Nicolas Barreau

Cu(In,Ga)S₂ with a bandgap around 1.6–1.7 eV is a promising absorber for single‐junction and tandem solar cells, but its optical constants are poorly known because surface roughness, compositional gradients, and interfacial MoS₂ hinder reliable ellipsometry measurements. Here, we transfer bromide-based treatments developed for Se-based Cu(In,Ga)Se₂ to S-based Cu(In,Ga)S₂ to reduce the roughness and enable specular optical characterization. Using a CuPRO co-evaporation process with constant Ga/In flux, combined with a peel-off strategy to separately characterize Mo, MoS₂/Mo, and polished CIGS/MoS₂/Mo stacks, we extract the complex refractive index of 1.62 eV bandgap CIGS over 250 - 1800 nm. Implementing these optical constants in e-ARC simulations reproduces the EQE of the CdS/CIGS/Mo devices, for a photocurrent collection length of about 800 nm. We show that, despite a short collection length, the sharp absorption onset of wide-bandgap CIGS enables competitive photocurrents, and we recommend the extracted n,k data set for future optical design and current-matching studies of CIGS/Si and CIGS/CIGSe tandem solar cells.

This study investigates the optoelectronic characteristics of solar cells based on wide bandgap Cu(In,Ga)S ₂ (CIGS) absorbers, co‐evaporated onto glass substrates covered with 100 nm‐thick indium tin oxide (ITO) back contact. Devices based on absorbers with different thicknesses (ranging from 320 to 1580 nm) were investigated. Structural characterizations confirmed that all of the films were made of large grains, crystallized in the chalcopyrite structure with no secondary phases. It has been observed that the performance of the cells with front‐side illumination improves with increasing CIGS thickness, mainly because of increased short‐circuit current ( J _SC ). In contrast, the opposite trend is observed for rear‐side illumination, further suggesting a hindered collection of carriers generated close to the ITO/CIGS interface. The modelling of quantum efficiency using e‐ARC tool and Gartner theory suggests that all absorbers, independently of their thickness, are nearly fully depleted. In addition, they all exhibit a region with a low collection of photogenerated carriers at the vicinity of the ITO/CIGS interface. It is proposed that this area results from the consumption of gallium during gallium oxide formation at the ITO/CIGS interface.

We investigate the effect of post-deposition annealing on the defect-controlled electronic response of CdIn2S4 thin films using photocurrent-light-intensity analysis and transient photoconductivity. Relative to our previous annealing study, the present work extracts characteristic energy scales of the effective sub-bandgap states sampled under illumination and relates them to annealing-induced Fermi-level shifts. The measured Lux-Ampere characteristics evolve systematically from linear to sublinear behavior and, within the Rose and Bube formalisms, are consistent with reorganization of inversion-related antisite states and sulfur-vacancy-related defects. In the as-grown and vacuum-annealed films, the results support a distributed contribution of E states. Because the accessible energy window is limited by illumination range and Fermi-level position, the reconstructed profiles are interpreted as effective rather than absolute state distributions. These results refine the defect-state model of CdIn2S4 and clarify how annealing modifies trapping and recombination pathways.

Single-phase lamellar CIGS 5 (Cu 0.65 In 1.75 Ga 1.4 S 5, nominal composition) thin films were synthesized using co-evaporation. Structural, morphological and optoelectronic properties of these films have been investigated. The optical bandgap was calculated at approximately 2.1 eV, but extended band tails hinder an accurate determination. Such behavior may be related to the high density of point defects inherent in the crystal structure of CIGS5, which exhibits intrinsic cationic vacancies and mixed site occupancy. This results in compensated semiconducting behavior, with no clearly identified charge carriers. Nevertheless, photoelectrochemical measurements suggests an extremely weak excess of electron. Diverse solar cell architectures with CIGS 5 as absorber were fabricated. All exhibit very low efficiency. These poor performances are discussed and are attributed to the intrinsic optoelectronic properties of CIGS 5 material in ambient conditions due to a charge compensating effect.

A Cu(In,Ga)S ₂ -based hybrid photocathode protected by a protective layer and functionalized by a Co molecular complexes reduces CO ₂ in water with high rate and selectivity.

Chalcogenide‐based thin‐film solar cell optimized for rear illumination and used for CO₂ reduction is presented. Central to this innovation is a thinner, Cu(In,Ga)S₂ chalcopyrite absorber coated with a robust metallic top layer, which potentially surpasses the performance of conventional front‐illuminated designs. Using cobalt quaterpyridine molecular catalyst, photocurrent densities for CO₂ reduction exceeding 10 mA/cm² at 0.0 V vs. RHE under 1 Sun illumination, and ca. 16 mA/cm² at −0.25 V vs. RHE were achieved in voltammetry experiments. Controlled potential electrolysis showed catalytic activity over 20 h with selectivity for CO ranging from >92 % (first 4 hours) to 86 % at the end of the experiment. This approach opens limitless possibilities for employing various reduction catalysts, extending far beyond CO₂ reduction. It imposes minimal constraints on absorption properties, immobilization methods, and catalyst nature, setting the stage for high‐performance, adaptable PEC devices.