Preparation and analysis of properties of thin-film Cu (In, X) Se2 solar cells prepared by methods of plasma deposition and spray sputtering


Thin-film solar cells whose absorption layer consists of Cu (In, X) Se2 chalcopyrites (where X = Ga, In, B, with the most common substituent being Ga and chalcopyrite being referred to as CIGS) have been extensively studied for more than 20 years and are among the most promising candidates for alternative energy sources in the very near future. This is mainly due to the physical properties of said chalcopyrite. Among the most important are the variability of the band gap in a wide interval around the optimal value of 1.4 eV and a high value of the absorption coefficient (more than 105 cm-1), which in comparison with silicon cells extremely reduces the thickness of the absorption layer to less than 2 m. Modern research on CIGS articles goes in two main directions:

1) Maximizing efficiency (The current world record announced on August 23, 2010 by the German Solar Energy Institute (Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg) is 20.3%.) 2) Minimization of production costs (most often through cheap non-vacuum deposition of nanocrystalline layers even at the cost of significantly lower efficiency)

The most common laboratory methods used to prepare CIGS solar cells include plasma deposition or electrodeposition of Cu, In and Ga precursors and their subsequent selenization or sulfurization, as well as coevaporation of Cu, In, Ga, Se elements on a preheated substrate, or methods of chemical vapor deposition. (CVD). The heterojunction itself and the entire solar cell is then completed by depositing a thin layer of cadmium sulfide CdS (using CBD) and a layer of zinc oxide ZnO doped with aluminum. The efficiency of the synthesized cell strongly depends on the production technology and the quality of the individual layers is related to it. The laboratory of the Department of Low-Temperature Plasma of the Institute of Physics of the ASCR has unique devices enabling the deposition of thin-film solar cells by technologies that have not been tested yet. Similarly, the laboratory of the collaborating workplace of the University of Nebraska in Kearney presented in 2010 a unique method of CIGS deposition using RTA (rapid thermal annealing) from the multilayer structure of CuIn1-xGaxS2 / Se nanocrystals prepared by CBD. The submitted project will therefore study the deposition of individual layers and the production of CIGS and CIAS solar cells in two main ways:

1) Deposition of metal precursors for CuIn1-xGaxSe2 and CuIn1-xAlxSe2 absorption layers by pulsed magnetron sputtering in DC, RF and HIPIMS (High Power Impulse Magnetron Sputtering) modes and deposition by discharge in a hollow cathode or by a system of two or more hollow cathodes ( with the same excitation as in the previous case). The collaborating laboratory in the USA will perform the selenization of precursors, the addition of CdS and the characterization of already finished layers. The article will be completed in Prague by the deposition of ZnO and ZnO: Al. The aim of this procedure is to achieve higher efficiency for cells sputtered in the HIPIMS mode, which would correspond to both theoretical expectations and the results of preliminary experiments. 2) Deposition of nanocrystalline CIGS layers by spray sputtering of chemical solution prepared by CBD method, deposition of CdS by CBD method (none part requires vacuum, will be performed in USA) and subsequently deposition of ZnO and ZnO: Al by atmospheric torch discharge (does not require vacuum, will be performed in CR). The aim of this procedure is to create a functional prototype of a solar cell created exclusively by technologies that do not require vacuum and to optimize deposition conditions in order to maximize efficiency.

In the case of the first procedure, the properties of the deposition plasma will be studied directly during the deposition using optical emission spectroscopy (OES), time-resolved laser absorption spectroscopy, Langmuir probe, SEMION ion analyzer and other advanced techniques. Attention will be focused mainly on the comparison of the quality of individual layers deposited in different ways and their influence on the overall efficiency of the solar cell. The individual layers will be analyzed by a number of sophisticated methods, mainly through X-ray diffraction (XRD), Raman spectroscopy, optical ellipsometry, scanning electron microscopy (SEM), atomic force microscopy (AFM), UV / VIS absorption spectroscopy, profilometry, RBS, XPS, GDOES and others. . The measured values ​​of technological plasma parameters, measured parameters of layers and the overall efficiency of the solar cell will be mutually correlated and the influence of individual parameters on the properties of the entire multilayer structure will be monitored.