Flexible graphene-/a-Si:H multispectral photodetectors

Abstract

Transparent conductive electrodes (TCEs) are ubiquitous and essential for photonic devices like solar cells, touchscreens and photodetectors. An increasing demand for TCEs may be met with graphene, which promises low production cost and an abundance of raw material and may enable flexible optoelectronic devices [1,2]. We report amorphous silicon (a-Si:H) multispectral photodetectors with a bias-tunable maximum spectral response on rigid and flexible substrates with graphene TCEs. Electrical and optical measurements compare reasonably well to conventional devices with transparent conductive oxide (TCO) TCEs (here: ZnO:Al, [3]), reaching over 50% of their responsivity. Graphene enables flexible multispectral photodiodes, in contrast to the brittle ZnO:Al. A further decisive advantage of the graphene TCEs is a broader spectral response into the UV region, which is otherwise limited by the absorption in the ZnO:Al. Artifacts due to refraction in the 220 nm thick ZnO:Al are suppressed in the atomically thin graphene TCEs. Bilayer graphene (BLG) electrodes improve the responsivity considerably.