Grain Boundary Effects on the Electrical Behavior of Al-Poly-Si Schottky-Barrier Solar Cells

Schottky-barrier diodes using aluminum on p-type polycrystalline silicon have been fabricated. The contrast of the orientation of neighboring grains is observed after chemical etching of the surface. Comparing the surface morphology of the substrate with the electronic behavior of the Schottky diode, we are able to identify the influence of grain boundaries. It is found that the low-angle boundary has little effect on the I–V characteristics since near ideal Schottky I–V curves are obtained. The barrier height is calculated to be O.83 V which is higher than that of the single-crystal substrate. The ideality factor is 1.17 for a device containing a twin and low-angle boundaries. The high-angle grain boundary, however, significantly alters both the I–V and low-frequency C-V plots. The experimental data indicate that recombination centers and traps are introduced, resulting in an increase in recombination current and a reduction of the effective mobility. The conduction mechanisms for the two types of diodes are clearly distinguishable both in the dark and under illumination. In the photovoltaic operation under a tungsten lamp, we obtain an open-circuit voltage of O.48 V and a fill factor O.51. It appears that the chemical etching along with Schottky-barrier fabrication will provide a useful method to study the polycrystalline substrate for low-cost solar cell applications.