Engineering Sciences

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Objective: LED 1) The objective of the proposal is the rational design of highly fluorescent, optical tunable and stable all-inorganic hybrid double perovskite materials (eg. Cs2AgInCl6 and Cs2AgBiBr6) and to study their optoelectronic properties towards white light emission for LED applications. 2) Studies on the influence of crystallographic distortion (Jahn-Teller) on the self-trapped excitons (STEs) and the luminescence properties of the double perovskites. 3) Laboratory scale fabrication and demonstration of a white light LED from the synthesized double perovskites. Studies on the stability and color coordinates of the white light emitting perovskites. PSC 1) Material engineering for more stable, less toxic and efficient perovskite solar cells ? Synthesis of conventional and new perovskite materials, lead-free perovskites, lower dimension perovskitesetc ? Development of compatible hole transporting and electron transporting materials 2) Developing formulations for spin coating/doctor blading/screen printing of electron transport layers, perovskite layers, insulating layers and carbon electrodes. 3) Perovskite solar cell fabrication employing mesoscopic architecture with metal contact and metal free back electrode and optimization with standard/in-house materials (Target ?>15%) 4) Detailed interfacial electrical characterizations involving Electrochemical Impedance Spectroscopy (EIS), Photomodulatedimpedenace (IMVS, IMPS), Charge extraction (CE), OCVD and current transients (CT) to probe transport and recombination. 5) Device engineering to improve long term stability and scalability 6) Transforming the research activity from TRL1 ? TRL4 by interdisciplinary team work

Summary: Recent research and developments indicate the promising future of lead-free perovskites for broadband white light emitting diodes (WLED), especially as single emitter layer phosphors to replace traditional rare earth elements. Recently, DPs with general formula A2MM'X6 and in particular Cs2AgBiCl6 as one of the few materials investigated for the warm white light emission with good stability. This type of photon emission with energies distributed across the whole visible spectrum is ascribed to the radiative decay of self-trapped excitons (STEs), but the mechanism is not very much clearly understood and needs more in depth studies. Also, there is very little known about the impact of crystallography upon the optoelectronic properties for such compounds. So understanding of the phenomenon on this class of DPs which represent a very good model system is important both in order to improve the properties of the present family of DPs and to design new compounds. So the main objective of this proposal is rational design of highly fluorescent, optical tunable and air stable all-inorganic hybrid DPs (eg. Cs2AgInCl6 and Cs2AgBiBr6) and study their optoelectronic properties for WLED applications. The present project also involves development ofscreen printable formulations of electron transport layers (TiO2), perovskite layers (lead halides and lead free), and carbon electrodes which are highly required to take the PSC research to commercial grounds. We also aim to come up with a catalogue of lead-based and lead-free perovskite materials and hole transporting materials which are cost effective and scalable. Fabrication of lab-scale small area devices (0.10~0.20 cm2) will be carried out employing mesoscopic architecture with metal contacts, achieving efficiencies up to >15% with standard materials which will further be extended to our homemade materials. Deeper understanding of structure-optoelectronic, property-device performance will be evaluated through structural, photophysical, morphological, charge transport studies supported with device dynamic measurements.

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