Abstract
Cu(In, Al)Se2 thin films were prepared by electrodeposition from the aqueous solution consisting of CuCl2, InCl3, AlCl3 and SeO2 onto ITO coated glass substrates. The as-deposited films were annealed under vacuum for 30 min at temperature ranging between 200°C and 400°C. The structural, composition, morphology, optical band gap and electrical resistivity of elaborated thin films were studied, respectively using x-ray diffraction, energy dispersive analysis of x-ray, scanning electron microscopy, UV spectrophotometer and four-point probe method. The lattice constant and structural parameters viz. crystallite size, dislocation density and strain of the films were also calculated. After vacuum annealing, x-ray diffraction results revealed that all films were polycrystalline in nature and exhibit chalcopyrite structure with (112) as preferred orientation. The film annealed at 350°C showed the coexistence of CIASe and InSe phases. The average crystallite size increases linearly with annealing temperature, reaching a maximum value for 350°C. The films show a direct allowed band gap which increases from 1.59 to 1.78 eV with annealing temperature. We have also found that the electrical resistivity of films is controlled by the carrier concentration rather than by their mobility.
Highlights
One of the main challenges in photovoltaic research is the development of lower cost and higher conversion efficiency devices
Fabrication of thin film tandem cell gets relatively simplified if the desired band gap semiconductor absorber layers for the top and bottom cells can be obtained from a single ternary or quaternary alloy system by varying the alloy composition suitably [1]
We found that the pace of the electrical resistivity according to the annealing temperature is similar to that of the crystallite size, we inferred that the films resistivity is controlled by the carrier concentration rather than by their mobility
Summary
One of the main challenges in photovoltaic research is the development of lower cost and higher conversion efficiency devices. This primary objective can be achieved by using tandem solar cell structures. Cu(In, Al)Se2, abbreviated as CIASe, is considered as an quaternary interesting absorber material for the wide band gap cell in the thin film tandem structures, because it requires smaller relative alloy concentration than gallium (Cu(In, Ga)Se2) or sulphur (CuIn(S, Se)2) alloys to. The conversion efficiency has already exceeded 16.9% using CIASe material as absorber layer in solar cell [5]. The relationship between the properties of the Cu(In, Al)Se2 films and the annealing temperature is studied
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