OPAL 2: Rapid optical simulation of silicon solar cells

The freeware program OPAL 2 computes the optical losses associated with the front surface of a Si solar cell. It calculates the losses for any angle of incidence within seconds, where the short computation time is achieved by decoupling the ray tracing from the Fresnel equations. Amongst other morphologies, OPAL 2 can be used to assess the random-pyramid texture of c-Si solar cells, or the `isotexture' of mc-Si solar cells, and to determine (i) the optimal thickness of an antireflection coating with or without encapsulation, (ii) the impact of imperfect texturing, such as non-ideal texture angles, over-etched isotexture, and flat regions, and (iii) the subsequent 1D generation profile in the Si. This paper describes the approach and assumptions employed by OPAL 2 and presents examples that demonstrate the dependence of optical losses on texture quality and incident angle.