Size and grain-boundary effects on the performance of polycrystalline CIGS-based solar cells

Abstract

This work reviews the effect of Geometrical, physical and electrical parameters of the polycristalline CIGS thin film used as absorber materials in substrate CuIn 0.7 Ga 0.3 Se 2 (CIGS) solar cells. Two-dimensional device simulator Atlas SILVACO-TCAD was employed to study the performances of ZnO:Al/CdS/CIGS/Metal solar cell structure. The impacts of the grain sizes and the grain boundaries (GBs) in the polycrystalline p-CIGS absorber layer have been investigated. The variation of grain sizes in the CIGS bulk was studied and the corresponding design optimization was provided. The best energy conversion efficiencies have been obtained with large grain sizes higher than 2 μm for 3 μm-CIGS thick. The simulation results predict a strong detrimental effect of GBs recombination, which is enhanced by the presence of small width in the direction that attracts minority carriers. An efficiency of 17.1% (with V oc 0.68 V, J sc 34 mA/cm 2 and FF 0.77) has been achieved with small width at about 3 nm. The presence of the valence-band offset in the absorber layer is benign to solar cell performance by limit the carriers recombination. The valence-band offset is predicted to be 0.4 eV in magnitude and localized to a very thin layer at the grain surface in which the surface reconstruction takes place. All these simulation results give some important indication to lead a higher efficiency of polycrystalline CIGS solar cells for feasible fabrication.

Review—Solution Processing of CIGSe Solar Cells Using Simple Thiol-Amine Solvents Mixture: A Review

“…[46][47][48] The process also enlarges grain size, which effectively decreases grain boundary concentration, potentially boosts carrier mobility, reduces the chance of electron-hole recombination, and subsequently increases current generation. [49][50][51] The next section discusses the development of a molecular-based approach for CIGSe PV devices using the thiol-amine solvent combination. Table I summarizes the recent PV performance of processed CIGSe thin-film devices fabricated using the thiol-amine route.…”

Characterization and simulation of CIGS thin-film solar cells and interconnects

“…This was suggested to be due to the formation of different defects in grain boundaries, both donor and acceptor type that create a potential well in the band structure, though the width of these wells was found to be around 1-2 nm. Grain boundaries were also studied with simulation tools, such as in [Idris, 2015], in which a CIGS solar cell with a grain boundary is simulated. Different properties related to the grain boundary, such as the width of the grain or the width of the grain boundary were varied, and it was found that larger grain sizes correlate with increased efficiencies while larger grain boundary widths are related to lower efficiencies [Idris, 2015].…”

“…Grain boundaries were also studied with simulation tools, such as in [Idris, 2015], in which a CIGS solar cell with a grain boundary is simulated. Different properties related to the grain boundary, such as the width of the grain or the width of the grain boundary were varied, and it was found that larger grain sizes correlate with increased efficiencies while larger grain boundary widths are related to lower efficiencies [Idris, 2015].…”