Small- and-large area Cu(In,Ga)Se2- based solar cells, as well as 20cm2 mini-modules are produced using a “baseline” approach that privileges process simplicity and statistical significance. High-quality devices are controllably obtained, as well as a 14.7% world record mini-module. Both “grided” and “conventional” mini-modules are produced and compared. A few processes from our research areas are presented as candidates for baseline integration. Among these, the examples of “fast” CIGS and “thin” CIGS are shown. For the latter, Ga-grading is involved and fill factors above 81% have been measured.

The high cost of photovoltaic (PV) energy has imposed extensive research efforts in order to provide alternatives to the conventional crystalline silicon (c-Si) PV technology. Thin film PV modules based on Cu(In,Ga)Se2 (CIGS) is considered one of the most promising alternatives for mass production of low-cost PV. In parallel to the development of new module technologies, there is an increasing interest for using concentrating optics in PV systems in order to increase radiation onto the modules. By replacing the relatively expensive PV absorbers with low-cost concentrators there is a potential reduction of overall system costs. The reflector types considered in this study are based on the compound parabolic concentrator (CPC) and the planar reflector. These are low-concentrating devices with concentration ratios of 1–4. With the CPC as well as the planar reflector, the illumination on the PV module will be non-uniform, with local light intensities that are considerably larger than the average 4 suns. For conventional c-Si modules, this is detrimental to module performance. It is demonstrated in the present work that modules based on thin film technology are better candidates for reflector applications. The principles of design and fabrication of CIGS thin film PV modules for low-concentrating systems are discussed, and experimental results from measurements of CIGS modules under concentrated illumination are evaluated.

Solar cells based on Cu(In,Ga)Se2 were prepared replacing the "standard buffer layer" CdS with a Inx(OH,S)y thin film. The film is deposited in a chemical bath (CBD) process using an aqueous solution containing InCl3 and thioacetamide. X-ray photoemission spectroscopy measurements were performed in order to characterize the growth kinetics and the chemical composition. The influence of different concentrations of InCl3 and thioacetamide in the solution on the electrical properties of the solar cells was studied by measuring the j-V characteristics and the spectral quantum efficiencies. Capacitance-voltage (C-V) measurements indicate that the high V∞ values of devices with the novel buffer layer are correlated with narrower space charge widths and higher effective carrier concentrations in the absorber materials. The achieved conversion efficiency of 15.7% (active area) using the cadmium free Inx(OH,S)y buffer demonstrates the potential of this process as an alternative to the standard chemical bath deposition of CdS.

A system for large-area deposition of Cu(In,Ga)Se2 by co-evaporation has been built and taken into operation. The system is designed after a patented approach, to use the kind of in-line process we are using in our small-area research work. Small-area laboratory cells have been made from CuInSe2 and Cu(In,Ga)Se2 films fabricated by the in-line process reaching active area efficiencies as high as 15.4% (CuInSe2) and 17.6% (Cu(In,Ga)Se2). Our Cu(In,Ga)Se2 module technology is described and the best results are reported. Best obtained aperture area efficiency for small modules (15 cm2) is 12.4% made on Cu(In,Ga)Se, films from our small-area deposition system. The large-area deposition system has produced CuInSe2 from which small-area cells with conversion efficiencies of 8.3% have been obtained so far

In an effort to find a process for deposition of the ZnO layer suitable for large scale fabrication of CIS cells the ALE method was investigated. In this study devices have been made with ZnO grown by ALE at temperatures which has been varied in the 125-200/spl deg/C interval. We find that high deposition temperatures have to be avoided in order not to degrade the open circuit voltage and fill factor of the devices. On the other hand the higher temperatures are needed to obtain high conductivity in the doped ZnO layer. In spite of that, devices with up to 14% efficiency were fabricated. Experiments where we omitted the CdS layer, normally used in CIS cells, were carried out. A promising result of 11% efficiency was obtained.

An important milestone in the development of photovoltaic thin-film solar cells is the achievement of 15% conversion efficiency. This letter describes the highest efficiency single junction thin-film cell reported to date. An active area efficiency of 14.8% is obtained with the cell structure n-ZnO/n-CdS/p-CuInSe2 deposited on a soda-lime glass substrate. The current achievements are due to improved properties of the CuInSe2 layer and the heterojunctions compared to previously reported results. The rate and substrate temperature profiles used during the coevaporation process yield a relatively large-grained material with very strong [112] orientation and low porosity. This results in reduced recombination rates, hence higher open circuit voltage and fill factor.

This paper reports results from experiments concerning the growth of CuInSe2 films on different substrate materials, uncoated, and coated with molybdenum. Specifically the effect on the structure, i.e. preferred orientation, of the polycrystalline films is investigated. It is found that soda-lime float glass results in the most oriented films and also that the highest solar cell conversion efficiency is obtained with devices made from such films. In another set of experiments the effect of various deposition conditions for the ZnO window layer is studied. It is found that optimum performance is not strongly dependent on the deposition process. The highly doped part of the window, ZnO:Al, has been replaced with ITO on some devices and a comparison is made. Finally, ZnO/CdS/CuInSe2 and ZnO/CdS/Cu(In,Ga)Se2 thin film devices exhibiting active area conversion efficiencies of 15.4% and 16.9%, respectively, are demonstrated

Major improvement of the performance of CuInSe/sub 2/-based heterojunctions has been obtained by replacing (Zn,Cd)S by a multilayer window consisting of ZnO and thin CdS buffer. The tradeoff between conductivity of the ZnO:Al and infrared free carrier absorption has been studied in connection with a n/sup +/n doping gradient. Bath chemistry of the CBD-CdS, (in particular different Cd-salts like CdCl/sub 2/, CdI/sub 2/, and CdSO/sub 4/) plays an important role in the resulting cell performances. XPS and UPS analyses have been carried out in order to investigate contaminations, coverage of the CuInSe/sub 2/ surface, and growth kinetics of the CdS layers grown in different baths. Optimized CdS thickness has been experimentally determined.< >

In a deposition system designed for coevaporation, the control of the individual evaporation rates is the crucial point. This paper describes a deposition system where the evaporation rates of three resistively heated elemental sources are controlled by utilizing a quadrupole mass spectrometer. The rate monitoring and control system is characterized for the case of CuInSe2 deposition, where it is shown that a precise control of the properties of the deposited film can be achieved. The results reported are of general interest, and neither restricted to three elements nor to the specific elements used in the case studied.