A mask-less crystalline silicon solar cell was made by using a surface texturing technique coupled with an oblique aluminum evaporation. To achieve this, trenches with a steep sidewall are mechanically grooved into the bulk silicon using the KS 775 Wafer Saw. More importantly, metal evaporation with the CVC evaporator at angles near parallel to the wafer surface allows deposition to occur along the side of the trenches creating the self-aligning front metal contacts. Of the four solar cells that made it through the processing, only one solar cell showed diode like 1-V characteristics. The dark conditions shows a diode 1-V where current doesn’t flow with a negative applied voltage and in the forward applied voltage, there is a turn on voltage around 0.6V, typical of a silicon diode. This is followed by an exponential gain in current. The n value of the diode is under dark conditions is 1.7. Under illuminated conditions, the I-V curve shows a dramatic negative current for voltages below 0.25V. This isn’t the I-V curve of a solar cell but it does show that this device is light sensitive. The other three solar cells made are resistors with resistances of 4 Ω, 2 Ω and 19.2 Ω for wafers 3, 4 and 5 respectively. The shorts on the solar cells are due to a nonuniformly coated N-250 spin on glass (SOG) for the n+ layer on the p type wafer. Air pockets remained in the trenches and kept certain spots on the wafer surface to remain p. When the Al front contacts and bus paste are applied to the solar cells, it creates the p-n junction shorts. This was confirmed by breaking wafer 3 into smaller pieces where one of the pieces had a uniform n+ layer that showed I-V curves of a diode.
Chan, C K. and Pearson, R E.
"Mask-Less Crystalline Silicon Solar Cell (May 2009),"
Journal of the Microelectronic Engineering Conference: Vol. 18
, Article 3.
Available at: http://scholarworks.rit.edu/ritamec/vol18/iss1/3