For lattice-mismatch, high-defect-density solar cells, the current-voltage curve is not perfects, and it always has high ideality factor and low shunt resistance. In traditional one-dimension circuit model of solar cells, there is a paralleled resistor R-p and recombination diodes with high ideality factor to simulate this imperfection. In this research, a delocalized recombination model is built based on the assumption that recombination could occur between trapped electrons from n type sides and trapped holes from p type side. The model with different parameters (i.e. defect volume w and recombination parameter C-p) is then added into current continuity equations and I-V curves of solar cells were calculated. With the increase of C-p, fill factor (FF) decreases obviously, followed by the decrease of short-circuit current and open-circuit voltage. Larger defect volume w would cause higher ideality factor. The effects of mobility on I-V curves were also calculated, low mobility leads to decrease of shunt resistance and fill factor. Two type of solar cells with different configurations were irradiated by 70 keV and the I-V curves show different degradation behaviors. Type A cell shows large decrease of shunt resistance indicating loss of mobility while type B cell shows increase of n(V) due to delocalized recombination. The difference is related to different thicknesses of GaInP.