High voltage amorphous silicon solar cells by hot-wire chemical vapor deposition

We have achieved the best open-circuit voltage (V-oc = 0.94 V) to-date in hydrogenated amorphous silicon (a-Si:H) photovoltaic cells deposited entirely by hot-wire chemical vapor deposition. The fill factor (FF = 0.74) remained high. and a current density of 8-9 mA/cm(2) with about 1800 Angstrom i-layer was obtained in our n-i-p cells on untextured stainless-steel substrates. The V-oc improvement of about 60 mV in compared to our previous best V-oc was obtained by incorporating materials grown with H-dilution close to the phase transition from amorphous to microcrystalline silicon in the i-layer and at the i-p interface. A low substrate temperature of 150 degreesC for the i-layer was also essential, most likely to widen the bandgap of the i-layer. A brief atomic H-treatment after grown the i-layer increases the V-oc further by improving the p-i interface. The last 60 A of the i-layer before p-layer is extremely close to the transition to microcrystallinity, though it remains mainly amorphous. Our p-layers are also close to the phase transition.