Introduction to Light Trapping in Solar Cell and Photo-detector Devices

Appendix A

Yablonovitch Limit Derivation

A.1. Introductory comments

We noted in Section 1.3.2.1 that ideal diffuse reflection at textured surfaces of an absorber material can trap light and thereby enhance absorption. An analysis by Yablonovitch using geometrical (ray) optics showed this enhancement can be as much as 4n² where n is the absorber’s index of refraction [11]. Since geometrical optics is used, it is inherently assumed that the thickness of the absorber t is greater than the wavelength λ of the radiation, which may not be true in some light-trapping structures. In this appendix, we derive this 4n² factor following the approach of Ref. [11]. In so doing, we will take the opportunity to explore the interpretations, implications, and ...