We are optimising the plasma enhanced chemical vapour deposition (PECVD) conditions for amorphous silicon-based films to achieve the best level of surface passivation of silicon wafers. to facilitate the subsequent development of high efficiency thin silicon solar cells. Surface recombination velocity (SRV) is used to describe the level of passivation Surface recombination in solar cells should be kept as low as possible as it leads to a loss of light-generated charge carriers and thus to a reduction in cell efficiency. Non-saturated bonds on the surface of a semiconductor are the source of a large density of defects, where recombination via defects as described by the Shockley-Read-Hall , theory takes place. For example, a crystalline silicon solar cell with a thickness of 150 µm, the SRV has to be smaller than 750 cm/s for an efficiency exceeding 18 %, or below 100 cm/s to get close to 19 % efficiency.
The currently used system is connected to various gases with flow rates ranging from 1 – 100 sccm and substrate temperatures
up to 350 °C thus enabling us to grow a-Si:H, SiNx or SiC.The HWU PECVD system can be operated with either a microwave or radio-frequency (RF) power supply.
Our aim is fabricate a 150 µm thin crystalline silicon solar cell with Laser grooved buried contacts on the front,
laser fired rear contacts and an efficiency of 20 %. This cell is developed within the DTI project HIGHPOINT together with our partner NaReC.