Revisiting the Theory of Photocurrent in Solar Cells
Abstract
The built-in potential of p-n junctions plays a critical role in charge separation, which is fundamental to the photovoltaic effect. However, the conventional classical theory of photovoltaic effect in p-n junctions typically does not account for the quantitative influence of the built-in potential. In this study, we revisit the classical theory and propose an improved analytic expression of photocurrent by applying more accurate boundary conditions. Our improved expression reveals that the photocurrent comprises of two components: the conventional photocurrent and a previously unrecognized backward photocurrent. Latter reduces the total photocurrent, yet it has not been discussed in prior literature. The essential role of the built-in potential is to suppress this backward current. Furthermore, our improved expression of photocurrent predicts that the photocurrent vanishes under certain forward bias conditions. This prediction is experimentally validated using a commercial silicon solar cell, confirming the direct impact of the built-in potential on photocurrent behavior.