DEPENDENCE OF OPEN-CIRCUIT VOLTAGE OF AMORPHOUS-SILICON SOLAR-CELLS ON THICKNESS AND DOPING LEVEL OF THE P-LAYER

We have focused on the thickness and the boron-doping concentration of the p-layer of amorphous silicon solar cells and systematically obtai ned data for open circuit voltage (V(proportional-to)) and the built-i n potential to reveal the mechanism causing a high V(proportional-to). A highly doped p-layer gives a higher built-in potential in the entir e thickness range, but V(proportional-to) is limited by the carrier re combination caused by the doping-induced defects. A low-doped p-layer causes a higher V(proportional-to) in a sufficiently thick film becaus e less carrier recombination occurs due to the lower density of the do ping-induced defects. After light-soaking, significant V(proportional- to) degradation occurs with the low-doped p-layer. The light-induced d efects are not negligible compared with the initial defects in the low -doped p-layer and thus more carrier recombination occurs. Moreover, s ome of the acceptors are compensated by light-induced defects. The hig hly doped p-layer, however, does not cause much V(proportional-to) deg radation because the light-induced defects are negligible compared wit h the large number of doping-induced defects and acceptors. The experi mental data show that the midgap defects induced by doping or light-so aking near the p/i interface cause the V(proportional-to) limitation.