Development of High Performance Industrial TCO Glass for Very Large Area a-Si:H PV Modules

Abstract

The European project HELATHIS, executed by the five project partners signing this article, is dedicated to the improvement of the efficiency of very large area (5.7m2) silicon thin film photovoltaic (PV) modules. Optical confinement has been identified by the project partners as a major source for efficiency improvement of thin film silicon PV modules. One reason of the performance gap between highly efficient laboratory solar cells and industrial modules is the poorer electrical and optical performance of the industrial TCO-covered front glass substrate (TCO glass) which is investigated in this work. The glass substrate in industrial PV modules is about 3 times thicker than in laboratory solar cells where frequently Asahi U-type TCO glass (about 1 mm thick) is used. Therefore, the glass quality has an important impact on the transmission of industrial TCO glass. Reducing the iron-content in the float glass substrate increases the integrated transmission in the wavelength range from 400-800nm by nearly 2%. The electrical properties, namely the electrical carrier mobility, of the industrial TCO layer of AGC has been increased by about 15% by improving the industrial deposition process, resulting in a thinner TCO layer with higher transmission by maintaining the sheet resistance of about 9-10 /sq. Combining both developments the integrated transmission of industrial TCO glass has been increased by more than 2%. The TCO layer properties of Asahi U-type and standard industrial TCO glass (AGC AN10) have been investigated by SEM, AFM, XRD and ARS, showing that the Asahi U TCO scatters red light more effectively into larger angles.