DETERMINATION OF THE QUALITY OF a-Si:H FILMS: “TRUE” TRANSPORT PARAMETERS

For the characterisation of a-Si:H layers, steady-state photoconductivity (SSPC) and steady-state photocarrier grating (SSPG) are currently used. But the p?-products deduced from these measurements are a function of the prevailing dangling bond occupation in the film and, thus, are not a measure of material quality. In the present paper the authors introduce the product PO+‘, which is independent of dangling bond charge and which monitors material quality in terms of band mobility p” and capture time TO,the latter being, in its turn, inversely proportional to dangling bond density. They present a simple evaluation procedure to deduce pore from simultaneously performed SSPC and SSPG measurements. In undoped, but slightly n-type a-Si:H, the quality of the material will typically be related to the ambipolar diffusion length rather than to photoconductivity. The application of this method to a series of undoped a-Si:H films and solar cells incorporating these materials exhibited a good correlation between film properties and cell performances.