Computer analysis of the role of <i>p</i>-layer quality, thickness, transport mechanisms, and contact barrier height in the performance of hydrogenated amorphous silicon <i>p</i>-<i>i</i>-<i>n</i> solar cells

Abstract

The transport simulations provided by the computer program AMPS have been used to give an in-depth analysis of the role of the p-layer contact barrier height, contact transport mechanism, p-layer thickness, and p-layer quality on the performance of hydrogenated amorphous silicon p-i-n solar cells. We demonstrate for the first time that, if the contact barrier height to the p-layer is below a critical value and if tunneling through the p-layer is not important, then the performance of cells with either active or dead p-layers varies with contact barrier height regardless of p-layer thickness. We show that, even for an optimistic p-layer active doping density of 1019 cm−3, this critical barrier height is high (∼1.2 eV). Our analysis implies that one of two situations must occur in an actual a-Si:H p-i-n structure: the p-layer contact plays an important role in determining cell efficiency, or the tunneling of holes through the front contact/p-layer interface must be important. Comparison of simulated results, with and without tunneling, with experimental data suggests that tunneling is occurring in actual devices and is important in efficient structures.