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Insights from transient absorption spectroscopy into electron dynamics along the Ga-gradient in Cu(In,Ga)Se2 solar cells

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Title: Insights from transient absorption spectroscopy into electron dynamics along the Ga-gradient in Cu(In,Ga)Se2 solar cells
Authors: Chang, Y-H
Carron, R
Ochoa, M
Bozal-Ginesta, C
Tiwari, AN
Durrant, J
Steier, L
Item Type: Journal Article
Abstract: Cu(In,Ga)Se2 solar cells have markedly increased their efficiency over the last decades currently reaching a record power conversion efficiency of 23.3%. Key aspects to this efficiency progress are the engineered bandgap gradient profile across the absorber depth, along with controlled incorporation of alkali atoms via post‐deposition treatments. Whereas the impact of these treatments on the carrier lifetime has been extensively studied in ungraded Cu(In,Ga)Se2 films, the role of the Ga‐gradient on carrier mobility has been less explored. Here, transient absorption spectroscopy (TAS) is utilized to investigate the impact of the Ga‐gradient profile on charge carrier dynamics. Minority carriers excited in large Cu(In,Ga)Se2 grains with a [Ga]/([Ga]+[In]) ratio between 0.2–0.5 are found to drift‐diffuse across ≈1/3 of the absorber layer to the engineered bandgap minimum within 2 ns, which corresponds to a mobility range of 8.7–58.9 cm2 V−1 s−1. In addition, the recombination times strongly depend on the Ga‐content, ranging from 19.1 ns in the energy minimum to 85 ps in the high Ga‐content region near the Mo‐back contact. An analytical model, as well as drift‐diffusion numerical simulations, fully decouple carrier transport and recombination behaviour in this complex composition‐graded absorber structure, demonstrating the potential of TAS.
Issue Date: 24-Feb-2021
Date of Acceptance: 29-Dec-2020
URI: http://hdl.handle.net/10044/1/86447
DOI: 10.1002/aenm.202003446
ISSN: 1614-6832
Publisher: Wiley-VCH Verlag
Journal / Book Title: Advanced Energy Materials
Volume: 11
Issue: 8
Copyright Statement: © 2021 The Authors. Advanced Energy Materials published by Wiley‐VCH GmbH This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Sponsor/Funder: Engineering and Physical Sciences Research Council
Commission of the European Communities
Funder's Grant Number: EP/P032591/1
Keywords: Science & Technology
Physical Sciences
Chemistry, Physical
Energy & Fuels
Materials Science, Multidisciplinary
Physics, Applied
Physics, Condensed Matter
Materials Science
charge carrier recombination
CIGS solar cells
composition gradient
minority carrier mobility
transient absorption spectroscopy
0303 Macromolecular and Materials Chemistry
0912 Materials Engineering
0915 Interdisciplinary Engineering
Publication Status: Published
Article Number: ARTN 2003446
Online Publication Date: 2021-01-14
Appears in Collections:Materials
Faculty of Natural Sciences

This item is licensed under a Creative Commons License Creative Commons