Chalcopyrite thin film solar cells by electrodeposition

Among the armoury of photovoltaic materials, thin film heterojunction photovoltaics continue to be a promising candidate for solar energy conversion delivering a vast scope in terms of device design and fabrication. Their production does not require expensive semiconductor substrates and high temperature device processing, which allows reduced cost per unit area while maintaining reasonable efficiency. In this regard, superstrate CdTe/CdS solar cells are extensively investigated because of their suitable bandgap alignments, cost effective methods of production at large scales and stability against proton/electron irradiation. The conversion efficiencies in the range of 6–20% are achieved by structuring the device by varying the absorber/window layer thickness, junction activation/annealing steps, with more suitable front/back contacts, preparation techniques, doping with foreign ions, etc. This review focuses on fundamental and critical aspects like: (a) choice of CdS window layer and CdTe absorber layer; (b) drawbacks associated with the device including environmental problems, optical absorption losses and back contact barriers; (c) structural dynamics at CdS–CdTe interface; (d) influence of junction activation process by CdCl2 or HCF2Cl treatment; (e) interface and grain boundary passivation effects; (f) device degradation due to impurity diffusion and stress; (g) fabrication with suitable front and back contacts; (h) chemical processes occurring at various interfaces; (i) strategies and modifications developed to improve their efficiency. The complexity involved in understanding the multiple aspects of tuning the solar cell efficiency is reviewed in detail by considering the individual contribution from each component of the device. It is expected that this review article will enrich the materials aspects of CdTe/CdS devices for solar energy conversion and stimulate further innovative research interest on this intriguing topic.

Physics and chemistry of CdTe/CdS thin film heterojunction photovoltaic devices: fundamental and critical aspects

Polycrystalline thin films of copper indium diselenide and its alloys with gallium and sulphur (CIGS) have proven to be suitable for use as absorbers in high-efficiency solar cells. Record efficiency devices of 20% power conversion efficiency have been produced by co-evaporation of the elements under high vacuum. However, non-vacuum methods for absorber deposition promise significantly lower capital expenditure and reduced materials costs, and have been used to produce devices with efficiencies of up to 14%. Such efficiencies are already high enough for commercial up-scaling to be considered and several companies are now trying to develop products based on non-vacuum deposited CIGS absorbers. This article will review the wide range of non-vacuum techniques that have been used to deposit CIGS thin films, highlighting the state of the art and efforts towards commercialization.

Non‐vacuum methods for formation of Cu(In, Ga)(Se, S)2 thin film photovoltaic absorbers

CuInSe2 and its alloys with Ga and/or S are among the most promising absorber materials for thin film solar cells. CuInSe2-based solar cells have shown long-term stability and the highest conversion efficiencies of all thin film solar cells, above 19%. Solar cells based on these materials are also very stable, thus allowing long operational lifetimes. The preparation of a thin film solar cell is a multistage process where every step affects the resulting cell performance and the production cost. CuInSe2 and other Cu chalcopyrites can be prepared by a variety of methods, ranging from physical vapor deposition methods such as evaporation and sputtering to low-temperature liquid phase methods such as electrodeposition. The present review discusses first the concept and operation principle of thin film solar cells, as well as the most important thin film solar cell materials. Next, the properties of CuInSe2 and related compounds, as well as features of solar cells made thereof are reviewed. The last ...

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Thin Film Deposition Methods for CuInSe2Solar Cells

Effect of film thickness on microstructure parameters and optical constants of CdTe thin films

Electrodeposition of p–i–n type CuInSe2 multilayers for photovoltaic applications

Making use of the authors' experimental results and the evidence available in the literature, an alternative model for glass/conducting glass/CdS/CdTe/metal solar cells has been formulated. This model explains the device behaviour in terms of a combination of a hetero-junction and a large Schottky barrier at the CdTe/metal interface. The main experimental observations available to date are described and compared with the currently assumed p–n junction model and this proposed new model. It is shown that the proposed model explains almost all the experimental results more satisfactorily. The paper describes the guidelines to further increase the performance efficiencies based on the new model. Following these new guidelines, the authors have fabricated improved devices producing open circuit voltage (Voc) values over 600 mV, fill factor (FF) values over 0.60 and the short-circuit current density (Jsc) values over 60 mA cm−2 for best devices. Although the Voc and FF could be further improved, the remarkable improvement of Jsc indicates the possibility of further development of multilayer graded band gap tandem solar cells based on CdS/CdTe system.

https://iopscience.iop.org/article/10.1088/0268-1242/17/12/306/pdf

New ways of developing glass/conducting glass/CdS/CdTe/metal thin-film solar cells based on a new model

Electrodeposition of p+, p, i, n and n+-type copper indium gallium diselenide for development of multilayer thin film solar cells

ZnSe layers have been grown by a low temperature (∼65 °C) electrochemical deposition technique in an aqueous medium. The resulting thin films have been characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive analysis by X-rays (EDAX), glow discharge optical emission spectroscopy (GDOES) and X-ray fluorescence (XRF) for bulk material properties. A photo-electrochemical (PEC) cell and an optical absorption method have been used for determination of the electrical and optical properties of the thin films. XRD patterns indicate the growth of ZnSe layers with (1 1 1) as the preferred orientation. The XPS spectra are similar to those of commercially available ZnSe and the EDAX, GDOES and XRF also indicate the presence of Zn and Se in the layers. PEC studies show p-type semiconducting properties for the as deposited layers and n-type ZnSe can be produced by appropriate doping. Optical absorption is maximum around 460 nm indicating a band gap of 2.7 eV. Annealing at 200 °C for 15 mins improves both the crystallinity of the layers and the photoresponse of the electrolyte/ZnSe liquid/solid Schottky junction. © 1998 Chapman & Hall

Growth of n-type and p-type ZnSe thin films using an electrochemical technique for applications in large area optoelectronic devices

ZnSe layers have been grown by a low temperature (∼65 °C) electrochemical deposition technique in an aqueous medium. The resulting thin films have been characterized using X-ray diffraction (XRD) and a photoelectrochemical (PEC) cell for determination of the bulk properties and electrical conductivity type. XRD patterns indicate the growth of ZnSe layers with (1 1 1) as the preferred orientation. PEC studies show p-type semiconducting properties for the as deposited layers and n-type ZnSe can be produced by appropriate doping. Annealing at 250 °C for 15 min improves the crystallinity of the layers and the photoresponse of the ZnSe/electrolyte junction. © 1998 Kluwer Academic Publishers

J. Young

Papers

Electrodeposition of p–i–n type CuInSe2 multilayers for photovoltaic applications

New ways of developing glass/conducting glass/CdS/CdTe/metal thin-film solar cells based on a new model

Electrodeposition of p+, p, i, n and n+-type copper indium gallium diselenide for development of multilayer thin film solar cells

Growth of n-type and p-type ZnSe thin films using an electrochemical technique for applications in large area optoelectronic devices

Electrodeposition of n-type and p-type ZnSe thin films for applications in large area optoelectronic devices