Nicholas Allsop

Deposition of In2S3 on Cu(In,Ga)(S,Se)2 thin film solar cell absorbers by spray ion layer gas reaction: Evidence of strong interfacial diffusion

Recently, Cd-free Cu(In,Ga)(S,Se)2-based “CIGSSe” thin film solar cells with a nominal In2S3 buffer layer deposited by the spray ion layer gas reaction technique resulted in photovoltaic performances comparable to that of CdS buffered references. In the past it was argued that diffusion processes across the In2S3∕CIGSSe interface play a significant role for the device quality. Investigating the interface formation by using x-ray photoelectron spectroscopy, the authors were able to confirm a strong interfacial diffusion involving Cu and Na from the CIGSSe.

Three-dimensional simulations of a thin film heterojunction solar cell with a point contact/defect passivation structure at the heterointerface

Thin film heterojunction solar cells such as those based on the chalcopyrites or amorphous silicon are often limited by interface recombination at the active heterointerface. A new strategy to overcome this limitation is described, replacing the conventional wider band gap contact material with a combination of a passivation layer plus the conventional contact in a point contact type structure. This is similar to the established method to minimize rear contact recombination in crystalline silicon solar cells. Here point contacts at the heterointerface of a CuInS2 based solar cell are modeled using the WIAS-TeSCA code. The importance of the donor defect energy level at the absorber/passivation interface is shown, and a way to improve the cell efficiency by >25% (relative) is outlined.

Up-scaling ILGAR In 2 S 3 buffer layers production for chalcopyrite solar modules

Indium sulfide buffer layers produced by the spray ion-layer-gas-reaction (ILGAR) have already been shown to be a suitable replacement for the standard CdS layer in chalcopyrite based thin film solar cells. However, to date, all of the results have been shown on small area solar cells. Here we demonstrate both the up-scaling of the spray ILGAR process for the first time and show results for mini-modules based on Cu(In,Ga)(Se,S)2 (CIGSSe) absorbers from the AVANCIS pilot line. The mini-module efficiencies reach 12.4% and damp heat stability is comparable to CdS buffered references. Analysis of the modules by thermography shows a strong correlation between homogeneity and module performance. This preliminary up-scaled 10 × 10 cm deposition chamber paved the way for further large scale development. This includes a tape coater, built in-house, a 30 × 30 cm machine under construction with STANGL semiconductor equipment AG and a roll-to-roll ILGAR machine, which is currently part of the pilot production line operating at CIS-Solartechnik in Hamburg.

Non-vacuum chalcopyrite solar cell absorbers: The Spray-ILGAR approach

In this report, solar cells based on CuInS2 absorber films, which were prepared by the Spray-ILGAR method, are presented for the first time. All solar cells had a glass/Mo/CuInS2/CdS/i-ZnO/n-ZnO/Ni-Al structure. Solar cells were produced from Spray-ILGAR CuInS2 absorber films using various deposition parameters. To date, a maximum efficiency of 4.1 % has been achieved. The CuInS2 absorber films consist of two layers of different crystalline quality. The origin as well as the influence of this structure on the photovoltaic performance is discussed. Therefore, scanning electron microscopy and Raman spectroscopy were applied, in order to characterize the Spray-ILGAR CuInS2 absorber films.

Towards Lower Deposition Temperatures of Spray Deposited ZnO Films

Highly transparent, conductive ZnO:Al doped films have been deposited by a non-vacuum spray deposition method. At substrate temperatures above 400C we attain resistivites of 5x10-3Ohmcm and free charge carrier concentrations of 10-20cm -3 . ZnO film growth and quality are sensitive to the precursor solution. For a non-vacuum process the properties of the films are excellent. The challenge is to lower the deposition temperature to a maximum of 250C to be useful for Cu(In, Ga)(S, Se) 2 solar cells and yet maintain the ZnO film quality and conductivity. As the deposition temperature decreases the resistivity of the ZnO drastically increases yet is conducting enough to be used undoped as the intrinsic ZnO layer. This is particularly relevant as the deposition technique is readily up-scalable to roll to roll coating processes.

Solar Cells prepared with Spray-ILGAR Indium Sulfide buffer layers on Cu(In,Ga)Se 2 Absorbers

Indium sulfide buffer layers deposited by the Spray-Ion Layer Gas Reaction (Spray-ILGAR) technique have recently been used with Cu(In,Ga)(S,Se) 2 absorbers giving cells with an efficiency equal to the cadmium sulfide references. In this paper we show the first results from cells prepared with Cu(In,Ga)Se 2 absorbers (sulfur free). These cells reach an efficiency of 13.1% which remains slightly below the efficiency of the cadmium sulfide reference. However, temperature dependant current-voltage measurements reveal that the activation energy of the dominant recombination mechanism remains unchanged from the cadmium sulfide buffered cells indicating that recombination remains within the space charge region.