Abstract
Abstract The properties of pin solar cells based on photogeneration of charge carriers into low-mobility materials were calculated for two models. Ideal p- and n-type electrode layers were assumed in both cases. The first, elementary case involves only band mobilities and direct electron–hole recombination. An analytical approximation indicates that the power in thick cells rises as the 1 4 power of the lower band mobility, which reflects the buildup of space-charge under illumination. The approximation agrees well with computer simulation. The second model includes exponential bandtail trapping, which is commonly invoked to account for very low hole drift mobilities in amorphous silicon and other amorphous semiconductors. The two models have similar qualitative behavior. Predictions for the solar conversion efficiency of amorphous silicon-based cells that are limited by valence bandtail trapping are presented. The predictions account adequately for the efficiencies of present a-Si : H cells in their “as-prepared” state (without light-soaking), and indicate the improvement that may be expected if hole drift mobilities (and valence bandtail widths) can be improved.
Highlights
In this paper we discuss the device physics of solar cells based on low-mobility materials
Solar cells based on hydrogenated amorphous silicon (a-Si : H) [1,2,3], on polymers or organic materials [4], and dye-sensitized porous metal-oxide ‘‘membranes’’ [5,6] are examples of such cells
In this paper we shall analyze the device physics of low-mobility solar cells for two simple models, and apply this analysis to estimating the maximum achievable efficiency of solar cells based on hydrogenated amorphous silicon
Summary
In this paper we discuss the device physics of solar cells based on low-mobility materials. In this paper we shall analyze the device physics of low-mobility solar cells for two simple models, and apply this analysis to estimating the maximum achievable efficiency of solar cells based on hydrogenated amorphous silicon. We shall use computer simulations to illustrate solar cell function throughout this paper, for this simplest model we have found a simple, analytical approximation for the maximum power density P (in Watts/Area) in the limit of a low hole mobility mh:. We believe that these predictions are a fairly accurate guide to the best power densities that may be achieved in engineered solar cells based on a-Si:H, presuming that the difficult problems of achieving ideal electrode layers and suppressing defect formation have been solved
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