Polycrystalline silicon thin-film solar cells prepared by layered laser crystallization with 540 mV open circuit voltage

Abstract

Polycrystalline silicon thin film solar cells on a glass substrate are investigated. The solar cell layer structure was generated by a two-step process in which first a 100–600nm thin seed layer is formed by diode laser crystallization of electron beam evaporated amorphous silicon. In a second step this layer is epitaxially thickened to 2–3.5μm by layered laser crystallization. In this process further amorphous silicon is deposited and in situ repeatedly is irradiated by excimer laser pulses. The polycrystalline layer consists of grains several hundreds of microns long and several tens of microns wide and it contains a p+–p–n+ doping profile. After deposition a rapid thermal annealing and hydrogen passivation steps follow. The back and front contacts are prepared after mesa structuring. The influence of the seed layer thickness on the solar cell performance was investigated. In addition, the absorber contamination due to the background pressure during absorber deposition and its influence on the short circuit current density was investigated. The best parameters reached for various solar cells are 540mV open circuit voltage, 20.3mA/cm2 short circuit current density (without light trapping), 75% fill factor, and 5.2% efficiency.