A freeware program for precise optical analysis of the front surface of a solar cell

Abstract

This paper describes a freeware program that computes the optical losses associated with the front surface of a silicon solar cell. The optical losses are not trivial to assess because (i) the refractive index and extinction coefficient of silicon, antireflection coatings (ARCs), and encapsulants varies with wavelength; (ii) cells are usually textured such that the light reflects multiple times from the front surface; (iii) light can be polarised, particularly after the first ‘bounce’ from a textured surface; and (iv) the incident spectrum and the cell's quantum efficiency varies with wavelength. The freeware program takes all of these aspects into account to calculate reflection from the solar cell, absorption in the ARCs, transmission into the silicon, and the equivalent current that is generated for any given spectrum. When modelling textured silicon, the program is restricted to normally incident light and pyramidal morphologies. The program computes solutions within one second for regular upright pyramids, regular inverted pyramids, and random upright pyramids—making it much faster than ray tracing. We provide an example of how the freeware can be employed to determine the optimal thickness of an ARC with and without encapsulation. The example demonstrates that the optimal thickness cannot be determined from reflection measurements when absorption in the ARCs is significant. The program is readily adaptable to assess ARCs on glass and thin-film solar cells.