Solar Light-Induced Opacity of Mind Cells

Multi-interface solar cells exhibit a dramatically low UV- and blue-spectrum photovoltaic performance independently of the electronic quality of their surface. A paradox can even be observed, the better the electronic passivation the poorer the conversion efficiency. The effect can be explained by solar light-induced opacity, which reduces considerably or even totally the photon penetration, into the device bulk. This opacity results from a feedback occasioned by the free-carrier absorption: better surface passivation, higher free-carrier density, stronger surface dead zone absorptance. Particularly, the total energy of the incident short wavelength beam can be absorbed in front of a carrier collection limit buried in the emitter. This limit acts simultaneously on the electronic performance, blocking free-carriers, and on the optical performance, being at the origin of an enhancement of the absorptance. As a consequence, a thin surface stratum dominates the optical functions of MIND cells through the free-carrier gas confined inside it. The main characterization methods used were reflectivity and spectral response with a varying intensity incident beam. The investigation allows modification of the free-carrier confinement using different device architectures. The results demonstrate the domination of the free-carrier optical functions on the multi-interface cell conversion