Improving n(+)pp(+) single crystalline silicon solar cells by long high temperature Al annealing

In this work, we show that solar cells made on solar grade silicon can be i mproved by annealing them at high temperatures (800 degreesC) after the alu minum at the back is evaporated. This improvement is larger for longer anne aling times. Both the short circuit current (Isc) and the open circuit volt age (Voc) increase due to an increase of the base minority carrier diffusio n length and a reduction of dark current, respectively. This effect may be due to "gettering" of metallic impurities and precipitates at die bulk and junction regions of the cells. For this high annealing temperature we obser ved that the increase of Jsc tends to saturate after 60 minutes, while Voc continues increasing for annealing times above 150 minutes.