than 10 cm 2 . However, PCE loss rate is estimated to be 1.4 × 10 −2 % cm −2 , which is 82 and 3.5 times higher than crystalline Si (1.7 × 10 −4 % cm −2 ) and thin film technologies (≈4 × 10 −3 % cm −2 ) respectively. Therefore, minimizing PCE loss upon scaling-up is expected to lead to PCE over 20% in case of cell efficiency of >23%.

Since the first report on solid-state perovskite solar cells (PSCs) with ∼10% power conversion efficiency (PCE) and 500 h-stability in 2012, tremendous effort has been being devoted to develop PSCs with higher PCE, longer stability and recycling hazardous lead waste. As a result, PCE over 23% was recorded in 2018 and stability over 10 000 h was reported. Beyond photovoltaics, lead halide perovskite materials demonstrated superb properties when they were applied to flat-panel x-ray detectors and non-volatile resistive switching memory. In this review, the progress of the lead halide perovskite in photovoltaics, x-ray imaging and memristors is investigated. Pb-based PSCs and non-Pb-based PSCs are compared, where technologies of non-Pb-based PSCs are not matured for commercialization. Pb-based PSCs were found to be highly suitable for both terrestrial and space photovoltaics. Higher sensitivity under low dose rate observed from the lead halide perovskite suggests a bright future for perovskite x-ray imaging systems. Moreover, high on/off ratio and low energy consumption observed in resistive switching enables perovskite to be a promising candidate for high density memristors.