Polyelectrolyte multilayer-assisted fabrication of p-Cu2S/n-CdS heterostructured thin-film phototransistors

Abstract

We demonstrate meticulous fabrication of p-Cu₂S/n-CdS heterojunction thin films using a facile wet-chemical approach. Ion exchange of Cu⁺ with Cd²⁺ is a serious problem during preparation of Cu₂S/CdS multilayered thin films. This issue was addressed by employing polyelectrolyte multilayers on the CdS surface, which completely prevented CdS corrosion, thereby allowing fabrication of heterostructured Cu₂S/CdS films. The formation of polyelectrolyte multilayers is monitored using cyclic voltammetry. The heterostructured films are characterized by structure and morphology. We further employed these films as modified p-channel, p-Cu₂S/n-CdS thin-film phototransistors, where n-CdS acts as the electron transporting and hole-blocking layer that extracts and grounds the photogenerated electrons. This device exhibited a significant increase in photocurrent density (>75 times), drift mobility (>87 times), and good linearity without having to apply gate voltage, when compared to its individual component device.