CuInS2 Solar Cells Research Articles

Implantation assisted copper diffusion: A different approach for the preparation of CuInS2∕In2S3 p-n junction

Copper indium sulfide thin films were prepared using copper diffusion into argon ion implanted In2S3 thin films. A comparative study of copper diffusion in pristine and ion implanted In2S3 samples was also performed. It was found that copper indium sulfide formation was much better in argon implanted samples compared to that in unimplanted samples. Copper diffusion in implanted samples enabled us to prepare an In2S3∕CuInS2 solar cell. The fill factor of the cell prepared was 30.2% and the efficiency was 0.34%.

Efficient CuInS2 solar cells by reactive magnetron sputtering

We demonstrate CuInS2 thin film solar cell device efficiencies larger than 10% by preparing the absorber layers by reactive magnetron sputtering from metallic targets in an argon-hydrogen sulfide atmosphere. At deposition temperatures below 500°C the polycrystalline films show a compact morphology with grain sizes of several micrometers. Solar cell devices show optical and electrical properties that are comparable to coevaporated or sequentially processed cells, in particular, diffusion lengths larger than 2μm and fill factors larger than 70%. We conclude that ion bombardment during the sputtering process does not lead to a significant increase of electronically active defects in these devices.

Efficient CuInS2 (CIS) solar cells by photoelectrochemical conditioning

Nous presentons deux approches pour remplacer le decapage par le compose toxique KCN dans la production des couches de CuInS 2 utilisees comme absorbant dans les cellules solaires (CIS). Le traitement electrochimique dans un electrolyte acide contenant le couple V 2 + /V 3 + comprend deux etapes : la premiere consiste a enlever le covellite (CuS) a des potentiels anodiques moderes et la seconde a dissoudre une petite couche sacrificielle de CIS ainsi que des restes de sulfures de cuivre a des potentiels plus agressifs. Cette procedure permet d'obtenir des couches absorbantes offrant un rendement de 3,3 % dans les cellules solaires photoelectrochimiques et de 8% dans des dispositifs a l'etat solide. L'autre approche combine traitements electrochimique et chimique : l'energie libre de formation du complexe Cu-EDTA contribue a la dissolution du sulfure de cuivre et facilite l'enlevement de la phase Cu-S a des potentiels electrochimiques moderes. Les couches de CIS obtenus apres ce traitement offrent un rendement de 1,44% dans des cellules solaires photoelectrochimiques.

Optical, Structural and Electronic Properties of CuInS2 Solar Cells Deposited by Reactive Magnetron Sputtering

AbstractCuInS2 thin films have been prepared by reactive magnetron sputtering from metallic targets in an Ar/H2S atmosphere. The Cu/In ratio and substrate temperature have been varied and absorber layers were processed to solar cell devices using the HMI baseline process. Device efficiencies up to 8.8 % have been achieved. The electronic and optical properties of the solar cell devices were analyzed by Scanning Electron Microscopy, Raman, photoluminescence, current-voltage and quantum efficiency measurements. Raman measurements indicate that Cu-Au defect ordering is present in some of the films, which can be eliminated by appropriate choice of the growth parameters. Photoluminescence measurements show spectra very similar to the spectra found for cells from the two-step sequential process indicating a similar defect structure in these films. No principle obstacles to establishing a one-step reactive magnetron sputtering process for CuInS2 solar cell absorbers have been identified.

8% efficient CuInS2 solar cells by electrochemically removed Cu–S Phases

Investigations on how to replace the toxic KCN etching for the removal of Cu–S phases during the preparation of CuInS2 (CIS) absorber layers by electrochemical procedures are presented. Starting from a simple anodic treatment in V2+/V3+ electrolyte, a more complex photoelectrochemical technique is developed which consists of different consecutive etching steps for the dissolution of the predominant CuS and for the removal of remaining Cu2S and a small sacrificial layer of CuInS2. This new method also offers the possibility of in situ quality control of the CIS in a photoelectrochemical solar cell (PECS) setup. Further examination of the treated films is carried out using X-ray emission spectroscopy, X-ray photoelectron spectroscopy (XPS) and by further processing of the samples to create solid state solar cells. The specimen yield conversion efficiencies of 3.3% in PECS and 8% in solid state devices.

Valence band alignment with a small spike at the CuI/CuInS2 interface

From the point of view of the “doping pinning rule,” application of p-type buffer layer materials for CuInS2 solar cells may lead to record levels of cell efficiency due to an optimal band offset at the interface. Under simplified simulation conditions, an increase in efficiency of up to about 18% was predicted. Evaluation of the valence band offset between CuI and single crystalline CuInS2 by photoelectron spectroscopy displays a spike height of (0.1±0.2) eV, optimal for solar cell applications. The positions of the valence band edge were determined by assuming a parabolic distribution of the density of states.

Defect Distribution of CuInS2 Solar Cells from Different Preparation Processes as Determined by Admittance Spectroscopy

Admittance spectroscopy measurements are carried out to determine the defect spectra of CuInS2 solar cells from different preparation methods. Different defects are found and partly interpreted in terms of interface and bulk defects with the help of annealing experiments and DLTS measurements. A correlation between defect spectrum and open-circuit voltage is found. We further examine the origin of series resistances that influence the measurement of capacitance.

Size-quantized CdS films in thin film CuInS2 solar cells

Semiconductor quantum dots and wires are the subject of great interest, mainly due to their size-dependent electronic structures, in particular increased band gap and therefore optoelectronic properties. We have electrodeposited films of size-quantized CdS (∼4 to 5 nm cross section by 15 nm height) as a buffer layer on CuInS2. The resulting CuInS2/CdS thin-film solar cells gave increased photocurrents and higher light-to-electricity conversion efficiencies (>11%) than those made with conventional nonquantized CdS films. This was due mainly to the increased band gap of the quantized CdS, allowing more light to reach the active CuInS2 layer.

Photoluminescence of CuInS2 thin films and solar cells modified by postdeposition treatments

The photoluminescence of CuInS2 thin films and solar cells is investigated as a function of postdeposition treatments for different temperatures and excitation intensities. Annealing in hydrogen atmosphere causes an increase of PL intensity at 1.445 eV by more than a factor of 100, while subsequent annealing in oxygen or air ambient passivates this transition, which is ascribed to a donor-acceptor pair recombination between a sulphur vacancy and a copper vacancy. A defect mechanism is suggested that assumes the passivation of sulphur vacancies by oxygen in grain surfaces which can be activated by hydrogen annealing.

Solar Cells Based on CuInS2 Thin Films through Sulfurization of Precursors Prepared by Reactive Sputtering with H 2S Gas

CuInS2 films were prepared using a two-stage process in which Cu–In–S precursors were sputtered in H2S/Ar with metal targets (Cu and In) and then annealed in H2S atmosphere. Control of S content in the precursor is essential for fabricating high-quality CuInS2 films and achieving high-efficiency solar cells. When S/(Cu+In) ratio in the precursor was about 0.3, CuInS2 films with good crystallinity and smooth surface were obtained, and consequently a CuInS2 solar cell with an efficiency of 6.3% has been achieved without KCN treatment.