Chalcopyrite Semiconductor CuInSe2 Research Articles

Improved efficiency of Cu(In,Ga)Se2 thinfilm solar cells using a buffer layer alternative to CdS

The chalcopyrite semiconductor CuInSe2 and its constitutes Ga and/or S [Cu (InGa)Se2 or Cu (InGa)(Se,S)2], commonly referred as CIGS have been leading thinfilms for incorporation in high-efficiency photovoltaics. In conventional ZnO-N/i-ZnO/CdS/CIGS solar cells, the traditional CdS buffer is nearly optimum for the commonly used 1.15 eV (CIGS) but less optimal for higher Ga. To overcome this limitation, Cd1-yZnyS is proposed as an alternative buffer layer to replace the standard CdS in CIGS thinfilm solar cells containing an ordered vacancy compound (OVC) layer. Next, the dependence of solar cells performance on the change of Ga and Zn concentrations in absorber and buffer layers, respectively, was investigated using the AMPS-1D software. The results are potential improvement in CIGS efficiency that was obtained with replacement of CdS buffer material by its alternative in one hand, another hand by formation of OVC layer. Lastly, the optimum values of Ga and Zn concentrations were found at 0.7 and 0.6, respectively, leading to a high conversion efficiency of around 23.71%.

Preparation of In2S3Thin Films by MOCVD Using Single Source Precursors: Tris(N,N-ethylbutyldithiocarbamato)indium(III) and Tris(2-ethylpiperidinedithiocarbamato)indium(III)

The ternary chalcopyrite semiconductor CuInSe2 (CIS) or related Cu(In,Ga)Se2 (CIGS) are well known materials for high efficiency thin film solar cells. In case of CIGS absorber film prepared through chemical bath deposition method, photovoltaic conversion efficiency was reported to be higher than 19%. Such high efficiency has been reached with a CdS buffer layer processed in a wet chemical bath and the CdS has been found to be best suited as a buffer layer material. However, cadmium is toxic and has a negative effect on environment. Therefore, there have been many studies to find replacement materials for cadmium sulfide. The possible candidates for the cadmium free solar cells are ZnS, In2S3, ZnSe, InxSey. Among these materials, In2S3 is nontoxic and exhibits optical and electrical properties similar to those of CdS. Also, In2S3 thin film deposited by ALCVD using In(acac)3 and H2S was reported to be an n-type semiconductor and was found to properly function as a buffer layer for the heterojunction solar cells. For the preparation of In2S3 thin films without using toxic H2S gas, various single source precursors suitable to the MOCVD process are possible. Among them, the precursors containing dialkyldithiocarbamate ligands with non-symmetrical structure are interesting since they were found to have better thermal properties compared to symmetrical ones. In this work, two single source precursors, tris(N,Nethylbutyldithiocarbamato)indium(III) and tris(2-ethylpiperidinedithiocarbamato)indium(III) (designated as In(ebdtc)3 and In(epdtc)3, respectively) were synthesized with high purity and yield. Using them, In2S3 thin films were successfully grown on various substrates, such as glass, ITO glass, and CIGS film through MOCVD process. Experimental Details

Hydrogen states in CuInSe2—a μSR study

Implanted positive muons, used to mimic protons, are observed to form a diamagnetic state in the chalcopyrite semiconductor CuInSe2. A shift of the muon precession frequency is observed at a high transverse magnetic field (1600G) and is interpreted as being associated to the presence of a transient neutral state. A high charge or spin flip rate of the electron bound to the muon is suggested to be the cause for the absence of a hyperfine splitting, i.e., a direct signature of a neutral state. This observation is consistent with the presence of a hydrogen donor level close to or above the conduction band minimum.

Direct observation of the Cu2−xSe phase of Cu-rich epitaxial CuInSe2 grown on GaAs (001)

Cu 2−x Se is an important impurity phase of the ternary chalcopyrite semiconductor CuInSe2 associated with Cu/In composition ratios greater than unity. We have observed directly in a prototypical epitaxial system the formation of Cu2−xSe on Cu-rich CuInSe2 thin films epitaxially grown on GaAs (001). Atomic force microscopy measurements of the surface topology of as-grown films clearly show faceted rectangular crystallites with dimensions on the order of 100 nm. Cross-sectional transmission electron microscopy measurements of the Cu-rich CuInSe2 showed rectangular protrusions on the surface as well as wedge shaped facets in the CuInSe2 film. Two-dimensional reciprocal space x-ray mapping of the as-grown Cu-rich CuInSe2 showed the in-plane lattice constant of the Cu2−xSe phase to be partially strained to the CuInSe2 layer. The presence of the β phase of Cu2−xSe is also presented as an alternative explanation for Cu–Pt ordering reports in CuInSe2 that have appeared in the literature. Strain-related surface undulations observed only in Cu-rich CuInSe2 are also linked to the presence of this strained Cu2−xSe layer.

A Raman Scattering, Ion Channelling and Photoluminescence Study of Argon Ion Radiation Damage in Cu(Ga,In)Se2 - Dose Dependence and Dose Rate Effects

AbstractThe ternary chalcopyrite semiconductor CuInSe2 and related ternary compounds are promising materials for the production of high-efficiency thin film solar cells. In this paper we study the dose dependence of ion radiation damage produced by 30 keV and 80 keV Ar ions in single crystals and polycrystalline films of Cu(In,Ga)Se 2 over a wide dose range from 1012 to 1017 cm-2, using Raman spectroscopy and ion channeling measurements. For the first time, we also report on the dose rate dependence with a variation of the beam current density in the range 0.44 to 44 µcm-2. Even for low damage levels no significant dependence of the defect concentration or damage mechanism on the dose rate could be observed. From phonon correlation length considerations we estimate defect densities. They are in agreement with ion channeling data obtained in the 1015 to 1016 dose range, where the breakdown of the lattice structure occurs. In this dose range, the defect density is close to the concentration of implanted atoms. We conclude, that this high impurity concentration is responsible for the amorphization.

Room-Temperature, Electric Field-Induced Creation of Stable Devices in CulnSe 2 Crystals

Multiple-junction structures were formed, on a microscopic scale, at room temperature, by the application of a strong electric field across originally homogeneous crystals of the ternary chalcopyrite semiconductor CulnSe(2). After removal of the electric field, the structures were examined with electron beam-induced current microscopy and their current-voltage characteristics were measured. Bipolar transistor action was observed, indicating that sharp bulk junctions can form in this way at low ambient temperatures. The devices are stable under normal (low-voltage) operating conditions. Possible causes for this effect, including electromigration and electric field-assisted defect reactions, are suggested.

Comparison of properties of thin films of CuInSe2 and its alloys produced by evaporation, RF-sputtering and chemical spray pyrolysis

This paper summarizes a six-year research program aimed at preparation and characterization of thin films of the chalcopyrite semiconductor CuInSe2 suitable for photovoltaic solar cells and other semiconductors devices. The thin film deposition methods used were evaporation, flash evaporation, RF-sputtering and chemical spray pyrolysis. Problems with producing films of reproducible properties by these methods are discussed. Gaps in our knowledge of the dependence of the opto-electronic properties of CuInSe2 crystals and films on structural defects and other imperfections are pointed out.

Growth and structural characteristics of the chalcopyrite semiconductor CuInSe2

AbstractThe growth and structural characteristics of chalcopyrite semiconductor CuInSe2 have been investigated with particular emphasis on the photovoltaic behaviour of the CdS/CuInSe2 thin film heterojunction. It has been found that the structural phase of the CuInSe2 has an important bearing on the photovoltaic behaviour of the heterojunction. Thus the heterojunctions having the sphalerite type cubic CuInSe2 as one of its component have been found to possess better conversion effciency than those employing the chalcopyrite type tetragonal form of CuInSe2. Evidences and argument have been put forward to show that the better efficiency with sphalerite phase arises due to smaller lattice mismatch with CdS base. In addition to the type of structural phase, the state of order of CuInSe2 phase has been found to affect the performance of heterojunctions. The heterojunctions having the disordered sphalerite type CuInSe2 structure exhibits a much lower efficiency than those embodying the ordered CuInSe2 phase.