CdS nanowire layers of enhanced transmittance for window layer applications in thin film solar cells

Arrays of n-CdS nanowires were investigated as replacement for the planar n-CdS film; the latter is presently used as a window layer in important photovoltaic devices like CdS-CdTe and CdS-CIGS. CdS nanowire arrays continued to exhibit substantial transmission even when the wavelength of incident radiation was well below 512 nm, which is the wavelength corresponding to the energy band gap of single crystal CdS. Theoretical calculation involving the number of excess photons transmitted through the CdS nanowire window layer indicated a potential enhancement in photocurrent by as much as 38% over the planar CdS film window layer device. Next, Au/CdS Schottky diodes were formed by depositing thin films of gold on the nanowire arrays. Analysis of the current-voltage characteristics of these Schottky diodes showed smaller diode ideality factors and higher carrier concentrations in devices with CdS nanowires than in devices with planar CdS films; these are desirable junction characteristics when the designer is trying to maximize the open circuit voltage and the power output.