Jonas Hedström

A novel cadmium free buffer layer for Cu(In,Ga)Se2 based solar cells

Abstract Solar cells based on Cu(In,Ga)Se 2 were prepared replacing the “standard buffer layer” CdS with a In x (OH,S) y thin film. The film is deposited in a chemical bath (CBD) process using an aqueous solution containing InCl 3 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 InCl 3 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 In x (OH,S) y buffer demonstrates the potential of this process as an alternative to the standard chemical bath deposition of CdS.

Baseline Cu(In, Ga)Se2 device production : Control and statistical significance

Small- and-large area Cu(In,Ga)Se 2 - based solar cells, as well as 20 cm 2 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.

Thin film PV modules for low-concentrating systems

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.

Coevaporation with a rate control system based on a quadrupole mass spectrometer

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.