@article{10902/29133,
year = {2021},
month = {2},
url = {https://hdl.handle.net/10902/29133},
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.},
organization = {Y.-H.C. Chang thanks the Ministry of Education of Taiwan for her Ph.D. scholarship, and Dr. Michael Sachs for fruitful discussions on TA data. J.R.D. would like to thank the UKRI Global Challenge Research Fund project SUNRISE (EP/P032591/1). L.S. acknowledges funding from the European Research Council (H2020-MSCA-IF-2016, Grant No. 749231). This work received financial support from the Swiss State Secretary for Education, Research and Innovation (SERI) under contract number 17.00105 (EMPIR project HyMet). The EMPIR programme is co-financed by the Participating States and by the European Union’s Horizon 2020 research and innovation programme.},
publisher = {Wiley-Blackwell},
publisher = {Advanced Energy Materials, 2021, 11(8), 2003446},
title = {Insights from transient absorption spectroscopy into electron dynamics along the Ga-gradient in Cu(In,Ga)Se2 solar cells},
author = {Chang, Yu-Han and Carron, Romain and Ochoa Gómez, Mario and Bozal Ginesta, Carlota and Tiwari, Ayodhya Nath and Durrant, James Robert and Steier, Ludmilla},
}