Cadmium sulfide nanowire arrays for window layer applications in solar cells

Arrays of 100 nm long n-cadmium sulfide (CdS) nanowires were investigated as replacement for the planar n-CdS film, which is presently used as a window layer in many solar cell devices. These arrays exhibited substantial transmission at wavelengths below 512 nm. Theoretical calculation involving the number of extra photons transmitted through the CdS nanowire window layer indicated a potential enhancement in photocurrent by 20.6% and in open circuit voltage by 10.2% over the device using planar CdS film as the window layer. Next, Au/CdS Schottky diodes were formed. Analysis of the current-voltage characteristics of these Schottky diodes showed smaller diode ideality factors and higher current density in devices with CdS nanowires than in devices with planar CdS film. Capacitance-voltage measurements yielded values of effective carrier concentration (N(x)) in the CdS nanowire. N(x) varied along the length of nanowire; it was higher near the top surface and lower, near the SnO2 base. In initial experiments, p-CdTe layer was deposited on top and a nanowire-CdS/CdTe photovoltaic device of 0.04 cm2 area exhibited short current density (Jsc) of 25.8 mA/cm2, open circuit voltage (Voc) of 722 mV and fill factor of 52.8%, resulting in an a power conversion efficiency value of 9.8%.