H-2-dilution vs buffer layers for increased V-oc

Hydrogen dilution and buffer layers, as two ways to obtain higher V-oc values in a-Si:H p-i-n solar cells, are directly compared in the present study. Special emphasis is laid on stability against light soaking. H-2-dilution in combination with lower substrate temperature yields higher Voc values and better stability as compared to buffer layers. However, light absorption is decreased due to the increased gap in H-2-diluted cells. The stability of buffer layer cells can remarkably be ameliorated by boron doping and H-2-dilution of the a-SiC:H buffer layer. However, stabilized efficiency is higher for optimized diluted cells than for cells with a buffer layer. An a-Si/a-Si stacked cell with a graded dilution for both cells yielded 10% initial efficiency with 17% relative degradation. Diluted a-Si:H cells at lower temperature become specially interesting in combination with a microcrystalline bottom cell. For such a ''micromorph'' tandem cell we obtained 11.4% initial efficiency.