Characteristics of Cu(In,Ga)Se₂Films Prepared by Atmospheric Pressure Selenization of Cu-In-Ga Precursors Using Ditert-Butylselenide as Se Source

Abstract

In this study, copper indium gallium diselenide [Cu(In,Ga)Se 2 ; CIGS] films were prepared by selenization of Cu-In-Ga metallic precursors using ditert-butylselenide (DTBSe) under atmospheric pressure. Based on the results of θ-to-2θ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), it was found that the films selenized at 300 or 400 • C for 60 min showed the presence of Kirkendall voids along with the XRD signitures of pure copper (Cu) and certain intermediate binary selenides, copper indium diselenide (CIS) and CIGS depending on temperature while only a single CIGS structure was detected in those films selenized at 500 or 600 • C for 60 min. A 5-temperature selenization process was found to enable the formation of CIGS structure with better crystalline quality and thickness uniformity. It is believed that intermediate binary and ternary selenides are formed sequentially with increasing completeness during low-temperature selenization stages of the 5-temperature selenization process. This enhances the subsequent formation of CIGS structure at high-temperature selenization stages of the 5-temperature selenization process with improved structural and morphological properties.Cu(In,Ga)Se 2 is a I-III-VI 2 chalcopyrite semiconductor that has attracted much attention as a promising absorber for photovoltaic devices. Meanwhile, most CIGS films were prepared by physical vapor deposition (PVD) 1 including co-evaporation technique and molecular beam epitaxy (MBE). 2 Other methods such as sputtering, selenization of precursors, 3 solvothermal method, 4 and metallorganic chemical vapor deposition (MOCVD) 5 have also been reported. For simplicity and large-area fabrication, the most common CIGS preparation technique relies on pre-deposition of Cu-In-Ga metallic precursor followed by selenization using Se vapor 6 or H 2 Se gas. 7 Although the selenization of Cu-In-Ga metallic precursor using H 2 Se gas is a convenient approach for large scale CIGS thin film solar cell fabrication, the high toxicity of H 2 Se is a critical issue of safety concern. Therefore, the use of Se vapor is considered as an alternative for the selenization of a CIGS film. However, during the selenization process, it is difficult to incorporate Ga into the CIS structure. Instead of forming a single CIGS quaternary phase, mixtures of CIS, CIGS, CGS or other secondary phases are often formed in the selenized films. Also, a selenization process using Se vapor needs to resort to a vacuum environment which is detrimental to the throughput of CIGS solar cell fabrication.Organoselenides including dimethylselenide [(CH 3 ) 2 Se:DMSe], 8 diethylselenide [(C 2 H 5 ) 2 Se:DESe], 3 and ditert-butylselenide [(C 4 H 9 ) 2 Se:DTBSe] 9 have recently been proposed as alternative choices for the Se source. These organoselenides are liquid at room temperature and are stored in stainless steel container so that they are much safer than H 2 Se which is commonly stored in a high pre...

Fabrication of a smooth, large-grained Cu(In,Ga)Se2 thin film using a Cu/(In,Ga)2Se3 stacked precursor at low temperature for CIGS solar cells

“…In addition, the adhesion of CIGS to Mo back-contact is poor because of stress built-up by volume expansion 9 and void formation at the CIGS/Mo interface by out diffusion of metal atoms from the Mo surface. 10,11 As alternative Se sources, Se pellets 12,13 or metal-organic sources 14 were used instead of H 2 Se gas, but the interface void problem could not be easily solved. To avoid void formation, CIGS targets that already contained Se was employed.…”

A highly efficient Cu(In,Ga)(S,Se)2 photocathode without a hetero-materials overlayer for solar-hydrogen production

“…Both showed almost identical XRD patterns in good agreement with the typical CIGSSe chalcopyrite structure (JCPDS 35–1102). Binary compounds such as InSe and CuSe were not observed in the XRD patterns 29 . The Fig.…”

Tailoring Photoelectrochemical Performance and Stability of Cu(In,Ga)Se2 Photocathode via TiO2-Coupled Buffer Layers

“…It is observed that several hundred nm-sized voids were formed near the bottom Mo/CIGS interface in an otherwise compact polycrystalline CIGS film. It has been suggested that the formation of the voids was due to the Kirkendall effect driven by the differences in the diffusivity of outward-diffusing indium, gallium, and/or copper, and that of sluggishly in-diffusing selenium during the low-temperature selenization. , However, the presence of the voids did not appear to seriously affect the operation of CIGS as a light-absorbing electrode, as confirmed by good device performance (photoconversion efficiency ∼14.7%) of solar cells based on a CIGS absorber prepared by the same batch (see Figure S2 in Supporting Information). A MoSe 2 layer with an average thickness of 40 nm was formed during the selenization, which has been known to create good ohmic contact to the CIGS and this should be beneficial for the PEC performances. , …”