(Invited) Photon Management Using Si Nanocrystals and Er3+ Ions: Generation of Hot Carries upon Absorption of Low-Energy Photons

Abstract

The most important limitation for efficiency of photovoltaic energy conversion appears due to the striking mismatch between the broad-band character of the solar radiation and the discrete operation mode of solar devices. Large losses appear at both edges of the solar spectrum. In particular the low-energy photons are commonly not absorbed and escape conversion. Here we discuss how this can be resolved by spectral conversion, making use of active layers of Si nanocrystals in an SiO2 matrix. As a possible solution, we consider generation of hot carriers upon sequential intraband absorption of two or more low-energy photons and present experimental data in support of this. Configurations are proposed in which the efficient spectral conversion could be achieved and their feasibilities are discussed. We also discuss the fast emission from Er3+ ions, purposefully introduced into the active layer, which can be used to trace successful generation of hot carriers, and in that way serve to evaluate specific excitation schemes.