EDGE PASSIVATION OF HETEROJUNCTION SOLAR CELLS FOR RESEARCH PURPOSES

Silicon heterojunction (HJ) solar cell is one of the leading technologies for single junction photovoltaic devices and it could be successfully integrated into a silicon based multijunction solar device, in conjunction with a large band gap cell. To be used as a bottom cell, the HJ device needs to adapt to the current technology for top cells, which are typically far less mature and characterized by smaller areas. However, if the HJ device is cut from a finished larger cell, the original edge passivation gets lost, causing the introduction of surface recombination paths and an overall decrease of the device performance. In this context, the development of a proper edge passivation procedure to be applied to high quality HJ solar cells becomes of major importance. We tried two different strategies of edge passivation based either on wet processes, such as the mesa etching of the device, or plasma treatment of the vertical edges. The latter consisting in the deposition of 1-10 nm of hydrogenated amorphous Si on the edges. In order to characterize the recombination losses and quantify the effect of different passivations, we did current-voltage measurements in light and dark conditions and quasisteady-state photoconductivity measurements.