Roland Trassl

Industrial PVD metallization for high efficiency crystalline silicon solar cells

In this paper we present first results concerning different thermal evaporation processes for thin aluminum layers, which are carried out on a pilot system with a throughput of up to 540 wafers/h (156×156 mm2). To qualify the processes the deposited aluminum layers were evaluated with respect to homogeneity and conductivity. Additionally the effect of the different processes on the passivation quality of a thermally grown 100 nm thick SiO2 was analyzed by means of lifetime measurements, indicating a negligible effect of the conducted process variations on the passivation quality. Finally high-efficiency silicon solar cells were prepared to determine the overall potential and to compare it with an electron beam (e-gun) evaporation process, which is used as a standard process in our laboratory. An efficiency of up to 21% was achieved by the high deposition rate technique performing at least as well as our standard high efficiency process.

Simultaneous gettering and emitter formation in multicrystalline-Si wafers by annealing phosphorus doped amorphous silicon compounds

We demonstrate gettering of metal impurities in p-type multicrystalline silicon (mc-Si) wafers by annealing wafers that are surface passivated by double layers of amorphous silicon-based compounds acting as gettering sites. As inner layer we use a phosphorus-doped amorphous silicon-carbon-nitrogen alloy, providing surface passivation and acting as dopant source for the emitter formation during subsequent anneal. The outer layer is silicon nitride with antireflective properties. Anneals are done at 750, 800, and 850 °C for 30 and 60 min. The gettering effect is as good as for a conventional POCl3 diffusion followed by extended gettering at low temperature, and it is weakly influenced by the temperature step chosen. In the range explored, the sheet resistances of the emitters and the junction depths lay between 3000 to 60 Ω/sq. and 100–300 nm, respectively.