Periodic Reporting for period 1 - PEROPTO (Single Crystalline Halide Metal Perovskites Based Optoelectronics) Reporting period: 2018-02-01 to 2020-01-31 Summary of the context and overall objectives of the project The emerging methylammonium lead halide perovskite are the ideal materials of specific interest for diverse optoelectronic applications, for instance, photovoltaic, light emitting diode (LED), laser and photodetector, etc. Especially in the field of photovoltaics, the photo-to-electron conversion efficiency of perovskite solar cells (PSCs) has rapidly risen from 3.8% to 22.1% within a few years. According to the literature, the nature of polycrystalline perovskite films as the main absorbing layer of PSCs intrinsically impedes further improvement of cell performance due to the fact that tremendous amount of grain boundaries and defects existing within polycrystalline perovskite films serves as recombination center and thus hinders efficient diffusion of charge carriers, which confines diffusion length of charge carriers within only few micrometers. Therefore, breakthrough improvement of its efficiency will rely decisively on the finest control or minimize grain boundaries and trap densities of perovskite materials, which eventually could be single crystalline perovskite materials. Among various morphologies of perovskite single crystals, ultrathin large scale perovskite platelets, which have the shape with much-extended dimension up to centimeters scale along x, y-direction but confined dimension down to less than 1 µm in z-direction, possess the practical potential for fabricating high-performance optoelectronic devices. This proposal will tackle with the synthetic challenges of single crystalline perovskite materials with controllable dimension and its integration with optoelectronic devices such as solar cell, LED and laser for potential breakthrough of device performance. This envisioned combined approach, as far as we know, is herein explored for the first time.In this project, we are planned firstly tackle with synthetic obstacles obtaining those single crystals with tailored dimension, especially ultrathin large scale perovskite platelets, by either chemical solution process which takes advantage of template formed by specific metal oxide frame or functional surfactants, or spatial atmospheric atomic layer deposition process which requires an epitaxial growth by feeding specific precursor vapor of perovskite raw materials. With those materials in hand, various optoelectronic devices, especially solar cell as the initial attempt, will be constructed based on those synthesized large scale single-crystalline perovskite materials for a potential breakthrough of device performance, and characterized with advanced optical and electronic tools and techniques to correlate device performance with the nature of single crystalline perovskite materials. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far According to our plan, the solution chemistry is adapted to fulfill the preparation of controlled dimensional single crystalline perovskite materials proposed in this project.1. Ultra thin perovskite platelet:The method proposed is based on the synthesis of specific surfactants from their precursors alkyl ammonium salts and halide acid solution by chemical solution process. Different types of surfactants, basically block-copolymers with varied length of carbon chain and functional end group as well, could impede or guide growth of perovskite crystal at certain direction, such as dodecylammounium iodide (DOD) (Task 2.1) preferentially binds the halide ions of (001) facets and then results in platelet-like perovskite single crystals, while octadecylammonium iodide (OTD) (Task 2.2 in the proposal) selectively binds the halide ions of (110) or (1–10) crystal facets and thus impedes the growth of the two directions and gives rise to wire-like perovskite single crystals, as shown in Figure 1 of the technical report. The solubility of synthesized supramolecular surfactants in perovskite precursor solution will be further adjusted by anchoring different functional end group (Task 2.3). Further purification of surfactants is crucial and will be done by recrystallization or filtration (Task 2.4). Their structural and compositional characterization will be done by different techniques such as X-ray diffraction, NMR and electron microscopies (Task 2.5). The synthesized platelets are shown in Figure 2 of the technical report.2. Bulk perovskite single crystals:At the same time, we are also carrying out the experiments to synthesize bulk perovskite single crystals, as shown in Figure 3 of the technical report. The method of solvothermal method is adapted to grow bulk perovskite single crystals, which just utilize the solubility difference of perovskite materials in polar solvent under different temperature. Currently, the centimeter-size perovskite single crystals is prepared and will be analyzed by some optical and electrical facilities based in Cambridge. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) The nature of polycrystalline perovskite films as the main absorbing layer of PSCs intrinsically impedes further improvement of cell performance due to the fact that tremendous amount of grain boundaries and defects existing within polycrystalline perovskite films serves as recombination center and thus hinders efficient diffusion of charge carriers, which confines diffusion length of charge carriers within only few micrometers. Therefore, breakthrough improvement of its efficiency will rely decisively on the finest control or minimize grain boundaries and trap densities of perovskite materials, which eventually could be single crystalline perovskite materials. Although perovskite materials based optoelectronics are recognized to be of great potential and the research in them is intense, none of the papers so far reported deals with the possibility of coupling the single crystalline perovskite with optoelectronic devices to further increase the device performance, as proposed in this project. In this context, the proposal herein presented deals with a highly innovative approach that we believe comes in timely.This project is tackling with the synthetic challenges of single crystalline perovskite materials with controllable dimension and its integration with optoelectronic devices such as solar cell, LED and laser for potential breakthrough of device performance. This envisioned combined approach, as far as we know, is herein explored for the first time.Currently, we are able to produce perovskite thin platelet with thickness about few tens nanometers to few micrometers, as shown in Figure 2, which will is currently applied to some optoelectronics devices such as filed effect transistors as shown in Figure 3, that may have interesting advance in its performance due to implantation of single crystalline perovskite The bulk perovskite single crystals synthesized in this project Perovskite platelets synthesized in this project during the first year The perovskite platelets are transferred onto the electrode to fabricate the devices such as FET Perovskite single crystal prepared by templating method with the help of specific surfactants
