Growth and properties of amorphous Ge:H solar cells

We report on the growth and properties of a-Ge:H materials and solar cells. The materials and cells were grown using remote ECR plasma deposition with high (∼50:1) hydrogen dilution. Both p–i–n and n–i–n structures were made with this material on stainless steel substrates. The solar cells showed reasonable fill factors (59%). The measurement of subgap quantum efficiency revealed that the Urbach energy of valence band tails in devices was also very low, being ∼43 meV. Measurement of space charge limited current in n–i–n structures showed that the midgap defect density was in the mid-1016/cm3 eV range. Defect densities in the range of mid 1016/cm3 were also measured using drive level capacitance, and they were in agreement with SCLC results. Graded bandgap cells were made with this material. They showed an increase in voltage to 0.47 V when appropriate buffer layers were used. These results indicate that good quality a-Ge:H can be made for potential applications in solar cells and image sensors.