Abstract
Kesterite solar cells show the highest efficiency when the absorber layers (Cu ZnSnS [CZTS], Cu ZnSnSe [CZTSe] and their alloys) are non-stoichiometric with Cu / (Zn + Sn) ≈ 0.8 and Zn / Sn ≈ 1.2. The fundamental cause is so far not understood. Using a first-principles theory, we show that passivated defect clusters such as Cu + Sn and 2 Cu+ Sn have high concentrations even in stoichiometric samples with Cu/(ZnSn) and Zn/Sn ratios near 1. The partially passivated Cu+ Sn cluster produces a deep donor level in the band gap of CZTS, and the fully passivated 2Cu+ Sn cluster causes a significant band gap decrease. Both effects are detrimental to photovoltaic performance, so Zn-rich and Cu, Sn-poor conditions are required to prevent their formation and increase the efficiency. The donor level is relatively shallower in CZTSe than in CZTS, which gives an explanation to the higher efficiency obtained in Cu ZnSn (S, Se) (CZTSSe) cells with high Se content.
| Original language | English |
|---|---|
| Article number | 223901 |
| Journal | Applied Physics Letters |
| Volume | 101 |
| Issue number | 22 |
| DOIs | |
| Publication status | Published - 26 Nov 2012 |
Access to Document
- ApplPhysLett 101 223901
Copyright 2012 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in: Chen, S., Wang, L-W., Walsh, A., Gong, X. G., & Wei, S-H. (2012). Abundance of CuZn + SnZn and 2CuZn + SnZn defect clusters in kesterite solar cells. Applied Physics Letters, 101(22), 223901, and may be found at http://dx.doi.org/10.1063/1.4768215