Engineering Grain Boundaries in Cu₂ZnSnSe₄ for Better Cell Performance: A First‐Principle Study

Abstract

Through first‐principle density functional theory (DFT) calculations, the atomic structure and electronic properties of intrinsic and passivated Σ3 (114) grain boundaries (GBs) in Cu2ZnSnSe4 (CZTSe) are studied. Intrinsic GBs in CZTSe create localized deep states within the band gap and thus act as Shockley‐Read‐Hall recombination centers, which are detrimental to cell performance. Defects, such as ZnSn (Zn atoms on Sn sites), Na+i (interstitial Na ions), and OSe (O atoms on Se sites), prefer to segregate into GBs in CZTSe. The segregation of these defects at GBs exhibit two beneficial effects: 1) eliminating the deep gap states via wrong bonds breaking or weakening at GBs, making GBs electrically benign; and 2) creating hole barriers and electron sinkers, promoting effective charge separation at GBs. The results suggest a unique chemical approach for engineering GBs in CZTSe to achieve improved cell performance.

Origin of High Electronic Quality in Structurally Disordered CH3NH3PbI3 and the Passivation Effect of Cl and O at Grain Boundaries

“…So far, no atomic structure of MAPbI 3 GBs has been reported in experiment. Previous investigation has shown that the electronic structures of GBs in conventional thin-fi lm solar cells [ 44,45 ] such as CdTe, CuInSe 2 , and Cu 2 ZnSnSe 4 are dominated by the anion-anion and/or cation-cation wrong bonds at the GB plane. For MAPbI 3 , we chose Σ3(111) GB and Σ5(310) GB as shown in Figure 2 for study because these two GBs include those wrong bonds.…”

“…Both theoretical and experimental observations suggest that Cl is unlikely in the MAPbI 3 bulk. Here, we examined the possibility of Cl at GBs because defect segregation at GBs is the usual phenomenon [ 44,45,[47][48][49] in thin-fi lm solar cells such as CdTe, CuInSe 2 , and Cu 2 ZnSnSe 4 . We found that in Σ5(310) GB, the total energies of Cl I at I-I wrong bond sites are about 0.2 eV lower than that in bulk, as shown in Figure 6 b, indicating that Cl can spontaneously segregate into the GB region.…”

Self-passivation rule and structure of CdTe Σ3 (112) grain boundaries

“…Obviously, the atomic configuration of prototype CSL Σ3 (112) GBs, without carefully accounting for bond rearrangement, is questionable. Similar Σ3 (112) GB models were also used in the study of Σ3 (114) GBs of ternary CuInSe2, 18 Σ3 (114) GBs of quaternary Cu2ZnSnSe4 19 and Σ5 (310) GBs of perovskite CH3NH3PbI3. 20 Therefore, a careful investigation of the possible atomic configurations of Σ3 (114) GBs and their properties is urgently needed and of general importance.…”

Opposing effects of stacking faults and antisite domain boundaries on the conduction band edge in kesterite quaternary semiconductors

“…Since current thin-film technologies mostly rely on polycrystalline materials, physical properties of extended defects, especially grain boundaries (GBs) have been investigated to understand their effects on the device efficiency [10][11][12][13][14][15][16]. Other extended defects like stacking faults (SFs) and antisite domain boundaries (ADBs) have been less documented as compared to the GBs, but since SFs in CdTe act as electron barriers and reduce the efficiency [17][18][19][20], SFs in CZTS should be investigated.…”