Guidelines for Optimization of the Absorber Layer Energy Gap for High Efficiency Cu(In,Ga)Se<sub>2</sub> Solar Cells

Abstract

This work investigates in-depth the effects of variation of the compositional ratio of the absorber layer in Cu(In,Ga)Se 2 (CIGS) thin-film solar cells. Electrical simulations were carried out in order to propose the most suitable gallium double-grading profile for the high efficiency devices. To keep the model as close as possible to the real behavior of the thin film solar cell a trap model was implemented to describe the bulk defects in the absorber layer. The performance of a solar cell with a standard CIGS layer thickness (2 μm) exhibits a strong dependence on the front grading height (decreasing band gap toward the middle of the CIGS layer). An absolute gain in the efficiency (higher than 1%) is observed by a front grading height of 0.22. Moreover, simulation results show that the position of the plateau (the region characterized by the minimum band gap) should be accurately positioned at a compositional ratio of 20% Ga and 80% In, which corresponds to the region where a lower bulk defect density is expected. The developed model demonstrates that the length of the plateau is not playing a relevant role, causing just a slight change in the solar cell performances. Devices with different absorber layer thicknesses were simulated. The highest efficiency is obtained for a CIGS thin film with thicknesses between 0.8 and 1.1 μm.

A Numerical Investigation on the Combined Effects of MoSe2 Interface Layer and Graded Bandgap Absorber in CIGS Thin Film Solar Cells

“…The optimum bandgap grading profile was found by simulating different values for these related bandgap grading parameters as presented in Table 2, and analyzing the corresponding J SC , V OC , FF, and PCE. Previous work by [34] shows that both grading parameters; i.e., the position of the notch and grading height (based on GGI) are equally significant to improve the cell performance through bandgap grading, hence the reason why these parameters were varied in this section. In order to accentuate the effects of bandgap grading, material parameters employed in the simulations were all kept unchanged except for the Ga composition dependent parameters such as bandgap energy, electron affinity, and optical absorption [17].…”

Optimizing the structure and optoelectronic properties of cuprite thin films via a plasma focus device as a solar cell absorber layer

“…[12][13][14] Characterized as a p-type semiconductor, Cu 2 O, with a direct bandgap ranging from 2.0 to 2.4 eV, 15 aptly suits its role as an absorber layer in solar cells. 16 The efficacy of Cu 2 O-based solar cells is contingent upon many factors, including the quality of the Cu 2 O thin films, 17 the positioning of the band at the interface between Cu 2 O and adjacent layers, 18 and the overall architecture of the device. 19 Consequently, the deposition of high-quality Cu 2 O thin films is paramount to developing proficient Cu 2 O-based solar cells.…”

“…12–14 Characterized as a p-type semiconductor, Cu 2 O, with a direct bandgap ranging from 2.0 to 2.4 eV, 15 aptly suits its role as an absorber layer in solar cells. 16…”