Closed-form model for the open circuit voltage of solar cells with shunt resistance, bias-dependent photocurrent and double exponential terms

The parasitic shunt resistance, bias dependence of the photocurrent and phenomena causing a second exponential term in the current density (J)-voltage (V) equation reduce the open circuit voltage, Voc, of illuminated solar cells below the ideal value predicted by the J-V equation having only a single exponential term. This study reports an approximate closed-from solution of the transcendental Voc equation which directly reflects these losses. The solution estimates Voc as a weighted parallel combination of the limiting Voc values corresponding to the domination of one of the several terms of the Voc equation. The solution allows quick design calculation of the Voc of a wide variety of cells in terms of all physical parameters, and provides insight into the influence of losses owing to various factors. © 2012 The Institution of Engineering and Technology.