Sodium Passivation of the Grain Boundaries in CuInSe₂ and Cu₂ZnSnS₄ for High‐Efficiency Solar Cells

Abstract

It is well known that sodium at grain boundaries (GBs) increases the photovoltaic efficiencies of CuInSe 2 and Cu 2 ZnSnS 4 significantly. However, the mechanism of how sodium influences the GBs is still unknown. Based on the recently proposed self-passivation rule, it is found that the dangling bonds in the GBs can completely be saturated through doping the Na, thus GB states are successfully passivated. It is shown that the Na can easily incorporate into the GB with very low formation energy. Although Cu can also passivate the GB states, it requires a copper rich condition which, however, suppresses the formation of copper vacancies in the bulk and thus decreases the concentration of hole carriers, so copper passivation is practically not as beneficial as sodium. The present work reveals the mechanism about how the Na enhances the photovoltaic performance through passivating the dangling bonds in the GBs of chalcogenide semiconductors, and sheds light on how to passivate dangling bonds in GBs with alterative processes.

Prediction of Novel p‐Type Transparent Conductors in Layered Double Perovskites: A First‐Principles Study

“…As a quaternary compound, Cs 4 CdSb 2 Cl 12 could have more possible types of intrinsic point defects compared to ternary and binary compounds. For this reason, growing high quality Cs 4 CdSb 2 Cl 12 thin film is expected to be more challenging, similar to other quaternary compounds . As shown in Figure , the stoichiometric Cs 4 CdSb 2 Cl 12 can only be stabilized in a narrow area of chemical potentials to avoid the formation of any possible competitive secondary phases, similar to the cases of Cu 2 ZnSnS 4 and Cu 2 ZnSnSe 4 .…”

“…For this reason, growing high quality Cs 4 CdSb 2 Cl 12 thin film is expected to be more challenging, similar to other quaternary compounds . As shown in Figure , the stoichiometric Cs 4 CdSb 2 Cl 12 can only be stabilized in a narrow area of chemical potentials to avoid the formation of any possible competitive secondary phases, similar to the cases of Cu 2 ZnSnS 4 and Cu 2 ZnSnSe 4 . All the 20 intrinsic defects considered in Cs 4 CdSb 2 Cl 12 include four vacancies (V Cs , V Cd , V Sb , and V Cl ), four interstitials (Cs i , Cd i , Sb i , and Cl i ), six cation‐on‐cation antisites (Cs Sb , Cs Cd , Cd Cs , Cd Sb , Sb Cs , and Sb Cd ), three cation‐on‐anion antisites (Cs Cl , Cd Cl, and Sb Cl ) and three anion‐on‐cation antisites (Cl Cs , Cl Cd, and Cl Sb ).…”

Role of surface microstructure of Mo back contact on alkali atom diffusion and Ga grading in Cu(In,Ga)Se2 thin film solar cells

“…Alkali element plays a vital role in the development of CIGS solar cells as well as other solar cells like kesterite-based Cu 2 ZnSn(S,Se) 4 solar cells. [7][8][9][10] The importance of Na in the electrical performance of CIGS solar cells was first reported in 1993 by Hedstrom et al 11 Since then, many researchers have investigated the effects of alkali elements in different | 755 GONG et al…”

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.…”