Temperature dependent device characteristics of graphene/h-BN/Si heterojunction

Abstract

Graphene-on-semiconductor heterojunction solar cell is an emerging class of photovoltaics (PV) with potential for efficient and reliable energy conversion systems. The interface between graphene and a lightly doped semiconductor plays a key role in charge-carrier separation and recombination dynamics. Owing to the low Schottky barrier height (ϕSBH)-induced interfacial charge carrier recombination, graphene-on-silicon (Si) heterojunction solar cells suffer from instability in power conversion efficiency over time. Therefore, it is critical to engineer the interface to enhance the barrier height by interfacing a chemically stable, insulating, and atomically thin layer. Further, the temperature dependent photovoltaic characteristics of such stacked architectures are unknown, and temperature dependent behavior is critical to understand the metal-insulator-semiconductor (MIS) junction behavior and photovoltaic phenomenon. Here, we have introduced hexagonal boron nitride (h-BN) as a tunneling interlayer in graphene-on-Si heterojunction solar cells, which enables the passivation of the chemical dangling bonds on the Si surface. The effect of temperature on the performance of a graphene/h-BN/Si PV cell is examined. Thin films of h-BN are directly synthesized on a lightly doped Si surface via a bottom-up chemical-surface-adsorption strategy followed by the transfer of a graphene monolayer. The 2D layer-on-2D layer-on-3D bulk semiconductor nanoarchitecture of graphene/h-BN/Si forms a MIS-type junction, where the h-BN acts as an electron-blocking layer to avoid interfacial charge carrier recombination. A four-fold increase in open-circuit voltage (Voc) is found for the graphene/h-BN/Si heterojunction cell (0.52 V) in contrast to the graphene/Si cell (0.13 V), which is due to the increase in the ϕSBH and hence built-in electric potential. Interestingly, the Voc linearly decreases by only ~4% with every 10 K increase in temperature. This work will lead to the evolution of new 2D/2D/3D nanoarchitectures for mechanically robust, high performance, and durable optoelectronic functionalities.