Assessment of intrinsic-layer growth temperature to high-deposition-rate a-Si:H n-i-p solar cells deposited by hot-wire CVD

We report progress in hydrogenated amorphous silicon n-i-p solar cells with the i-layer grown by the hot-wire chemical vapor deposition technique. Early research showed that we grew device-quality materials with low saturated defect density (2 x 10(16)/cm(3)), high initial ambipolar diffusion length (similar to 2000 Angstrom) and low hydrogen content (<1%). One of the major barriers to implementing this material into solar cells is the high substrate temperature required (>400 degrees C). We re-assess the effects of low substrate temperature on the property of the films and the performance of the solar cells as an alternative avenue to solving this problem. We find that the material grown at 300 degrees C can have similar values of saturated defect density and ambipolar diffusion length as the one grown greater than 400 degrees C. We also study the effect of i-layer substrate temperature ranging from 280 degrees to 440 degrees C for n-i-p solar cells. We now consistently grow devices with Fill Factor (FF) greater than 0.66, with the best close to 0.70 at lower substrate temperature. A collaboration with United Solar System, in where they grew the p-layer and top contact, produced devices with initial efficiencies as high as 9.8%. We produce n-i-p solar cells with initial efficiencies as high as 8% when we grow all the hydrogenated amorphous silicon and top contact layers. All these i-layers are grown at deposition rates of 16 to 18 Angstrom/sec. We need to further improve our p-layer and transparent conductor layer to equal the collaborative cell efficiency. We also report light-soaking results of these devices.