Silizium-Flüssigphasenepitaxie (LPE) : dünne Schichten auf kostengünstigen Si-Substraten und neuartige Metallisierungskonzepte für photovoltaische Anwendungen

Abstract

Within this work the epitaxial solution growth of thin silicon (Si)-layers on cost effective<br />Si-substrates was investigated. The properties of these layers were adapted to the processing<br />of thin film solar cells. This technology could help to decrease the shortage of pure Si for<br />photovoltaic applications in the future.<br /><br />In the course of this study a broad spectrum of growth parameters were varied in order to<br />investigate their influence on the quality of the epitaxial layer. It was shown that the use of<br />the melt back technique is necessary and in addition the growth rate has to be lower than<br />0.5 µm/min to obtain continuous Si-layers.<br />In order to still enable an industrial application of the LPE technique regarding such low growth<br />rates, a new stack procedure was applied where several substrates were dipped into the growth<br />solution at once. Using thin layers grown with this technique the efficiency of industrially<br />processed solar cells was essentially improved compared to fast, single grown layers. Open<br />circuit voltages of nearly 600 mV and fill factors of up to 76.4 % led to a record efficiency<br />of 10.0 %. Simulations showed that efficiencies above 13 % are possible.<br /><br />During LPE experiments with microscopically grooved substrates an interesting observation<br />led to the idea to take advantage of the wetting properties of the tin solvent in order to metallise<br />the solar cell. This novel contacting technique is based on the so called Buried Contact Solar<br />Cell (BCSC) technology. The cells showed excellent contact properties. Finger resistances of<br />500 mOhm/cm, specific contact resistances in the range of 0.1 mOhm-cm2 and fill factors of up to<br />78 % are comparable with parameters obtained by industrial BCSCs.