Mobility lifetime product - A tool for correlating a-Si:H film properties and solar cell performances

The missing correlation between film characteristics and a-Si:H-based p-i-n solar cells is still a controversial subject. The authors present a new parameter mu(0) tau(0), evaluated from steady-state transport measurements on a-Si:H layers, which can indeed relate film quality and cell performance as far as the latter is limited by the quality of the intrinsic [i] layer. Thereby, two specific features of the evaluated mu(0) tau(0) product can explain its successful role as a quality parameter for a-Si:H: First, the computation of mu(0) tau(0) takes into account the effects of the prevailing dangling bond occupation, which is very different in uniform films as compared to the occupation profile prevailing through the i layer of a p-i-n solar cell; second, the evaluated mu(0) tau(0) product combines information about band mobility and defect density; furthermore it avoids some of the well-known pitfalls of usual deep defect density measurements such as constant photocurrent method and photothermal deflection spectroscopy. Experimental data on a series of layers and p-i-n solar cells illustrates the determination of mu(0) tau(0) in a given practical case and its successful correlation with cell efficiency. In this context, an estimation for the ratio of charged to neutral capture cross sections sigma(+/-)/sigma(0) of around 50 is found. (C) 1996 American Institute of Physics.