Drawing the Most Power From Low-Cost Single-Well 1-mm2 CMOS Photovoltaic Cells

Photovoltaic (PV) cells can generate 100x more power from light than other transducers can from motion, radiation, and heat. Although custom multijunction nonsilicon and multiwell complementary metal-oxide-semiconductor (CMOS) cells output more power, single-well process technologies cost less. Amorphous cells cost even less but output less power. However, with only a small window of light available, tiny CMOS cells output little. This brief explores and proposes open-terminal singlewell CMOS PV cell configurations that output more power than competing low-cost CMOS cells in literature. Measurements with 0.35-mu m 1 x 1-mm(2) single-well CMOS cells show that deeper and lighter doped junctions generate higher power than shallower junctions, and double-junction configurations output even higher power. This is why sunlight on N+ in P substrate and N well in P substrate cells outputs 6 and 98 mu W and on shorted and open-terminal P+ in N well in P substrate structures outputs 132 mu W. Opening the P+ terminal outputs even more power because P+ metal, which blocks light, is no longer necessary.