Abundance of Cu-Zn Sn-Zn and 2Cu(Zn) Sn-Zn defect clusters in kesterite solar cells

作者：Chen, Shiyou^*; Wang, Lin Wang; Walsh, Aron; Gong, X G; Wei, Su Huai

来源：Applied Physics Letters, 2012, 101(22): 223901.

DOI：10.1063/1.4768215

• Absorber layers
• Deep donor
• Defect cluster
• Donor levels
• First-principles theory
• Higher efficiency
• Non-stoichiometric
• Photovoltaic performance

Kesterite solar cells show the highest efficiency when the absorber layers (Cu2ZnSnS4 [CZTS], Cu2ZnSnSe4 [CZTSe] and their alloys) are non-stoichiometric with Cu/(Zn Sn) approximate to 0: 8 and Zn/Sn approximate to 1: 2. The fundamental cause is so far not understood. Using a first-principles theory, we show that passivated defect clusters such as Cu-Zn Sn-Zn and 2Cu(Zn) Sn-Zn have high concentrations even in stoichiometric samples with Cu/(Zn Sn) and Zn/Sn ratios near 1. The partially passivated Cu-Zn Sn-Zn cluster produces a deep donor level in the band gap of CZTS, and the fully passivated 2Cu(Zn) Sn-Zn 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 Cu2ZnSn(S, Se)(4) (CZTSSe) cells with high Se content.

• 出版日期2012-11-26
• 单位华东师范大学; 复旦大学