The Effect of ALD-Zn(O,S) Buffer Layer on the Performance of CIGSSe Thin Film Solar Cells

Abstract

In this paper, we report the development of Cd-free buffers using atomic layer deposition (ALD) for Cu(In,Ga)(S,Se)2-based solar cells. The ALD process gives good control of thickness and the S/S +O ratio content of the films. The influence of the growth per cycle (GPC) and the S/(S+O) ratio, and the glass temperature of the atomic layer deposited Zn(O,S) buffer layers on the efficiency of the Cu(In,Ga)(S,Se)2 solar cells were investigated. We present the first results from our work on cadmium-free CIGS solar cells on substrates with an aperture area of 0.4 cm2. These Zn(O,S) layers were deposited by atomic layer deposition at 120 °C with S/Zn ratios of 0.7, and layers of around 30 nm. The Zn(O,S) 20% (Pulse Ratio: H2S/H2O+H2S) process results in a S/Zn ratio of 0.7. We achieved independently certified aperture area efficiencies of 17.1% for 0.4 cm2 cells.

Optical and Structural Characterization of Cd-Free Buffer Layers Fabricated by Chemical Bath Deposition

“…In general, most of the CIGS-based solar cells include a very thin CdS (<100 nm) as a buffer layer to reduce crystalline mismatch between the chalcopyrite absorber layer and the transparent ZnO front electrode [12,13]. In the last two decades, serious efforts have been made to replace the CdS buffer layer by other nontoxic Coatings 2021, 11, 897 2 of 12 material [14][15][16]. Actually, in their last report, Green et al reported an efficiency value of 23.3% for CIGS cells free of Cd [17].…”

“…Actually, in their last report, Green et al reported an efficiency value of 23.3% for CIGS cells free of Cd [17]. Different compounds have been reported as alternatives to fabricate Cd-free buffer layers (e.g., ZnS [18], Zn(O,S) [15], ZnSe [19], In 2 S 3 [20], CdS [21]). Among the semiconductor options, Zn(O,OH)S coatings are widely used as thin films in the fabrication of luminescent materials, light-emitting diodes, electroluminescent devices, optical covers, reflectors, and dielectric filters [22][23][24][25][26][27].…”

Mixed‐Anion Compounds: An Unexplored Playground for ALD Fabrication

“…Among the ALD‐fabricated oxysulfide thin films, zinc oxysulfide Zn(O,S) is the most frequently reported material. [ 31,190,195,196,198,199,222–224 ] It is a wide bandgap semiconductor, for which the electronic and optical properties are controlled by the oxygen/sulfur content. [ 31,195,197,222,225,226 ] This makes it a potential candidate for buffer layers in thin‐film photovoltaics.…”