INTEGRATION OF SCREEN-PRINTING AND RAPID THERMAL-PROCESSING TECHNOLOGIES FOR SILICON SOLAR-CELL FABRICATION

For the first time, the potentially cost-effective technologies of rap id thermal processing (RTP) and screen-printing (SP) have been combine d into a single process sequence to achieve solar cell efficiencies as high as 14.7% on 0.2 Omega-cm FZ and 14.8% on 3 Omega-cm Ct silicon. These results were achieved without application of a nonhomogeneous (s elective) emitter, texturing, or oxide passivation, By tailoring the R TP thermal cycles for emitter diffusion and firing of the screen-print ed silver contacts, fill factor values >0.79 were realized on emitters with a sheet resistance (rho(s)) of similar to 20 Omega/square and gr id shading <6%, Such high fill factors clearly demonstrate that screen -printed contacts can be fired on extremely shallow RTP emitters (x(j) = 0.25 - 0.3 mu m) without shunting cells, IQE analysis depicts a str ong preference for shallow emitter junction depths to achieve optimal short wavelength response of these unpassivated emitters, In some case s, front contacts were printed through plasma enhanced chemical vapor deposited (PECVD) SiN/SiO2 dielectrics which prevented the shunting of shallow emitters by serving as partial barriers minimizing the diffus ion of metallic species from the contacts. The firing of screen-printe d contacts through these PECVD films, achieved the multiple purposes o f contact formation, efficient front surface passivation due to anneal ing of the SW, and high quality antireflection (AR), Research is prese ntly underway to further optimize the RTP emitter design for screen-pr inting and develop techniques for implementing selective emitter and o xide passivation technologies for higher efficiency cells.