Defects properties and vacancy diffusion in Cu₂MgSnS₄

Abstract

Cu2ZnSnS4 (CZTS) is a promising photovoltaic absorber material, however, efficiency is largely hindered by potential fluctuation and a band tailing problem due to the abundance of defect complexes and low formation energy of an intrinsic CuZn defect. Alternatives to CZTS by group I, II, or IV element replacement to circumvent this challenge has grown research interest. In this work, using a hybrid (HSE06) functional, we demonstrated the qualitative similarity of defect thermodynamics and electronic properties in Cu2MgSnS4 (CMTS) to CZTS. We show SnMg to be abundant when in Sn- and Cu-rich condition, which can be detrimental, while defect properties are largely similar to CZTS in Sn- and Cu-poor. Under Sn- and Cu-poor chemical potential, there is a general increase in formation energy in most defects except SnMg, CuMg remains as the main contribution to p-type carriers, and SnMg may be detrimental because of a deep defect level in the mid gap and the possibility of forming defect complex SnMg+MgSn. Vacancy diffusion is studied using generalized gradient approximation, and we find similar vacancy diffusion properties for Cu vacancy and lower diffusion barrier for Mg vacancy, which may reduce possible Cu-Mg disorder in CMTS. These findings further confirm the feasibility of CMTS as an alternative absorber material to CZTS and suggest the possibility for tuning defect properties of CZTS, which is crucial for high photovoltaic performance.

CZTSSe solar cells: insights into interface engineering

“…91,114 However, its application is limited due to its toxicity, generation of hazardous waste aer deposition, and low J SC due to parasitic losses in the short-wavelength range. 100,115 On the one hand, the conduction band offset between CdS and CZTSSe is an essential cause of the voltage decit, 116,117 while on the other hand, the lattice mismatch at the interface between CZTS and CdS is ∼7% (or for CIGS and CdS, it is ∼1.5%), 118,119 and high area density interface defects can therefore be anticipated at the CZTS/CdS interface, thus increasing interfacial Shockley-Read-Hall recombination and decreasing the VOC of the device. 119 In addition, the relatively low band gap of CdS (E g = 2.4-2.5 eV) leads to a signicant loss of light absorption, reducing the solar cells' J SC .…”