Comparison of Front and Back Surface Passivation Schemes for Silicon Solar Cells

Presented at the 2nd World Conference on Photovoltaic Solar Energy Conversion; Vienna, Austria; July 6-10, 1998.This work presents a comprehensive study on fast, low-cost methods for the electronic passivation of the phosphorus-diffused front surface and the non-diffused p-type rear surface of crystalline Si solar cells. Titanium dioxide is compared with rapidly-grown thermal oxide (RTO) and PECVD silicon nitrides from three different laboratories. Double layers of RTO and Ti02 or SiN are also investigated. We demonstrate that SiN and RTO single layers can provide very good passivation on both the front and back surface of solar cells. It is also shown that double layers consisting of a thin RTO film and silicon nitride can improve the passivation quality of most SiN layers, and enhance the stability under thermal treatment. With the proper choice of RTO, SiN, and thermal treatment, excellent surface recombination velocities on the back as well as very low emitter saturation currents can he reached using these fast, industrially feasible methods. All films used also provide or are compatible with a good antireflection coating of the cell surface