Premium
Cu–Zn disorder and band gap fluctuations in Cu 2 ZnSn(S,Se) 4 : Theoretical and experimental investigations
Author(s) -
Scragg Jonathan J. S.,
Larsen Jes K.,
Kumar Mukesh,
Persson Clas,
Sendler Jan,
Siebentritt Susanne,
Platzer Björkman Charlotte
Publication year - 2016
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.201552530
Subject(s) - czts , passivation , band gap , raman spectroscopy , materials science , photoluminescence , solar cell , condensed matter physics , zinc , ab initio , wide bandgap semiconductor , analytical chemistry (journal) , optoelectronics , chemistry , nanotechnology , physics , optics , metallurgy , layer (electronics) , organic chemistry , chromatography
Cu 2 ZnSn(S,Se) 4 (CZTS(e)) solar cells suffer from low‐open‐circuit voltages that have been blamed on the existence of band gap fluctuations, with different possible origins. In this paper, we show from both theoretical and experimental standpoints that disorder of Cu and Zn atoms is in all probability the primary cause of these fluctuations. First, quantification of Cu–Zn disorder in CZTS thin films is presented. The results indicate that disorder is prevalent in the majority of practical samples used for solar cells. Then, ab initio calculations for different arrangements and densities of disorder‐induced [Cu Zn + Zn Cu ] defect pairs are presented and it is shown that spatial variations in band gap of the order of 200 meV can easily be caused by Cu–Zn disorder, which would cause large voltage losses in solar cells. Experiments using Raman spectroscopy and room temperature photoluminescence combined with in situ heat‐treatments show that a shift in the energy of the dominant band‐to‐band recombination pathway correlates perfectly to the order‐disorder transition, which clearly implicates Cu–Zn disorder as the cause of band gap fluctuations in CZTS. Our results suggest that elimination or passivation of Cu–Zn disorder could be very important for future improvements in the efficiency of CZTS(e)‐based solar cells.