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The hybrid (organic-inorganic) Perovskite materials have recently received a significant interest amongst research groups across the world. These materials reveal such outstanding semiconductor properties as very high absorption coefficient, tuneable and direct bandgap, diffusion length of charge carriers exceeding 1 µm, ease and lower cost of processing and others. Particularly, the perovskite solar cells have shown an unprecedented growth in power conversion efficiency from 3.8 % to over 22% within a short span of time (NREL best research-cell efficiencies chart ).
Figure (a) Perovskite structure of CH3NH3PbI3 (commonly used). Methylammonium cation (CH3NH3+) occupies the central A site surrounded by 12 nearest-neighbour iodide ions in corner-sharing PbI6 octahedra (Image : By Christopher Eames et al. [CC BY 4.0 ], via Wikimedia Commons). (b) Number of published articles on Perovskite. The counts were obtained using the keywords “Perovskite” + “Solar” and “Perovskite” + ‘Devices” in the ISI Web of Science (Thomson Reuters) portal for search field “Topic”. (c) Simplified schematic of some of the common Perovskite device architectures for the solar cell, photodiode, photoconductor, and phototransistor (HTL: Hole Transport Layer, ETL: Electron Transport Layer, TCO: Transparent Conductive Oxide).
Despite many advantages, Perovskites still face challenges and drawbacks, such as degradation due to external factors like moisture, oxygen, elevated temperature, UV light. Due to the high compositional and structural flexibility, hybrid Perovskites demonstrate general defectiveness, active ion migration, spatial inhomogeneity, interfacial reactions and phase transitions at working conditions. Commercialization of Perovskite optoelectronic device is only viable when these limitations and drawbacks are overcome. It is then vital to understand and control the processes of formation, crystallisation and degradation being able to enhance stability of Perovskites and interfaces in the devices.
The Perovskite research in TFD is focused on the design and fabrication of optoelectronic devices combining knowledge from wet chemistry and expertise from plasma technologies. New materials and architectures are being explored for realizing state of the art devices. The objectives of the current research and development are as follows:
- Growth of Perovskite single crystal-like thin-films from the precursor solutions
- Understanding the stability of various Perovskite materials by Raman and PL spectroscopy
- Use of Carbon based nanomaterials for improving the Perovskite interfaces
- Development of metal oxide charge selective layers for Perovskite devices
- Development of alternative Perovskite crystallization and annealing techniques
- Model-based characterization of sputter damage and material development of TCO for Si/Perovskite tandem solar cells and device implementation
- Development of the soft-deposition p-TCOs for CIGS/Perovskite monolithic tandem cell