A computer simulation model of amorphous silicon solar cells using a Scharfetter and Gummel solution of Poisson’s equation and Taylor and Simmons occupancy statistics for the dangling bond gap states (Dstates), has been developed. With a suitable choice of parameters, the numerical results for solar cell collection efficiency and dark and illuminatedI‐Vcharacteristics agree well with experimental values. The model has been used specifically to study the influence of interface states at the TCO‐p(transparent conductive oxide),p‐i,i‐n, andn‐metal interfaces and to explain the beneficial role of a graded‐band‐gap layer at thep‐iinterface.