A study on the microscopical and macroscopical effects of hydrogenation on the performance of multicrystalline solar cells

The grains in the multicrystalline materials used nowadays are typically in the order of a mm or more. In the present study the improvement of different materials (Eurosolare material and EMC material from Sumitomo Sitix) is studied. The method of hydrogenation used consists of a hydrogenation in an RF-plasma. The treatment is from the front or back side of the substrate. The beneficial effect of hydrogenation is illustrated by I-V-measurements under AM1.5 illumination, dark I-V measurements and extraction of minority carrier lifetime by the microwave-detected photoconductive decay method. The measurement on the full solar cell reveals only macroscopic and hence lumped consequences of the hydrogenation. Additional insight was gained from measurements on small mesa-type diodes. In this way we can discriminate between diodes with a grain boundary running through the active device and devices fully contained within one grain. This allows one to split the effects of the hydrogenation on the grain boundaries and the intra-grain defects. Dark I-V-measurements and deep-level transient spectroscopy (DLTS) were used to characterize the diodes in the Eurosolare material. The DLTS-spectra revealed a broad band for the diodes with a grain boundary running through them. This peak completely disappeared on samples which received a direct H-plasma treatment from the front side.