Radiation-induced defects in thin Cu(In,Ga)Se2 films on exposure to high-energy electron irradiation

Abstract

UDC 621.378At 4.2 K, the photoluminescence spectra of Cu(In,Ga)Se 2 films irradiated by electrons with an energy of 5 MeV displayed the 0.93-and 0.79-eV bands that owe their origin to the radiative recombination of nonequilibrium charge carriers on radiation-induced defects. The position of the energy levels of the defects is determined and their nature is discussed.Introduction. Creation of high-efficiency solar elements based on Cu(In,Ga)Se 2 (CIGS) is a topical scientifictechnical problem of contemporary semiconductor photoenergetics [1,2]. The value of the efficiency currently achieved for the solar elements based on CIGS is about 19.2% [3]. Here, particular attention is being given to the creation of radiation-resistant semiconductor photoconverters capable of functioning reliably and for a long time under the conditions of exposure to penetrating radiation, in particular, in outer space [4,5]. The most common method of determining the criteria of radiation resistance of CIGS solar elements and films under the ground-based conditions is to study the degradation of their parameters and physical properties on exposure to high-energy protons and electrons [6,7].In the present work, we describe experiments carried out to establish the nature of radiation-induced defects on irradiation by high-energy electrons in CIGS films commonly used in serial manufacture of solar elements with an efficiency of about 12-14% [8]. For the first time, to determine the influence of electrons on CIGS compounds, a nondestructive method (luminescence) is used, which allows one to register the formation of energy levels in the energy gap and to perform the identification of the type of defects formed on the atomic level.Experimental. We investigated thin (,1 µm) CIGS films, with p-type conductivity, which were grown directly on glass substrates or on a thin layer of molybdenum preliminarily sputtered onto glass. The elemental composition of the films was determined using x-ray spectral analysis and scanning Auger-electron spectroscopy. Exposure to electrons with an energy of 5 MeV was performed on a linear accelerator by a dose of about 10 18 cm -2 at a temperature less than 50 o C. The electron flux density was about 2⋅10 12 cm -2 ⋅sec -1 . The absorption spectra in the 0.2-3.0-µm region were registered on a Cary-500 UV-VIS-NIR two-beam spectrometer (Varian, USA), the photoluminescence spectra were obtained with the aid of an MDP-23U grating monochromator with the focal length of a mirror objective

Effects of irradiation of ZnO/CdS/Cu2ZnSnSe4/Mo/glass solar cells by 10 MeV electrons on photoluminescence spectra

“…Irradiation with MeV electrons, carried out at low temperatures, induces new bands in the PL spectra of such binary semiconductors as ZnSe [21], ZnO [22] and GaN [23]. MeV electrons also induce new bands in the PL spectra of CuInSe 2 [24] and Cu(In,Ga) Se 2 [25].…”

Surface Composition of CIS Compound Affected by Xe⁺ Irradiation

“…As it is shown in Refs. [17,19], the defects in CIS films are related with In and Se vacancy or with the In substitution by Cu atoms that leads to the copper concentration increase. As a result of the films irradiation with the 40 keV Xe + ions (fluence 1 × 10 14 cm −2 ) a defect formation enhancement occurs with the copper concentration increase to 46 at.% (Table II).…”

“…Besides, defect formation in this layer by both deposition and operation can result in degradation as well as solar elements efficiency rise [10][11][12][13][14][15][16][17][18][19]. This indicates insufficient investigation of defect creation in the CuInSe 2 films system and poor knowledge of these processes that does not allow to realize CIS potential in full.…”

Influence of Chemical Composition Heterogeneity on the Spectral Position of the Fundamental Absorption Edge of Cu(In, Ga)Se2 Solid Solutions

“…The experiments showed that the ratio of elements in the CIGS thin fi lms varied from Ga/(Ga + In) ~ 0.28 on the surface to ~0.58 near the glass substrate. It is noteworthy that heterogeneous distributions of In and Ga with a preferential increase of the Ga concentration near the glass substrate or a contact layer of Mo on glass were previously observed [7,[14][15][16]. This must be considered when analyzing the physical properties of CIGS solid solutions.…”