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How band tail recombination influences the open‐circuit voltage of solar cells
Author(s) -
Wolter Max Hilaire,
Carron Romain,
Avancini Enrico,
Bissig Benjamin,
Weiss Thomas Paul,
Nishiwaki Shiro,
Feurer Thomas,
Buecheler Stephan,
Jackson Philip,
Witte Wolfram,
Siebentritt Susanne
Publication year - 2022
Publication title -
progress in photovoltaics: research and applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.286
H-Index - 131
eISSN - 1099-159X
pISSN - 1062-7995
DOI - 10.1002/pip.3449
Subject(s) - recombination , spontaneous emission , open circuit voltage , thermalisation , radiative transfer , band gap , solar cell , non radiative recombination , photoluminescence , physics , theory of solar cells , atomic physics , energy conversion efficiency , solar cell efficiency , optoelectronics , materials science , voltage , chemistry , optics , laser , biochemistry , quantum mechanics , gene
The power conversion efficiency of solar cells strongly depends on the open‐circuit voltage V OC which, in turn, depends on the recombination activity within the device. A possible source of detrimental charge carrier recombination is band tails. An empirical linear relationship between V OC loss and the Urbach energy of the band tails has been shown in the past. Here we discuss how band tails influence the radiative recombination and the nonradiative recombination in the bulk of the absorber. First, we show through photoluminescence that the band tails can be willfully tuned in state‐of‐the‐art thin‐film Cu (In,Ga)Se 2 (CIGSe) absorbers and solar cells on a 20% efficiency level and beyond through the incorporation of alkali atoms. In the second part, we compare our CIGSe results to published results from other solar cell technologies. This comparison reveals that CIGS solar cells follow the previously described empirical trend: an increase in the open‐circuit voltage with decreasing band tails. Finally, we model the influence of tail states on the radiative and nonradiative recombination losses: Radiative recombination is increased because carriers thermalize into the tail states and nonradiative recombination of free carriers in the bands is increased because of Shockley–Read–Hall recombination through the tail states. The comparison with experimental data shows that the influence of tail states is even worse than the increase in radiative and SRH recombination predicted by our model. Our results thus suggest that band tails act as one of the main remaining voltage limitations in the majority of state‐of‐the‐art solar cells.