This Small Business Innovation Research (SBIR) Phase I project describes an innovative concept to enhance the energy conversion efficiency of polycrystaline-Si solar cells by separating the absorption length from the minority carrier diffusion length. This new design is called lateral collection. The fabrication route employs scalable technologies such as imprint lithography and electrodeposition. The primary research objective is to demonstrate much higher current with polycrystalline silicon lateral collection solar cells compared to conventional solar cells of the same thickness. The broader/commercial impacts of this project will be the potential to significantly improve the energy conversion efficiency of polycrystalline Si solar cells. A major factor that lowers the energy conversion efficiency of polycrystalline silicon solar cell is that current carriers cannot be harvested from the relatively thick films that are needed to absorb sunlight. Specifically, the optimum polycrystalline silicon absorber thickness is >10 microns; however the current can only be extracted if it is generated within about 3 microns of the electrodes. The solution to this problem is to decouple the directions of light absorption and charge carrier collection. By incorporating microscale collecting structures into the active layer, this lateral collection design ensures that all charge carriers are generated within a short distance of a collecting surface. This technology may produce 60% more current than conventional devices, thus resulting in much higher energy conversion efficiency
