Abstract
Vapour deposition of metal halide perovskite by co-evaporation of precursors has the potential to achieve large-area high-efficiency solar cells on an industrial scale, yet little is known about the growth of metal halide perovskites by this method at the current time. Here, we report the fabrication of MAPbI3 films with average thicknesses from 2-320 nm by co-evaporation. We analyze the film properties using X-ray diffraction, optical absorption and photoluminescence (PL) to provide insights into the nucleation and growth of MAPbI3 films on quartz substrates. We find that the perovskite initially forms crystallite islands of around 8 nm in height, which may be the cause of the persistent small grain sizes reported for evaporated metal halide perovskites that hinder device efficiency and stability. As more material is added, islands coalesce until full coverage of the substrate is reached at around 10 nm average thickness. We also find that quantum confinement induces substantial shifts to the PL wavelength when the average thickness is below 40 nm, offering dual-source vapour deposition as an alternative method of fabricating nanoscale structures for LEDs and other devices.
Highlights
Metal halide perovskites with the formula ABX3, (where A is a cation such as cesium or methylammonium, B is usually lead, and X is a halide) have attracted much interest due to their ease of fabrication,[1] widely tunable direct optical band gap,[2,3,4,5] and exceptional electronic properties.[6,7] They have been successfully employed in solar cells,[8,9,10,11] resulting in certified power conversion efficiencies (PCE) over 22%,10 and have proved effective in other optoelectronic devices such as light emitting diodes (LEDs)[12,13,14] and lasers.[15,16] One advantage of these materials is that they can be fabricated by a variety of methods[1] including spin coating, a method which enables quick and easy fabrication of small scale samples in the laboratory
We determined the thickness by matching the optical absorption between 550 nm and 700 nm to the absorption coefficient previously determined for identically fabricated MAPbI3 in this wavelength range[18]
We have demonstrated that photoluminescence from the thinnest MAPbI3 films fabricated by vapour deposition is dominated by quantum confinement, which promises to be a useful fabrication method for nanoscale structures that can be implemented in efficient light emitting diodes (LEDs)
Summary
Metal halide perovskites with the formula ABX3, (where A is a cation such as cesium or methylammonium, B is usually lead, and X is a halide) have attracted much interest due to their ease of fabrication,[1] widely tunable direct optical band gap,[2,3,4,5] and exceptional electronic properties.[6,7] They have been successfully employed in solar cells,[8,9,10,11] resulting in certified power conversion efficiencies (PCE) over 22%,10 and have proved effective in other optoelectronic devices such as light emitting diodes (LEDs)[12,13,14] and lasers.[15,16] One advantage of these materials is that they can be fabricated by a variety of methods[1] including spin coating, a method which enables quick and easy fabrication of small scale samples in the laboratory. We find that quantum confinement induces substantial shifts to the PL wavelength when the average thickness is below 40 nm, offering dual-source vapour deposition as an alternative method of fabricating nanoscale structures for LEDs and other devices.
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