Spectrally selective optoelectronic films via photonic band engineering in absorbing media

In technologies requiring fine-tuned spectral responsivity such as finite bandwidth photon detection and multijunction solar cells, optoelectronic devices based on traditional semiconductors usually have to integrate external filters or empirically control the thicknesses of each absorbing layer. In this work, we propose an alternate solution that could realize spectral selectivity within the optoelectronic thin film itself: engineering photonic bands within the absorbing region of a semiconductor where the in-plane photonic modes couple strongly to the normal-incidence light at the γ point to tune the out-of-plane reflectivity and transmission spectra. Our optical simulations show that even in the presence of material absorption, we can use photonic crystal structures to tune the strong Fano resonance features in the out-of-plane transmission and reflection spectra induced by the in-plane photonic bands for spectral selectivity. Experimentally, we demonstrate a proof-of-principle photonic structure where a self-assembled polystyrene bead monolayer is infiltrated with PbS colloidal quantum dots for enhanced visible transparency, qualitatively matching predictions and showing promise for multijunction and transparent photovoltaics.