Optimization of multijunction a-Si:H solar cells using an integrated optical/electrical model

An phenomenological model for multijunction amorphous silicon solar cells which integrates a detailed optical model and an equivalent circuit model with a voltage-dependent photocurrent was developed. The model equations accurately describe the light J-V curves for a-Si:H and a-SiGe:H single junction cells using carrier transport properties comparable to values reported in the literature and which agree closely with values derived from quantum efficiency measurements. Closed form expressions for collection efficiency are derived by approximating the carrier generation profile by an exponential distribution. This new model can be used to predict cell behavior with changes in i-layer thickness and bandgap, carrier mobility-lifetime, and illumination. The model has been combined with a powerful multivariable optimization routine to analyze alternative cell designs. The model is described and representative results are presented.