New approaches to improve the performance of thin-film radial junction solar cells built over silicon nanowire arrays

Owing to their enhanced light trapping and antireflection effects, silicon nanowires (SiNWs) provide an active research platform for a new generation of cost-effective and efficient solar cells. By optimizing the density of nanowires and depositing amorphous silicon (a-Si:H) on top of them, stable radial junction p-i-n devices with efficiencies in the range of 8-9% have already been realized, and there is still room for improvement. For instance, by modifying the SiNW/a-Si:H interface, an open-circuit voltage as high as 0.9 V has been achieved. In addition, increasing the bandgap of the window layer is found to be effective for blue-response enhancement. Modeling of equivalent structures with a-Si:H nanowires by rigorous-coupled wave analysis method shows that short-circuit current density can be improved up to 20 mA/cm², and changing the active material to crystalline silicon allows us to broaden the absorption to near infrared spectral region. Initial results with hydrogenated microcrystalline silicon as an active layer are also presented.