【Device Papers】Band-offset engineering and optical optimization of Cd-free CIGS solar cells using a β-Ga₂O₃ buffer layer

      Researchers from National Institute of Technology Nagaland Dimapur have published a dissertation titled " Band-offset engineering and optical optimization of Cd-free CIGS solar cells using a β-Ga₂O₃ buffer layer " in Solar Energy.

Abstract

      Cadmium sulfide (CdS) remains the standard buffer layer in Cu(In,Ga)Se₂ (CIGS) solar cells; however, its toxicity and short-wavelength absorption motivate Cd-free alternatives. Although gallium oxide has been explored as a passivation layer, its role as a transport-controlling buffer in CIGS remains insufficiently quantified. Here, two-dimensional ATLAS TCAD simulations are used to examine β-Ga₂O₃ /CIGS heterojunctions with emphasis on conduction-band alignment and interfacial transport.

      Buffer thickness (10–100 nm), donor concentration (10¹⁶-5×10¹⁸cm^-3)，and electron affinity (3.2–4.0 eV) are varied independently. Large positive conduction-band spikes (ΔE_c ≥ 0.5eV) induce transport barriers and S-shaped J-V behavior, as confirmed by quasi-Fermi-level bending at the interface. Reducing the offset to a shallow spike (ΔE_c≈0.18eV at X≈4.0 eV) restores efficient electron extraction while preserving hole blocking. An optimal thickness of 10–20 nm and donor density near 10¹⁸ cm⁻³ minimize resistive losses.

      The optimized device achieves 20.38% efficiency (J_sc=34.82mA cm^-2，V_oc=0.664 V，FF=82.4 %) with improved short-wavelength response relative to CdS. These results define quantitative alignment criteria for implementing β-Ga₂O₃ as a Cd-free CIGS buffer.

DOI：

https://doi.org/10.1016/j.solener.2026.114881