Raman spectra of CuInSe2

Accelerating the Development of Thin Film Photovoltaic Technologies: An Artificial Intelligence Assisted Methodology Using Spectroscopic and Optoelectronic Techniques

Thin film photovoltaic (TFPV) materials and devices present a high complexity with multiscale, multilayer, and multielement structures and with complex fabrication procedures. To deal with this complexity, the evaluation of their physicochemical properties is critical for generating a model that proposes strategies for their development and optimization. However, this process is time-consuming and requires high expertise. In this context, the adoption of combinatorial analysis (CA) and artificial intelligence (AI) strategies represents a powerful asset for accelerating the development of these complex materials and devices. This work introduces a methodology to facilitate the adoption of AI and CA for the development of TFPV technologies. The methodology covers all the necessary steps from the synthesis of samples for CA to data acquisition, AI-assisted data analysis, and the extraction of relevant information for research acceleration. Each step provides details on the necessary concepts, requirements, and procedures and are illustrated with examples from the literature. Then, the application of the methodology to a complex set of samples from a TFPV production line highlights its ability to rapidly glean significant insights even in intricate scenarios. The proposed methodology can be applied to other types of materials and devices beyond PV and using different characterization techniques.

Wurtzite CuIn(SxSe1-x)2 Nanocrystals: Colloidal Synthesis and Band-Gap Engineering

CuIn(SxSe1-x)2 nanocrystals as an emerging class of functional materials present huge potential for industrial applications; however, the synthesis of CuIn(SxSe1-x)2 nanocrystals remains a formidable challenge in achieving both tunable band gap and phase. Here, we reported a facile hot-injection method for synthesizing a family of wurtzite CuIn(SxSe1-x)2 nanocrystals, enabling manipulation of the S and Se contents across the entire compositional range (0 ≤ x ≤ 1). The obtained nanocrystals exhibit band gaps ranging from 1.21 to 1.58 eV, which vary depending on the S/Se ratios in the products. This approach can be readily extended to other scenarios involving chalcogenide nanomaterials, thereby facilitating the advancement of next-generation functional materials and applications.

Fabrication of CZTSe/CIGS Nanowire Arrays by One-Step Electrodeposition for Solar-Cell Application

The paper reports some preliminary results concerning the manufacturing process of CuZnSnSe (CZTSe) and CuInGaSe (CIGS) nanowire arrays obtained by one-step electrodeposition for p-n junction fabrication. CZTSe nanowires were obtained through electrodeposition in a polycarbonate membrane by applying a rectangular pulsed current, while their morphology was optimized by appropriately setting the potential and the electrolyte composition. The electrochemical parameters, including pH and composition of the solution, were optimized to obtain a mechanically stable array of nanowires. The samples were characterized by scanning electron microscopy, Raman spectroscopy, and energy-dispersion spectroscopy. The nanostructures obtained showed a cylindrical shape with an average diameter of about 230 nm and a length of about 3 µm, and were interconnected due to the morphology of the polycarbonate membrane. To create the p-n junctions, first a thin film of CZTSe was electrodeposited to avoid direct contact between the ZnS and Mo. Subsequently, an annealing process was carried out at 500 °C in a S atmosphere for 40 min. The ZnS was obtained by chemical bath deposition at 95 °C for 90 min. Finally, to complete the cell, ZnO and ZnO:Al layers were deposited by magnetron-sputtering.

Gallium In-Depth Profile in Bromine- Etched Copper-Indium-Galium-(Di)selenide (CIGS) Thin Films Inspected Using Raman Spectroscopy

In the thin film solar cells domain, copper indium galium (di)selenide (CIGS) is a material with well-established photovoltaic purpose. Here the presence of a suitable [Ga]/([Ga]+[In]) (GGI) in-depth profile has proved to play a key role in the performance of cells. The implementation of a routine method based on reliable but easily available experimental techniques is mandatory to obtain information on the GGI profile of any CIGS layer, in order to achieve high efficiency chalcogenide layers. In this vein, we here propose and systematically test a simple method for the GGI profile determination based on repeated bromine etching of CIGS thin films followed by Raman analysis of the A₁ peak position. The reliability of the proposed approach is verified using a methodical comparison with energy-dispersive X-ray spectroscopy (EDS) analysis and secondary ion mass spectroscopy (SIMS) profiles, showing a good agreement with the GGI in-depth profiles determined using Raman analysis on bromine etched samples.

Orientation-distribution mapping of polycrystalline materials by Raman microspectroscopy

Raman microspectroscopy provides the means to obtain local orientations on polycrystalline materials at the submicrometer level. The present work demonstrates how orientation-distribution maps composed of Raman intensity distributions can be acquired on large areas of several hundreds of square micrometers. A polycrystalline CuInSe₂ thin film was used as a model system. The orientation distributions are evidenced by corresponding measurements using electron backscatter diffraction (EBSD) on the same identical specimen positions. The quantitative, local orientation information obtained by means of EBSD was used to calculate the theoretical Raman intensities for specific grain orientations, which agree well with the experimental values. The presented approach establishes new horizons for Raman microspectroscopy as a tool for quantitative, microstructural analysis at submicrometer resolution.

Aqueous Solution-Phase Selenized CuIn(S,Se)2 Thin Film Solar Cells Annealed under Inert Atmosphere

A nonvacuum solution-based approach can potentially be used to realize low cost, roll-to-roll fabrication of chalcopyrite CuIn(S,Se)2 (CISSe) thin film solar cells. However, most solution-based fabrication methods involve highly toxic solvents and inevitably require sulfurization and/or postselenization with hazardous H2S/H2Se gases. Herein, we introduce novel aqueous-based Cu-In-S and Se inks that contain an amine additive for producing a high-quality absorber layer. CISSe films were fabricated by simple deposition of Cu-In-S ink and Se ink followed by annealing under an inert atmosphere. Compositional and phase analyses confirmed that our simple aqueous ink-based method facilitated in-site selenization of the CIS layer. In addition, we investigated the molecular structures of our aqueous inks to determine how crystalline chalcopyrite absorber layers developed without sulfurization and/or postselenization. CISSe thin film solar cells annealed at 550 °C exhibited an efficiency of 4.55% under AM 1.5 illumination. The low-cost, nonvacuum method to deposit chalcopyrite absorber layers described here allows for safe and simple processing of thin film solar cells.

Crystalline photoactive copper indium diselenide thin films by pulsed laser crystallization of nanoparticle-inks at ambient conditions

Direct pulsed laser crystallization (DPLC) is explored to rapidly crystallize large area coated copper indium diselenide (CIS) nanoparticle-inks.

Effects of photo-assisted electrodeposited on CuInSe2 thin films

Photo-assisted one-step electrodeposition has been applied to help in forming smooth and dense CuInSe2 films. The difference in surface morphology and crystalline quality between CuInSe2 films with various photo-assistance has been investigated. In the photo-assisted electrodeposition process, the many kinds of lamps providing maximum light intensity at about 380 to 620 nm were used as light source to be irradiated onto the surface of Mo-coated soda-lime glass substrates. The results suggested effects of photo-assistance including activating surface diffusion and growing high-crystalline quality films with reduced defects during electrodeposition.

Colloidal solution-processed CuInSe2 solar cells with significantly improved efficiency up to 9% by morphological improvement

We demonstrate here that an improvement in the green density leads to a great enhancement in the photovoltaic performance of CuInSe2 (CISe) solar cells fabricated with Cu-In nanoparticle precursor films via colloidal solution deposition. Cold-isostatic pressing (CIP) increases the precursor film density by ca. 20%, which results in an appreciable improvement in the microstructural features of the sintered CISe film in terms of a lower porosity, a more uniform surface morphology, and a thinner MoSe2 layer. The low-band-gap (1.0 eV) CISe solar cells with the CIP-treated films exhibit greatly enhanced open-circuit voltage (V(OC), typically from 0.265 to 0.413 V) and fill factor (FF, typically from 0.34 to 0.55), compared to the control devices. As a consequence, an almost 3-fold increase in the average efficiency, from 3.0 to 8.2% (with the highest value of 9.02%), is realized. Diode analysis reveals that the enhanced V(OC) and FF are essentially attributed to the reduced reverse saturation current density and diode ideality factor. This is associated with suppressed recombination, likely due to the reduction in recombination sites at grain/air surfaces, intergranular interfaces, and defective CISe/CdS junctions. From the temperature dependences of V(OC), it is revealed that CIP-treated devices suffer less from interface recombination.

Template based precursor route for the synthesis of CuInSe2 nanorod arrays for potential solar cell applications

Polycrystalline CuInSe2 (CISe) nanorods are promising for the fabrication of highly efficient active layers in solar cells. In this work we report on a nanocasting approach, which uses track-etched polycarbonate films as hard templates for obtaining three-dimensionally (3D) arranged CISe nanorod arrays. Copper and indium ketoacidoximato complexes and selenourea were employed as molecular precursors. Arrays of parallel isolated cylindrical pores of 100 nm nominal diameter and 5 μm length were used for the infiltration of the precursor solution under inert atmosphere, followed by drying, thermal conversion into a preceramic 'green body', a subsequent dissolution of the template, and a final thermal treatment at 450 °C. The nanorods that where synthesised in this way have dimensions equal to the pore sizes of the template. Investigation of the CuInSe2 nanorod samples by spectroscopic and diffraction methods confirmed a high purity and crystallinity, and a stoichiometric composition of the CISe ternary semiconductor compound.

Solvothermal Preparation and Spectroscopic Characterization of Copper Indium Diselenide Nanorods

Single-crystalline chalcopyrite CuInSe(2) nanorods (CuInSe(2)NRs) of 50-100 nm in diameter and up to a few micrometers in length have been synthesized solvothermally. High-resolution transmission electron microscopic images of the CuInSe(2)NRs reveal the d-spacing of 0.335 nm for the (112) crystalline planes and a growth direction along [331]. The near-infrared absorption spectrum of the chalcopyrite CuInSe(2)NRs shows a peak maximum at 1162 nm and an onset at 1262 nm, indicating no apparent blue-shift compared with those of Cu-rich CuInSe(2) thin films. An intense peak at 175.1 cm(-1) in the room-temperature Raman scattering spectrum of CuInSe(2)NRs corresponds to the A(1) phonon mode of tetragonal CuInSe(2) chalcopyrite. The narrower full width at half-maximum (fwhm) of 9.5 cm(-1) for CuInSe(2)NRs, in comparison with fwhm approximately 12 cm(-1) for CuInSe(2) films, indicates a uniform size distribution and single crystallization in the nanorods. Analysis of the photoluminescence from the single-crystalline CuInSe(2)NRs measured at 10 K has categorized the emission into seven groups of transitions as characterized by free excitons, bound excitons, conduction band to acceptor levels, and bound excitons at different defects.