Improved photovoltaic cell performance based on Ge islands embedded into the intrinsic layer

We report on the significant improvements in photovoltaic cell utilizing Ge islands inserted in the intrinsic layer. It was found that an increase of short circuit current, J_SC, was partially contributed by the absorption of lower-energy photons while slight decrease of open circuit voltage owing to the presence of Ge was observed. This shows that a part of electron-hole pairs generated within the Ge dots was separated by the internal electric field and contributed to the increase of the spectral response. It was also observed that thicker intrinsic layer would exhibit a drastic decrease of J_SC. This reduction suggests that excessive recombination of photogenerated carriers take place in the stacked layers.