Johan Wennerberg

Cu(In,Ga)Se2-based thin-film photovoltaic modules optimized for long-term performance

Abstract In this contribution we give an overview of the mechanisms behind degradation of Cu(In,Ga)Se 2 -based modules. Based on the results from a detailed analysis of power losses in modules, prior to and after extended damp heat exposure, we discuss to what extent modules can be designed to achieve enhanced long-term performance. For conventional modules, we show that the stability can be improved by optimizing the interconnect and the front contact. Furthermore, we argue that gridded modules are better from a long-term performance point of view. A novel interconnect structure, specifically designed for long-term durability, is briefly discussed.

The change of the electronic properties of CIGS devices induced by the ‘damp heat’ treatment

Abstract The changes of the electronic properties of the absorber layer in the ZnO/CdS/Cu(In,Ga)Se2 photovoltaic devices induced by the ‘damp heat’ test have been investigated by use of junction capacitance techniques. Deep level transient spectroscopy and admittance spectroscopy have been employed for characterization of the bulk and interface levels in the absorber. Additional information on the transport mechanisms has been provided by the analysis of current–voltage characteristics. We conclude that the ‘damp heat’ treatment introduces deep electron traps, thus increasing the absorber compensation and decreasing Voc of the devices. The same states facilitate transport of carriers by means of trap-assisted tunneling, causing a decrease of the fill factor. OSe is a probable candidate for a defect introduced by the humidity test.

Design of concentrating elements with CIS thin-film solar cells for façade integration

A concentrating photovoltaic wall element, including Cu(In, Ga)Se-2-based modules, aluminum reflectors, and an insulation for building integration, has been developed and evaluated. The geometric concentration ratio of the system is about 3 x. However, the measured maximum electric power from the modules is only 1.9 times that of identical vertical modules without reflectors, due to optical losses and a decrease in fill-factor from 0.6 to 0.5 under concentrated light. The optical efficiency of the system is 76% at an effective solar height of 40degrees

A study of the influence of the Ga content on the long-term stability of Cu(In, Ga)Se2 thin film solar cells

A study of the influence of the Ga content on the long-term stability of Cu(In,Ga)Se2 thin film solar cells

Highly efficient Cu(In, Ga)Se2 mini-modules

In this contribution, we present results and the philosophy of our mini-module efforts. These efforts have achieved world record levels as well as a reproducible process. Various mini-module designs are tested using two different baseline Cu(In,Ga)Se2 deposition recipes. Gridded mini-modules achieve highest efficiencies and are much less demanding on the ZnO:Al top contact than their conventional counterpart. For all of the designs tested, our experimental results are in the order of the expectations from our modeling. Gridded modules can achieve efficiency levels very close to those of the cells.

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.

Design of Grided Cu(In,Ga)Se2 Thin Film PV Modules

Abstract Results from modeling designs of Cu(In,Ga)Se2 thin-film PV modules show that grided modules, at standard test conditions as well as at low-concentrated light, exhibit significantly improved performance when compared with conventional designs. It is further discussed that a grided design is advantageous from a synthesis and manufacturing point of view, since it provides higher front contact process tolerance and throughput as well as improved degrees of freedom of the module geometry.

Optoelectronic images of polycrystalline thin-film solar cells based on CuInSe2 and CuInGaSe2 obtained by laser scanning

The laser scanning technique was used to obtain two-and three-dimensional optoelectronic images of polycrystalline solar cells based on thin films of CuInSe2 and CuInGaSe2. Topograms obtained with the aid of the laser-beam-induced current reveal microregions with reduced photovoltaic efficiency and provide a detailed picture of the distribution of hidden inhomogeneities over the entire active surface of the solar cell. Gradation of the microdefects with intensity and size was achieved by post-experimental graphic and false-color processing of the obtained three-dimensional images.

Computer modeling and visualization of hidden defects in thin film solar cells on CuInSe2 and Cu(In,Ga)Se2

The laser scanning technique was used to realize two- and three-dimensional optoelectronic images of polycrystalline solar cells based on thin films of CuInSe2 and CuInGaSe2. Topograms obtained with the aid of the laser-beam-induced current and computer modeling reveal microregions with reduced photovoltaic efficiency and provide a detailed picture of distribution of hidden inhomogeneities over the entire active surface of the solar cells. Gradation of the microdefects with intensity and size has been achieved using post-experimental graphic and false-color processing of the obtained three-dimensional images.