- This event has passed.
Talk: Role of Cu deficient layer in chalcopyrite based solar cells
April 25, 2019 from 11:00 am — 12:00 pm
IEC seminar by Abhishek Sharan
Chalcopyrites are a demonstrated material platform for realizing efficient thin-film photovoltaics, with the most well-known Cu(In,Ga)Se2 (CIGS) based solar cells exceeding 23%. Several factors, including flexibility in tuning the absorber band gap, enhanced surface treatments and electrically benign nature of common defects are responsible for the existing high performance and future promise in chalcopyrite-based photovoltaic devices. The presence a Cu-poor phase layer between the absorber and buffer layers in CIGS solar cells is known to enhance device performance, however, the overall properties and role of very thin layer remain poorly understood. Using first principles calculations based on density functional theory with screened hybrid functionals, we
explore the electronic structure and stability of a series ordered vacancy compounds (or OVCs) as a model for the Cu-poor phase layer. We calculate band offsets between the OVCs and defect-free chalcopyrite Cu and Ag based compounds (ABX2 where A = Cu, Ag; B = In, Ga, Al and X = S, Se). Using AB3X5 and AB5X8 stoichiometries as model OVC systems, we report on the variation of the band gap with A/B ratio and discuss the trends in other Cu and Ag-based chalcopyrites beyond CuInSe2. We find the valence and conduction bands are lower in energy in OVCs with respect to the parent ABX2 chalcopyrite owing to a reduced p-d interaction between X and A atoms. We additionally perform device-level simulations to assess the implications of the results, finding that the valence band offsets of OVCs are favorable for hole transport, while the conduction band offsets of chalcopyrites beyond CuInSe2-based absorbers may be detrimental in conventional solar cell device designs.
Abhsihek joined University of Delaware in 2014 as a graduate student in Department of Physics & Astronomy and started his PhD work with Prof. Anderson Janotti in 2015. He has received University of Delaware Doctoral Fellowship Award and a finalist for ‘Daicar-Bata best student research paper award’ in 2018. He was also awarded with ‘Ovshinsky student travel award’ for presenting contributed research talk by American Physical Society (APS) Division of Materials Physics at 2019 March meeting.