Silicon solar cell

Abstract

A high efficiency silicon solar cell (1) may be constructed by providing a two-stage drift field emitter (4) with a 1 micron thickness on a drift field base region (10) with a back surface field region (12). The stage (7) of the drift field emitter adjacent to the junction (8) is moderately doped from 10.sup.18 to 10.sup.16 atoms/cc adjacent the junction to minimize bandgap shrinkage and to maximize carrier lifetime while the stage of the emitter adjacent the surface is highly doped at 10.sup.19 atoms/cc to minimize sheet resistance. The drift field is aiding in both the emitter and base regions. The size of the base (10) is less than an effective diffusion length. There is a difference in doping level in the base depending on the conductivity type of the silicon. For n-conductivity type the base is doped 10.sup.13 atoms/cc at the pn junction, increasing to 10.sup.16 atoms/cc in the drift field region. For p-conductivity type the base is doped 10.sup.16 at the junction, increasing to 10.sup.18 atoms/cc in the drift field. A back surface field is provided adjacent the ohmic contact (3) on the part of the base remote from the junction by doping to 10.sup.20 to 10.sup.21 atoms/cc. A passivating antireflective layer (30) is added to the light incident surface. The 1 micron emitter region (4) contains a 0.1 to 0.2 .mu.m thick high conducting region (5) adjacent the antireflective coating (30) on the light incident surface and a drift field region (7) 0.3 to 0.9 .mu.m thick. The base region (10) has a drift field region (9) 20 to 100 .mu.m thick and the overall base region (10) is 50 to 450 .mu.m thick. The back surface field region (12) is 1 .mu.m thick.

Description