Defect Engineering in Multinary Earth‐Abundant Chalcogenide Photovoltaic Materials

Abstract

IntroductionChalcogenide photovoltaic (PV) materials such as CdTe [1,2] and Cu(In,Ga)Se 2 (CIGSe) [3][4][5] have enabled remarkable progress in thin-film PV device performance, with each technology exceeding the 20% power conversion efficiency (PCE) barrier. However, two major concerns remain regarding these technologies-i.e., the negative environmental impacts of Cd Application of zinc-blende-related chalcogenide absorbers such as CdTe and Cu(In,Ga)Se 2 (CIGSe) has enabled remarkable advancement in laboratory-and commercial-scale thin-film photovoltaic performance; however concerns remain regarding the toxicity (CdTe) and scarcity (CIGSe/CdTe) of the constituent elements. Recently, kesterite-based Cu 2 ZnSn(S,Se) 4 (CZTSSe) materials have emerged as attractive non-toxic and earth-abundant absorber candidates. Despite the similarities between CZTSSe and CIGSe/CdTe, the record power conversion efficiency of CZTSSe solar cells (12.6%) remains significantly lower than that of CIGSe (22.6%) and CdTe (22.1%) devices, with the performance gap primarily being attributed to cationic disordering and associated band tailing. To capture the promise of kesterite-like materials as prospective "drop-in" earth-abundant replacements for closely-related CIGSe, current research has focused on several key directions to control disorder, including: (i) examination of the interaction between processing conditions and atomic site disorder, (ii) isoelectronic cation substitution to introduce ionic size mismatch, and (iii) structural diversification beyond the zinc-blendetype coordination environment. In this review, recent efforts targeting accurate identification and engineering of anti-site disorder in kesterite-based CZTSSe are considered. Lessons learned from CZTSSe are applied to other complex chalcogenide semiconductors, in an effort to develop promising pathways to avoid anti-site disordering and associated band tailing in future high-performance earth-abundant photovoltaic technologies.

Efficient (Cu1−xAgx)2ZnSn(S,Se)4 solar cells on flexible Mo foils

“…17 Theoretical calculation demonstrated that the radius of Ag + (1.14Å) is substantially larger than that of Cu + (0.74Å) or Zn 2+ (0.74Å). 15 And the formation energy of Ag Zn defect (at 0.2 eV above the valence band edge) is much larger than that of the Cu Zn defect (0.12 eV). 16 There are several experimental studies reported the positive effects of the substitution of Cu by Ag on rigid glass substrates.…”

“…These results are in accordance with previous reports. 15,19,20 The XRD patterns of some binary and ternary selenide, such as ZnSe, and Cu 2 SnSe 3 , are similar to that of CZTSSe, so it is difficult to identify the phase purity of CZTSSe lms just by XRD characterization. The Raman spectra can be used as an effective tool to differentiate these impurities.…”

Suppressed Deep Traps and Bandgap Fluctuations in Cu2CdSnS4 Solar Cells with ≈8% Efficiency

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postdeposition alkali treatment to improve heterojunction diode quality in Cu(In,Ga) Se 2 (CIGS) solar cells and chloride treatment to passivate grain boundaries in CdTe solar cells. [3] Although the dominant limiting factors for this low performance are a matter of considerable discussion, [4] the following observations are consistent among kesterite absorbers: i) a low photoluminescence quantum yield (PLQY) and a short chargecarrier lifetime, [5] ii) a high value of Urbach band tail energy (larger than 30 meV for S-rich kesterites) and lack of a steep absorption onset, [6,7] and iii) the presence of secondary phases. [2] However, kesterite-based solar cells, such as Cu 2 ZnSn(S,Se) 4 , which share many of the same characteristics of CIGS and CdTe, significantly lag behind, with a record power conversion efficiency (PCE) of 12.6%.

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Proposition of an Environment Friendly Triple Junction Solar Cell Based on Earth Abundant CBTSSe/CZTS/ACZTSe Materials

“…In order to predict the minimum efficiency of our proposed structure, we have used much less minority carrier life times (0.25-0.52 ns) than that of the reported values in literature (7.1-11 ns). [18,19,23] The detailed simulation procedure and the other electrical and optical parameters along with their references can be found in the Supporting Information.…”

“…As a result, current density falls significantly with the higher thickness of CZTS (Figure 2(a)) because of the reduced optical power absorption in the bottom cell. Thus, higher thickness of [19] 7 [18] 8.5 [17] 7 [16] Band gap (eV) 1.9 [14] 1.45 [18] 0.97 [17] 0.9 [16] Electron affinity (eV) 3.6 [19] 4.1 [24] 4.05 [17,25] 4.05 [13] Electron effective mass (m e /m o ) 0.37 [14,15] 0.18 [13,16] 0.08 [17] 0.07 [13,16] Hole effective mass (m p /m o ) 1.68 [14] 2 [13,16] 0.3 [17] 0.2 [13,16] Electron mobility (cm 2 V À1 s À1 ) 3 0 [26] 40 [21,24] 75 [23] 145 [13,21] Hole mobility (cm 2 V À1 s À1 ) 1 0 [27] 25 [21] 1 [17,23] 35 [13,21] Acceptor concentration (cm…”