CIS and CIGS based photovoltaic structures developed from electrodeposited precursors

In the present study we report the electrodeposition and characterization of CIS and CIGS thin films and a post-deposition thermal processing in vacuum to improve the film stoichiometry by incorporating additional In, Ga and Se. Different kinds of analyses showed that CIS as well as CIGS possess a very thin In-rich surface n-layer. The formation and characterization of solar cell structures from the electrodeposited precursor with the configuration glass/Cr/Mo/CIS(CIGS)/CdS/ZnO/MgF₂ is also reported. The optoelectronic properties such as Voc, Isc, FF, η etc. of the cells are presented.     

ZnSe thin films by chemical bath deposition method

The ZnSe thin films have been deposited onto glass substrates by the simple chemical bath deposition method using selenourea as a selenide ion source from an aqueous alkaline medium. The effect of Zn ion concentration, bath temperature and deposition time period on the quality and thickness of ZnSe films has been studied. The ZnSe films have been characterized by XRD, TEM, EDAX, TRMC (time-resolved microwave conductivity), optical absorbance and RBS techniques for their structural, compositional, electronic and optical properties. The as-deposited ZnSe films are found to be amorphous, Zn rich with optical band gap, Eg, equal to 2.9 eV.     

The effects of the morphology on the CIGS thin films prepared by CuInGa single precursor

Cu(In_xGa_1−x)Se₂ (CIGS) thin films were prepared by selenization of CuInGa single-layer metallic precursors. At the first stage, CuInGa metallic precursors were deposited onto soda lime glass by direct current (DC) magnetron sputtering system using a CuInGa ternary alloy target with a composition ratio of Cu:In:Ga of 1:0.7:0.3. The precursor films were reacted with Se vapor in vacuum evaporation system. By means of X-ray diffraction (XRD), field emission scanning electron microscope (SEM) and electron probe microanalysis (EPMA), it was found that CIGS thin films exhibit large facetted grains and single chalcopyrite phase with preferred orientation along (1 1 2) plane. Meanwhile, the surface roughness of the CIGS films can be determined by the morphology of the precursor films.     

Impacts of pulsed-laser assisted deposition on CIGS thin films and solar cells

We have proposed a novel laser-assisted-deposition (LAD) process for improving the crystalline quality of CIGS thin films and cell performance. The influences of laser power, Ga content in CIGS, substrate temperature, and photon energy of laser on CIGS thin films and solar cells have been investigated. In the LAD process a pulsed excimer laser and a pulsed Nd:YAG laser were irradiated onto the substrate surface during CIGS deposition by the three-stage process. The crystalline quality of CIGS thin films and cell performance, particularly open-circuit-voltage, improved by LAD process for all ranges of Ga content and at substrate temperature ranges of 400-550 °C. It was also found that the laser irradiation enhanced the diffusion of Ga into CIGS even at low substrate temperatures, which strongly affects the formation of double-graded bandgap. The PL decay time of LAD-CIGS solar cells was much longer than that of the fabricated by the three-stage process, which implies the reduced defects in CIGS absorber layer. The improved thin-film quality and cell performance became noticeable only when the laser wavelength was shorter than 266 nm (4.66 eV of photon energy). This result strongly suggests that the impacts of pulsed-laser irradiation are dominated by photon-energy rather than thermal-energy.     

Low cost processing of CIGS thin film solar cells

A set of low cost techniques with realistic potential for direct manufacturing costs reduction were developed in the last five years while the industrial Cu(In,Ga)Se₂ (CIGS) solar cell production is based on vacuum processes, which require high initial investment into production machines. The common properties of these low cost techniques are the use of simple and fast non-vacuum deposition methods and the prefixing of the film-composition on a molecular level in a precursor layer, which is chemically and thermally treated to form a high quality CIGS film. The paste coating approaches use premixed inks which are applied by doctor-blade coating to yield solar cell efficiencies of 13.6%, with the potential to reach 15% and more in the next years. The choice of the precursor material has to be made with respect to the used selenization conditions to avoid detrimental impurity phases. A new precursor material is discussed, which allows fast conversion in selenium atmosphere and was used to produce solar cells with 6.7% efficiency. The CIGS film thickness has to be increased for complete absorption of the incident light.     

Physical properties of chemical bath deposited CdS thin films

Cadmium sulfide films of different thicknesses were deposited by chemical bath deposition (CBD) from a bath containing cadmium chloride, ammonium chloride, ammonium hydroxide and thiourea. The XRD patterns show that the films have a hexagonal phase with a preferential (0 0 2) orientation. The photoluminescence spectra show a defect structure, characteristics of the CdS films obtained by CBD. The electrical behavior in dark and under illumination, the optical properties and the band gap value reported in this work is in agreement with that reported in the literature.     

Precursor modification for preparation of CIS films by selenization technique

CuInSe₂ films have been prepared using the selenization technique. Preparation of the precursor as well as selenization were carried out by the vacuum evaporation technique. The sequence of copper and Indium layer deposition during precursor preparation affects the morphological and structural properties of precursor which directly have effects on the properties of selenized CIS films. A thin layer of amorphous selenium at the substrate/film interface has been used to improve the adherence of the film. The effect of the Se under-layer has been studied on the layers of copper, indium, CuIn precursors and CIS films, using structural, morphological and optical properties. The surface morphology of a single layer of copper and indium, with and without the Selenium under-layer, are quite different and drastically affect the properties of the precursor and selenized films. The Se under-layer does not take part in the chemical reaction of CIS formation during the selenization process. The modified CIS films are uniform, single phase, polycrystalline, chalcopyrite with (1 1 2) preferred orientation showing an energy band gap of 0.99 eV and an absorption coefficient of 10⁵ cm⁻¹, and have good adherence to the substrate for the scotch tape test.     

CIS(CIGS)太阳能电池研究进展

介绍了CIS（CIGS）薄膜太阳能电池的性能与结构以及制备方法、掺杂对电池的性能与结构的影响、窗口层的制备等方面的最新研究成果，重点介绍了两种低成本制备薄膜的方法：电沉积法和喷雾法，最后阐述了CIS（CIGS）太阳能电池在工业生产和空间应用的进展情况，并展望了CIS（CIGS）发展趋势。     

A CdTe/PMeT photovoltaic structure formed by electrodeposition and processing

CdTe thin films were electrodeposited from an ethylene-glyco-based bath by the galvanostatic method. As-deposited and tellurized films were characterized by structural, optoelectronic and photoelectrochemical methods. The film stoichiometry improved after tellurization of the film at 300°C by a technique called chemical vapor transport by Gas (CVTG) in a tubular furnace. Tellurized films showed near stoichiometry with p-type conductivity in the bulk and n-type surface conductivity. Schottky barrier type photovoltaic junctions were obtained using a heavily doped PMeT (poly-3(methylthiophene), prepared by electropolymerization, displaying nearly metallic behavior, and CdTe obtained by electrodeposition. A solar to electrical conversion efficiency of the order of 1% was obtained in the case of PMeT/CdTe junction.     

Electrodeposition of ZnO thin films by using molecular oxygen and hydrogen peroxide as oxygen precursors: Structural and optical properties

Zinc oxide thin films were potentiostatically electrodeposited from a ZnCl₂+LiCl bath using two different oxygen precursors: molecular oxygen and hydrogen peroxide. X-ray diffraction (XRD) studies confirmed the presence of the ZnO wurtzite structure with marked preferential orientation along the (0 0 2) axis. The optical transmittance shows a clear absorption edge in the ultraviolet (UV) region which corresponds to an energy band gap of 3.41±0.03 eV. As a general rule the higher band gap energies are related to the more transparent films.     

New ultra thin CIGS structure solar cells using SCAPS simulation program

The present contribution reports on the performances of ultra thin chalcopyrite Cu (In,Ga) Se (CIGS) solar cells. An alternative ZnO/CdS/CIGS/Si structure has been proposed using solar cell capacitance simulator (SCAPS). The main idea behind this analysis is the improvement of the device efficiency using materials cheaper than conventional CIGS. For that purpose, a 1 μm of a new layer p-Si has been added. Various thicknesses of CIGS absorber layer ranging from 0.1 to 1 μm have been used. Our findings showed that the increase of the absorber layer thickness leads to the improvement of the performance of the new CIGS solar cells. It was found that the best structure must have a window layer ZnO, a buffer layer (CdS), an absorbent layer (CIGS) and a Si layer with thicknesses of 0.02, 0.05, 1 and 1 μm, respectively. Cells with these features give conversion efficiency of 21.3%. The present results showed that the new ultra thin CIGS solar cells structure has performance parameters that are comparable to those of the conventional ones with reduced cost.     

CuInSe2 thin films deposited by UV laser ablation

Application of pulsed laser ablation method for deposition of CuInSe₂ films was studied. The special time–temperature regime was developed. The homogeneous amorphous and polycrystalline CuInSe₂ films were prepared and investigated with XRD, SEM-EDS and optical spectroscopy.     

Optical properties of electrodeposited CdTe thin films

The absorption coefficient spectra of the elctrodeposited CdTe thin films were analyzed and compared with that of the single crystal. Pinhole-free thin films facilitated the analysis of the high-energy regions of the absorption coefficient spectra. The various allowed direct and indirect transitions were detected successively by subtracting the extrapolated values of the lower-energy transitions. The effect of heat treatment on the optical transitions were analyzed with films annealed at 300°C in air, argon and CdCl₂.The direct band gap of the electrodeposited films decreased with increasing film thickness and approaches the value of the single crystal. The films annealed at different environments show slightly lower value for the band gap. Annealing in argon caused significant change in the optical transition spectra.     

Deposition of thin conducting films of CuI on glass

A method is described for coating thin optically transparent conducting films of CuI (p-type semiconductor of band gap 3.1 eV) on glass. The dependence of the sheet resistance of the film on the level of iodine doping and other characteristics of the film are described. A minimum sheet resistance 25 Ω/□ (for a film of thickness 10 μm) was obtained through an optimization of iodine doping, sintering time and temperature.     

CuInTe2 and In-rich telluride chalcopyrites thin films obtained by electrodeposition techniques

In order to obtain single-phase thin films of the system Cu–In–Te with optoelectronic properties adequate for solar cells, electrodeposition techniques were used on substrates of molybdenum supported by glass. Different annealings in Te atmosphere have been done that affect the Te concentration and In/Cu atomic ratio. Single chalcopyrite phase appears in two ranges of composition where the In/Cu atomic ratio varies between 0.21–0.76 and 0.90–3.46, respectively. Morphology, cell lattice parameters and electrical resistance for single-phase samples depend strongly on the composition in the annealed samples. The cell parameters ranges are a=6.141–6.183 Å and c=12.201–12.375 Å.     

Electrodeposited and selenized (CuInSe2) (CIS) thin films for photovoltaic applications

In the present communication, the authors report results on the characterization of electrodeposited and selenized (CuInSe₂) (CIS) thin films. The selenization process was carried out using a technique called chemical vapor transport by gas (CVTG). The precursors as well as selenized films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron microprobe analysis (EPMA). The film stoichiometry improved after selenization at 550°C. The films were formed with a mixed composition of the binary as well as the ternary phases.     

Photoelectrical properties of ZnS thin films deposited from aqueous solution using pulsed electrochemical deposition

ZnS is an n-type semiconductor with a wide direct band gap (3.7 eV at room temperature), and it is very suitable as a window layer in heterojunction photovoltaic solar cells. We deposited ZnS thin films on Sn-doped In₂O₃-coated glass substrate using pulsed electrochemical deposition (ECD) from aqueous solutions containing Na₂S₂O₃ and ZnSO₄ with two different compositions, the first group grown from ZnSO₄-rich solution, and the second grown from Na₂S₂O₃-rich solution. We investigated electrical properties of the ZnS thin films and properties of contacts with different metals evaporated on the surfaces. We found that Au and In contacts have Ohmic-like characteristics to ZnS. Furthermore, we observed photoconductivity of the ZnS thin films by means of photoelectrochemical (PEC) measurements. We found that for both the groups of ZnS thin films, the as-deposited film shows weak photosensitivity and after annealing at 300 °C the photosensitivity improved.     

RF magnetron sputtered ZnO:Al thin films on glass substrates: A study of damp heat stability on their optical and electrical properties

ZnO:Al thin films were deposited on glass substrates by RF magnetron sputtering from a powder compacted ceramic target. Structural, electrical and optical properties of the films with different thickness were characterized. The damp heat stability of ZnO:Al thin film was investigated for its application in thin-film solar cells. After the 1000 h damp heat treatment in harsh conditions of 85% relative humidity at 85 °C for all samples, a degradation of electrical properties was observed, while the transmissions of the films were almost unchanged. Thick films with a relative large grain size could form compact structure to resist the corrosion by oxygen and water molecules.     

Electrodeposition of tin selenide thin film semiconductor: effect of the electrolytes concentration on the film properties

Tin selenide semiconductor films have been potentiostatically deposited onto a tin substrate from an aqueous solution containing SnCl₂ and Na₂SeO₃. Deposition at various concentrations was attempted in order to investigate the effect of the electrolytes concentration on the film properties and to determine the optimum bath composition. The structure, morphology and photoactivity of the films were studied using X-ray diffraction, scanning electron microscopy and linear sweep photovoltammetry techniques. The semiconducting property of the deposit is strongly affected by the electrolytes concentration. The optimum bath composition was found to be 0.010 M for SnCl₂ and 0.015 M for Na₂SeO₃.