Dr. Ashraf Uddin
Associate Professor, School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, Australia

Biography: Ashraf Uddin obtained his PhD degree in March 1991 in Semiconductor Physics from the Osaka University, Osaka, Japan. After his PhD he joined at the R&D centre of Toshiba Corporation, Japan and worked on opto-electronic devices and on poly-Si thin film transistor to develop a process technology on glass substrate for the fabrication of flat panel display (LCD type). He worked at the School of Materials Science and Engineering (MSE), Nanyang Technological University (NTU), Singapore. Now, he is working on organic and perovskite solar cells in the School of Photovoltaic and Renewable Energy Engineering, University of New South Wales (UNSW) as an Associate Professor since January 2009. He has published over 200 journal papers and has several patents on semiconductor devices.

Speech Title: Low temperature processed sol-gel ZnO for high efficiency perovskite solar cells

Abstract:Organic–inorganic hybrid perovskite solar cells (PSCs) are promising candidates for the low cost photovoltaic technology with certified power conversion efficiency (PCE) over 22.7%. The reported high efficiency PSCs are needed high temperature processes because of electron transport layer (ETL) TiO2. The low temperature processed PSCs are needed for the commercial production in a roll-to-roll process on flexible substrates. Low temperature solution process zinc oxide (ZnO) is one of the suitable materials and the solution of low temperature processing of PSCs. However, due to a relatively open, hexagonal close-packed lattice structure of ZnO, its (ZnO’s) unoccupied octahedral sites act as defect states within its bandgap, which act as recombination centres for the photo-generated electrons from the perovskite conduction band and affects the device performance. Low temperature (140 ⁰C) spin-coating deposition processes was developed for ETL and optimize the sol-gel ZnO thin-film thickness to improve the device performance. To solve the energetic-disorder induced trap-states in low-temperature processed ZnO film, both bulk and surface modification of sol-gel ZnO ETL were improved. The bulk modification of ZnO film via metal (Al, Cs, Li) doping passivates the interstitial vacancies in host ZnO lattice matrix. As a form of surface modification, ultra-violet ozone treatment was applied on ZnO surface, which simultaneously passivated the interstitial as well as oxygen vacancy mediated vacancies in ZnO for enhanced device performance. Overall, the fabricated PSCs demonstrate a maximum PCE of 18% and retain about 90% normalized efficiency even after a month of degradation study without encapsulation. Detailed optical, structural and electro-chemical characterizations were conducted to understand the underlying mechanisms governing the enhancement in PCE, stability and photo-current hysteresis in sol-gel ZnO ETL based perovskite devices. I will present all of our above detail results on our investigation and discuss in the conference presentation.