Three-step H2Se/Ar/H2S reaction of Cu-In-Ga precursors for controlled composition and adhesion of Cu(In,Ga)(Se,S)2 thin films

Abstract

Control of the through-film composition and adhesion are critical issues for Cu(In,Ga)Se2 (CIGS) and/or Cu(In,Ga)(Se,S)2 (CIGSS) films formed by the reaction of Cu–In–Ga metal precursor films in H2Se or H2S. In this work, CIGSS films with homogenous Ga distribution and good adhesion were formed using a three-step reaction involving: (1) selenization in H2Se at 400 °C for 60 min, (2) temperature ramp-up to 550 °C and annealing in Ar for 20 min, and (3) sulfization in H2S at 550 °C for 10 min. The 1st selenization step led to fine grain microstructure with Ga accumulation near the Mo back contact, primarily in a Cu9(In1−xGax)4 phase. The 2nd Ar anneal step produces significant grain growth with homogenous through-film Ga distribution and the formation of an InSe binary compound near the Mo back contact. The 3rd sulfization step did not result in any additional change in Ga distribution or film microstructure but a small S incorporation near the CIGSS film surface and complete reaction of InSe to form CIGSS were observed. The three-step process facilitates good control of the film properties by separating different effects of the reaction process and a film growth model is proposed. Finally, CIGSS solar cells with the three-step reaction were fabricated and devices with efficiency = 14.2% and VOC = 599 mV were obtained.

12.4% Efficient Cu(In,Ga)Se2 solar cell prepared from one step electrodeposited Cu–In–Ga oxide precursor layer

“…Another option may be the substitution of selenium by sulfur at the surface which would result in the same band gap opening. This is achieved successfully with multi-step selenization/sulfuration processes [25,26]. This approach could also be applied in the present case.…”

Improvement of Pre-Annealed Cu(In, Ga)Se<SUB>2</SUB> Absorbers for High Efficiency

“…We similarly obtained the V OC of the solar cells, which we explain by the band gap values due to Ga accumulation that the pre-annealing process was not able to solve. 12 Even if the V OC of the solar cells were similar, the resulting J SC of the pre-annealed solar cell was higher, except below 550 nm and beyond 1100 nm, so that the pre-annealed solar cell had a higher quantum efficiency to obtain a better J SC , due to the pre-annealing role previously mentioned. The pre-annealed solar cell reached the highest conversion efficiency of 8.44% in this experiment.…”

Distinction of [220] and [204] textures of Cu(In,Ga)Se2 film and their growth behaviors depending on substrate nature and Na incorporation

“…Among various deposition techniques of CIGS film [23][24][25][26], we prepared a 2.0 μm-thick CIGS film via a well-known and widely-used multistage process in a sequence of In-Ga-Se/Cu-Se/In-Ga-Se deposition [27]. Using this CIGS absorber, the solar cell shows a PCE of 16.4% in a structure of Al/Ni/ITO/ZnO/CdS/CIGS/Mo/soda-lime glass (SLG) without anti-reflection coating [28].…”