Cu(In,Ga)Se2 Research Articles

Investigation on thermal annealing effect on the physical properties of CuO-SnO2:F sprayed thin films for NO2 gas sensor and solar cell simulation

Thin films, owing to their versatility, are extensively employed in various applications, including solar cells and gas detection. In this study, CuO-SnO2:F thin films were fabricated using spray method. The influence of annealing temperature on their properties was examined. X-ray diffraction analysis of post-annealing at 300 °C revealed the emergence of the Cu2O phase, which disappeared at higher annealing temperatures of 500 °C. Substantial improvements in structural, optical, and electrical characteristics were observed, with the optimized films exhibiting heightened responsiveness at low NO2 gas concentration (4 ppm). The optimum operating temperature was determined at 150 °C, demonstrating small response and recovery times, and good reproducibility. Furthermore, Silvaco TCAD simulation was employed to model CIGS (Copper Indium Gallium Selenide) solar cells incorporating CuO-SnO2:F thin films as a buffer layer, yielding an impressive efficiency of 15.31 %.

CIGS bifacial solar cells with novel rear architectures: Simulation point of view and the creation of a digital twin

The performance of bifacial Cu(In,Ga)Se2 (CIGS) cells does not yet reach the one of monofacial cells, with standard Mo rear contacts. By exploring optoelectronic simulations, this study addresses the impact of a transparent conducting oxide layer used as rear contact in CIGS solar cells. These simulations, which aim to create a digital twin of bifacial CIGS solar cells, offer insight into the impact of novel rear contact architectures. It was observed that with an indium tin oxide (ITO) rear contact the CIGS cell performance lacks in comparison to a Mo one due to an electrical barrier, under rear side illumination these devices may only reach 3.9 % in conversion efficiency. The implementation of dielectric rear passivation schemes have great performance benefits in cells with Mo rear contacts. Therefore, the same passivation strategy in ITO contacts is discussed and additional novel architectures are proposed, from which a design of alternated lines between dielectric and 15 nm Mo layers on ITO showed promising results. Such rear architectures aim to achieve i) a highly transparent rear contact, ii) an ohmic-like behaviour with CIGS, and iii) a low defective interface with rear passivation. The selenization of the complete 15 nm Mo in the proposed novel architecture during the CIGS growth was considered, resulting in transmittance values above 70 % and, notably, reaching the transparency of bare ITO in the infrared range. Such rear architecture may provide for bifacial CIGS solar cells with conversion efficiency values surpassing 20 and 15 % for front and rear side illumination, respectively, allowing to fully exploit bifaciality.

Organic Electronics in Flexible Devices: Engineering Strategy, Synthesis, And Application

As global temperatures rise and fossil fuel reserves dwindle, the urgency to transition to renewable energy sources becomes paramount. Concentrated solar technology (CSP) together with technological advances in solar panels, especially the development of flexible solar cells, Is the key to solving these global challenges. This paper reviews the evolution of solar technology, highlighting the transition from traditional rigid panels to innovative thin-film photovoltaics such as cadmium telluride (CdTe), amorphous silicon, copper indium gallium selenide (CIGS), organic polymers, and perovskite solar cells. It delves into the engineering innovations that have propelled the field forward, including printing technologies and roll-to-roll processing, and explores the burgeoning applications of flexible solar cells in wearable electronics and building-integrated photovoltaics (BIPV). The discussion extends to the potential of emerging materials and technologies to enhance efficiency, stability, and environmental sustainability. Through a comprehensive analysis, this paper underscores the pivotal role of flexible solar cells in achieving a renewable energy future, emphasizing the need for continued research and development to overcome current limitations and fully realize their transformative potential.

The CIGS semiconductor detector for particle physics

Silicon is commonly used as a sensor material in a wide variety of imaging application.In recent high-energy and intensity beam experiments, high radiation tolerance is required, and new semiconductor detector consisting of radiation-hard materials have been investigated.The Cu(In,Ga)Se2 (CIGS) semiconductor is expected to possess high radiation tolerance, with the ability to recover from radiation damage through the compensation of defects by ions.The CIGS has originally developed for a solar cell and its radiation tolerance was investigated for the usage in space.The CIGS, featuring a recovery capability, would shed new light to particle detecror in high radiation environments.CIGS detectors (2 and 5 μm thick) were tested by Xe ion (400 MeV/u, 132Xe54+) at HIMAC, successfully detecting single Xe ion with a fast response.The output charge is understandable through estimation with the GEANT4 simulation.With 0.6 MGy irradiation by Xe ions, the CIGS output degraded to 50%, but it was recovered to 97% after the heat treatment under 130°C for 2 hours.This marks a significant step in confirming that CIGS semiconductors can serve as particle detectors with recovery features for radiation damage.

Review on the developments in copper indium gallium diselenide (CIGSe)-based thin film photovoltaic devices

Review on the developments in copper indium gallium diselenide (CIGSe)-based thin film photovoltaic devices

Photonic Crystal-Integrated Semitransparent Solar Cell for Solar Greenhouse Application

Solar greenhouse technology emerges as a solution that intensifies crop yields and allows utilities to generate energy from photovoltaic cells. Here, we demonstrate a photonic crystal-integrated solar cell that selectively transmits photosynthetic light for plant cultivation and reflects the remaining light to the adjacent solar cells to generate electricity. The photonic crystal is fabricated using an e-beam evaporation method by nonperiodic stacking of TiO2 and SiO2 layers to transmit light at 400–500 nm (blue) and 600–700 nm (red) and reflect green (500–600 nm), ultraviolet, and infrared light. The photonic crystal-integrated solar cell is constructed with the vertically arranged copper indium gallium diselenide (CIGS) solar cell and the tilted photonic crystal with respect to the CIGS cell. By controlling the tilting angle of the photonic crystal film, it achieves the generated electric power of 40.2 W m-2 and the irradiance of 124.6 W m-2 for transmitted photosynthetic lights (400–500 and 600–700 nm). In contrast, a conventional horizontal CIGS cell shows a power generation of 55.6 W m-2 without any light transmission. This work provides a new optical strategy and design principle for the development of a wavelength-selective semitransparent solar cell.

Polymer nanocomposite for protecting photovoltaic cells from solar ultraviolet in space

Abstract Polymer nanocomposite coatings of solar photovoltaic cells that absorb solar ultraviolet (UV) radiation and convert it into visible and near-infrared (NIR) light can increase the operational lifetime and the energy efficiency of the cells. We report a polymer nanocomposite spectrum converting layer (SCL) made of colorless polyimide CORIN impregnated with the nanoparticles (NPs) of fluoride NaYF4 doped with three-valent ions of Europium at a molar concentration of 60%. The NPs were the nanocrystals (179 ± 35 nm in size) in thermally stable hexagonal beta-phase. The visible-NIR photoluminescence quantum yield of the nano-powder was ∼69%. The SCLs were applied using the open-air multi-beam multi-target pulsed laser deposition method to silicon heterojunction (SHJ), copper-indium-gallium-selenide (CIGS), and inverted metamorphic multijunction (IMM) solar cells. The cells were exposed to UV radiation from a 365 nm light emitting diode. The I–V characteristics of the cells were measured with a solar simulator using AM0 filter. The proposed SCLs improved the UV stability of all three types of the cells: the power degradation of SHJs and IMMs cells was stopped or slightly reversed and the degradation rate of CIGSs decreased by ∼25%. The proposed SCLs have great commercial potential, especially for applications to space power.

Sputtered NiO Interlayer for Improved Self‐Assembled Monolayer Coverage and Pin‐Hole Free Perovskite Coating for Scalable Near‐Infrared‐Transparent Perovskite and 4‐Terminal All‐Thin‐Film Tandem Modules

The use of carbazole‐based self‐assembled monolayer (SAM) as a hole transport layer (HTL) has led to the efficiency advancement in p–i–n perovskite solar cells (PSCs). However, PSCs with SAM HTL display a large spread in device performance even on small‐area substrates owing to poor SAM surface coverage and dewetting of the perovskite ink. Efforts to improve the uniformity in device performance of SAM‐based PSCs have been confined to spin‐coating method, which lacks high‐throughput capabilities and leads to excessive material wastage. Herein, a scalable bilayer HTL stack with sputtered NiO and blade‐coated SAM is utilized to achieve improved SAM coverage and accomplish uniform coating of perovskite absorber on 5 cm × 5 cm substrates. Fully scalable p–i–n PSCs with efficiency close to 19% with a minimal spread in device performance are achieved. To showcase the upscaling potential, near‐infrared‐transparent perovskite mini‐modules with efficiency close to 15% and 13% are achieved on an aperture area of 2.56 and 12.96 cm2. Together with low‐bandgap (1.0–1.1 eV) Cu(In,Ga)Se2 (CIGS) mini‐modules, the first fully scalable 4‐terminal perovskite‐CIGS tandem mini‐module with an efficiency of 20.5% and 16.9% on an aperture area of 2.03 and 10.23 cm2 is demonstrated.

Suppressing interface recombination via element diffusion regulation towards high-efficiency Cd-free Cu(In,Ga)Se2 solar cells

Magnetron-sputtered Zn1-xMgxO (ZMO) films suffer from severe elemental diffusion to Cu(In,Ga)Se2 (CIGS), which limits the further improvement of device performance. Herein, we introduced Zn(O,S) (ZOS) as a barrier layer, and we controlled the diffusion of Zn within an appropriate range by adjusting the annealing temperature of ZOS. The results indicate that Zn can occupy copper vacancies (VCu) in CIGS and easily diffuse through VCu. A moderate amount of Zn at the interface acts as a charge compensator, reducing the band tailing effect and promoting the carrier collection efficiency of photovoltaic (PV) devices. However, excessive Zn doping induces additional defects dominated by ZnCu, ZnGa and ZnIn, leading to severe nonradiative recombination. Consequently, the Cd-free CIGS solar cell produced based on these insights exhibited a 49.4-mV reduction in the Voc deficit (Voc,def) as well as a notable increase in the power conversion efficiency (PCE) to 18.0 %. This study is the first to reveal the mechanism of defects caused by Zn diffusion, and these findings provide theoretical support for the study of Cd-free thin-film solar cells.

Nitrogen-doped graphene quantum dots/ polyvinyl alcohol nanocomposite for photon management: Application in CIGS photovoltaic cells

The efficiency (η) of copper indium gallium selenide (CIGS) solar cells has been hampered by absorption losses that happen within the ZnO and CdS layers. A photon downconversion layer created from polyvinyl alcohol (PVA) and nitrogen-doped graphene quantum dots (NGQDs) composite (NGQDs/PVA) was implemented on the top of the cell to overcome this obstacle. Notably, the NGQDs/PVA layers, prepared at spin speeds of 3000, 4000, and 5000 rpm, exhibited optimal characteristics, demonstrating superior light absorption at low wavelengths along with elevated transmittance at longer wavelengths. The η was found to be highest for the layer prepared at 4000 rpm, accompanied by elevated values of short-circuit current (Jsc), open-circuit voltage (Voc), and fill factor (FF). Consequently, Cell #2 incorporating the champion NGQDs/PVA layer outperformed all other CIGS photovoltaic cells, showcasing an impressive enhancement of 8.96 % in Jsc, 1.62 % in Voc, 2.03 % in FF, and an overall η of 11.51 %. This champion cell significantly improves the performance of CIGS photovoltaics.

Development of a Plasmonic Light Management Architecture Integrated within an Interface Passivation Scheme for Ultrathin Solar Cells

In response to climate and resource challenges, the transition to a renewable and decentralized energy system is imperative. Ultrathin Cu(In,Ga)Se2 (CIGS)‐based solar cells are compatible with such transition due to their low material usage and improved production throughput. Despite the benchmark efficiency of CIGS technology, ultrathin configurations face efficiency drops arising from increased rear interface recombination and incomplete light absorption. Dielectric passivation schemes address rear interface recombination, but achieving simultaneous electrical and optical gains is crucial for thinning down the absorber. Plasmonic nanoparticles emerge as a solution, enhancing light interaction through resonant scattering. In the proposed architecture, the nanoparticles are encapsulated within a dielectric rear passivation layer, combining effective passivation and light trapping. A controlled deposition and encapsulation of individualized nanoparticles is achieved by an optimized process flow using microfluidic devices and nanoimprint lithography. With the developed plasmonic and passivated architecture, a 3.7 mA cm−2 short‐circuit current density and a 23 mV open‐circuit voltage improvements are obtained, leading to an almost 2% increase in light‐to‐power conversion efficiency compared to a reference device. This work showcases the developed architecture potential to tackle the electrical and optical downfalls arising from the absorber thickness reduction, contributing to the dissemination of ultrathin technology.

Evidence of Cationic Antiphase Disorder in Epitaxial Cu(In,Ga)S2 Grown on GaP/Si(001)

A transmission electron microscopy study of epitaxial Cu(In,Ga)S2 (CIGS) films coevaporated on GaP/Si(001), in either Cu‐rich or Cu‐poor conditions, is presented. The spatial distribution and the orientation of the different phases by means of electron diffraction are unveiled. From atomically resolved imaging of the CIGS film's atomic structure, it is concluded that different chalcopyrite domains, sharing cation antiphase symmetries of the cation sublattice, coexist in the films. At least three types of cation antiphase boundaries (CAPBs), which do or do not lead to a violation of the octet rule, depending on the propagation direction, are conceptualized. Even though it is observed that epitaxial CIGS is highly prone to cation antiphase disorder (CAPD), and it is found that the growth of CIGS in Cu‐rich conditions leads to a lower density of CAPBs, as compared to Cu‐poor growth conditions. This opens the question of the influence of CAPBs on CIGS electronic properties.

A Review of Perovskite/Copper Indium Gallium Selenide Tandem Solar Cells

In recent years, perovskite solar cells (PSCs) have emerged as a focal point for numerous researchers due to their excellent photoelectric performance. In comparison to their single‐junction devices, double‐junction cells have exhibited the potential for superior power conversion efficiency (PCE). Copper indium gallium selenide (CIGS) solar cells, a well‐established photovoltaic technology, can be used as a viable bottom cell candidate for double‐junction tandem solar cells (TSCs). Recently, the PCE of the most advanced 4T perovskite/CIGS TSCs reached 29.9%, while the highest PCE of 2T perovskite/CIGS TSC is 24.2%, which develops relatively slowly. In contrast to the leading perovskite/silicon (Si) TSCs in terms of PCE (PCE2T = 33.9%, PCE4T = 30.35%), perovskite/CIGS TSCs exhibit distinctive advantages such as adjustable bandgap, high absorption coefficient, radiation resistance, and can be prepared on flexible substrates. Building upon these advantages, the optimization process in four‐terminal and two‐terminal perovskite/CIGS TSCs is elucidated, the key technologies and challenges in material, structure, and photoelectric performance of the tandem cells are summarized, and a prospective analysis of their future overall development in this review is provided. Furthermore, it is hoped to give readers a comprehensive understanding of perovskite/CIGS TSCs.

Fabrication of Pre-Structured Substrates and Growth of CIGS Micro-Absorbers.

Second-generation thin-film Cu(In, Ga)Se2 (CIGS) solar cells are a well-established photovoltaic technology with a record power conversion efficiency of 23.6%. However, their reliance on critical raw materials, such as In and Ga, requires new approaches to reduce the amount of critical raw materials employed. The micro-concentrator concept involves the combination of thin-film photovoltaic technology with concentrator photovoltaic technology. This approach reduces the size of the solar cell to the micrometer range and uses optical concentration to collect sunlight from a larger area, focusing it onto micro solar cells. This work is devoted to the development of a process for manufacturing pre-structured substrates with regular arrays of holes with 200 and 250 µm diameters inside a SiOx insulating matrix. Subsequently, a Cu-In-Ga precursor is deposited by sputtering, followed by photoresist lift-off and the application of a Cu-In-Ga thermal annealing at 500 °C to improve precursor quality and assess pre-structured substrate stability under elevated temperatures. Finally, a two-stage selenization process leads to the formation of CIGS absorber micro-dots. This study presents in detail the fabrication process and explores the feasibility of a bottom-up approach using pre-structured substrates, addressing challenges encountered during fabrication and providing insights for future improvements in CIGS absorber materials.

Aluminum‐Based Chalcopyrite Thin Films and Solar Cells

AbstractAluminum‐based chalcopyrite materials have attracted attention because of the wide controllability range of their material properties and potential for use in energy‐conversion devices. Herein, CuAlSe2‐based thin‐film growth and solar cell device properties are discussed. Ternary CuAlSe2 thin films are relatively unstable and decompose weeks after film growth, even when preserved in a dry box. However, alloying with elemental In led to significant improvements in stability. Cu(In,Al)Se2 (CIAS) solar cells yield better photovoltaic performance than CuInSe2 cells, although the effective range of Al concentration that can improve device performance is narrower than that of elemental Ga in Cu(In,Ga)Se2 (CIGS). A decrease in the alkali metal concentration in CIAS films with increasing Al concentration is observed, indicating that the formation energy of alkali‐metal substitutional defects on the Cu site is high, and/or Al‐related complex defects formed are kinetically stable and difficult to replace with alkali metals once they form. Although the direct observation of alkali metals in the bulk (grain interior) of chalcopyrite CuInSe2 and CIGS films has been difficult to date, this result can serve as indirect evidence of the presence of alkali metals in the bulk of CuInSe2 films.

A Deep Dive into Cu2ZnSnS4 (CZTS) Solar Cells: A Review of Exploring Roadblocks, Breakthroughs, and Shaping the Future.

Renewable energy is crucial for sustainable future, and Cu2ZnSnS4 (CZTS) based solar cells shine as a beacon of hope. CZTS, composed of abundant, low-cost, and non-toxic elements, shares similarities with Cu(In,Ga)Se2 (CIGS). However, despite its promise and appealing properties for solar cells, CZTS-based solar cells faces performance challenges owing to inherent issues with CZTS material, and conventional substrate structure complexities. This review critically examines these roadblocks, explores ongoing efforts and breakthroughs, providing insight into the evolving landscape of CZTS-based solar cells research. Furthermore, as an optimistic turn in the field, the review first highlights the crucial need to transition to a superstrate structure for CZTS-based single junction devices, and summarizes the substantial progress made in this direction. Subsequently, dive into the discussion about the fascinating realm of CZTS-based tandem devices, providing an overview of the existing literature as well as outlining the possible potential strategies for enhancing the efficiency of such devices. Finally, the review provides a useful outlook that outlines the priorities for future research and suggesting where efforts should concentrate to shape the future of CZTS-based solar cells.

Impact of Band‐gap Gradient in Semi‐Transparent and Bifacial Ultra‐Thin Cu(In,Ga)Se2 Solar Cells

AbstractUltra‐thin Cu(In,Ga)Se2 (CIGSe) solar cells on transparent conductive oxide back contact reduce the material consumption of rare indium and gallium and simultaneously exhibit great potential for semi‐transparent bifacial application. For highly efficient CIGSe solar cells, a steep back Ga grading and Na treatment are expected. However, Na will promote the formation of highly resistive GaOx at the rear interface owing to Ga accumulation. In this work, the three‐stage co‐evaporation process is renewed and the effect of the deposition sequence in the first stage on the Ga distribution as well as the cross‐correlated influence of Na is explored. In particular, the standard deposition sequence of Ga+In is altered to start with In. When a thin In layer is pre‐deposited on the back contact, the fill factor and efficiency increase. The deposition of In+Ga+In in the first stage of CIGSe growth leads to efficiencies 28% (on average) higher than for the standard deposition sequence of Ga+In. Additionally, 2.74% efficiency is reached under rear and 9.32% under simultaneous front and rear illumination. Therefore, adapting the deposition sequence in the first stage of CIGSe growth is identified as a key to improving the device performance on transparent back contact.

The Energy Level Alignment at the Buffer/Cu(In,Ga)Se2 Thin‐Film Solar Cell Interface for CdS and GaOx

AbstractSputter‐deposited GaOx (i.e., oxygen‐deficient gallium oxide) films are evaluated as a potential replacement for the standard CdS buffer layers in Cu(In,Ga)Se2 (CIGSe) based thin‐film photovoltaics. The energy level alignment at the GaOx/CIGSe and CdS/CIGSe interfaces are compared by means of direct and inverse photoemission. For the GaOx/CIGSe a (0.04 ± 0.07) eV (i.e., a small spike‐like) conduction band offset (CBO) and a (−3.21 ± 0.19) eV (i.e., a large cliff‐like) valence band offset (VBO) are found, which suggests a nearly ideal charge‐selective contact. The derived GaOx band gap of (4.80 ± 0.25) eV confirms its utility as a highly transparent buffer layer. However, the GaOx (with x derived to be 1.1 ± 0.1) exhibits considerable (presumably) defect‐related occupied states above the valence band maximum. It is proposed that these states may increase charge carrier recombination and decrease open circuit voltage in respective devices; also explaining why solar cells with standard CdS buffer outperform devices with GaOx buffer, despite less ideal electronic interface properties (CBO: (−0.18 ± 0.07) eV, VBO: (−0.98 ± 0.15) eV) and the smaller CdS band gap of (2.35 ± 0.22) eV.

An analytical study on the effect of different photovoltaic technologies on enviro-economic parameter and energy metrics of active solar desalting unit

The enviro-economic and energy metrics analyses of the solar system by incorporating different photovoltaic technologies are required to fulfill the sustainable development goal of the United Nations. However, the effect of different photovoltaic technologies on the solar distillation system has not been informed by any of the researchers to date. This research gap has been explored in this study. The present manuscript is an endeavour to explore the best photovoltaic technology aimed at a single-slope solar desalting unit comprised of N identical photovoltaic thermal flat-plate-collectors. Data regarding all four weather conditions for a year for New Delhi's climate have been procured from the Indian Meteorological Department situated in the western part of India. Fundamental equations along with input data have been provided to a computational code developed in MATLAB for the estimation of various performance parameters. Concludingly, the energy payback time is minimum (1.64 years) for the case of copper indium gallium selenide photovoltaic technology, however, maximum values of life cycle conversion efficiency and net CO2 mitigation are respectively 0.171 and 199.10 tons of CO2 for the case of crystalline silicon photovoltaic technology. The carbon credit is also found to be a maximum (15269.25 US$) for crystalline silicon photovoltaic technology.

Comparison of polycrystalline and epitaxial Cu(In, Ga)Se2 solar cells with conversion efficiencies of more than 21%

Polycrystalline Cu(In,Ga)Se2 (CIGS) solar cells are widely studied for their application in thin-film photovoltaics, but analysis of their crystalline properties is difficult owing to the presence of grain boundaries and defects. Epitaxial CIGS (epi-CIGS) solar cells can potentially address the issues of polycrystalline CIGS (poly-CIGS) solar cells, but their conversion efficiency has not been widely studied. We fabricated epi-CIGS layers using techniques developed for high-efficiency ploy-CIGS solar cells such as Ga grading, Na doping, and heat-light soaking. Here, scanning transmission electron microscopy and secondary ion mass spectrometry were used to compare the structural characteristics of poly- and epi-CIGS solar cells with conversion efficiencies of more than 21%. Both types of solar cells had similar Ga gradient profiles, and abrupt interfaces were observed between the CIGS and Mo, CIGS and GaAs, and CdS and CIGS layers. The poly-CIGS layer had a higher Na concentration than the epi-CIGS layer because the grain boundaries of the former included high concentrations of Na ions. Meanwhile, the Na ions in the epi-CIGS layer promoted the interdiffusion of In and Ga. For both types of solar cells, heat-light soaking increased the carrier concentration by more than 1 × 1017 cm−3. These observations suggest that grain boundaries are not the main factor limiting the conversion efficiency of poly-CIGS solar cells.