The limiting efficiency of the compositionally graded bandgap solar cell is calculated using a 1-D numerical simulator. Our simulator calculates the limiting efficiency by solving the coupled semiconductor equations, namely, Poisson's equation, the current continuity equations, together with the Boltzmann photon equation, rather than the detailed balance equations that are usually used in such calculations. The non-avoidable radiative and Auger bulk losses are the only losses considered in the calculations. The effect of photon recycling on the cell's parameters is included in the calculations of radiative recombination rates. We verified numerically that bandgap grading, under optimum profile, increases the limiting efficiency of the solar cell, over the previously published values. The effect of the bandgap grading on desensitizing the surface of the cell is discussed. (c) 2006 Elsevier Ltd. All rights reserved.