Tailored Band Structure of Cu(In,Ga)Se₂ Thin-Film Heterojunction Solar Cells: Depth Profiling of Defects and the Work Function

Abstract

An efficient carrier transport is essential for enhancing the performance of thin-film solar cells, in particular Cu­(In,Ga)­Se2 (CIGS) solar cells, because of their great sensitivities to not only the interface but also the film bulk. Conventional methods to investigate the outcoming carriers and their transport properties measure the current and voltage either under illumination or dark conditions. However, the evaluation of current and voltage changes along the cross-section of the devices presents several limitations. To mitigate this shortcoming, we prepared gently etched devices and analyzed their properties using micro-Raman scattering spectroscopy, Kelvin probe force microscopy, and photoluminescence measurements. The atomic distributions and microstructures of the devices were investigated, and the defect densities in the device bulk were determined via admittance spectroscopy. The effects of Ga grading on the charge transport at the CIGS–CdS interface were categorized into various types of band offsets, which were directly confirmed by our experiments. The results indicated that reducing open-circuit voltage loss is crucial for obtaining a higher power conversion efficiency. Although the large Ga grading in the CIGS absorber induced higher defect levels, it effectuated a smaller open-circuit voltage loss because of carrier transport enhancement at the absorber–buffer interface, resulting from the optimized conduction band offsets.

Advance Supply of Ag and Ga–Se for Increased Backside Ga and Enhanced Cu(In,Ga)Se2 Solar Cell Efficiency

“…This meticulous consideration of parameters helps maintain a high V OC in solar cells, leading to enhanced performance. 15,16 The results of this study provide conclusive evidence for enlarging the grain size in Ag-alloyed CIGS solar cells through a comprehensive analysis of the bandgap grading variations. Grain size is closely related to structural or electronic defects in most semiconductor materials.…”

Improving open-circuit voltage deficit by interface passivation via Li treatment in Cu2ZnSn(S,Se)4 solar cells

“…3(a)). 41 Raman spectroscopy was performed to investigate the phase distribution on This journal is © The Royal Society of Chemistry 2023 the ground surfaces. Raman spectra were obtained for seven points from the front side of CZTSSe to the Mo back contact.…”

Design Simulation of Chalcogenide Absorber‐Based Heterojunction Solar Cell Yielding Manifold Enhancement in Efficiency

“…This modification has a great influence on the absorption of radiation, recombination process, transport, and collection of photo-generated carriers. [28][29][30] Further, lowering in sulfur mole fraction in the SnS absorber reduces the conduction band minimum (CBM) and E g of the absorber layer. This reduction in CBM and E g modulates the energy band alignment.…”