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

Graphene-on-semiconductor heterojunction solar cell is an emerging class of photovoltaics with potential for efficient and reliable energy conversion systems. The interfaces between graphene and lightly-doped semiconductor play a key role in charge-carrier separation and recombination dynamics. Owing to the low Schottky barrier height-induced interfacial charge carrier recombination, the 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 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 graphene/h-BN/Si PV cell is examined. Thin films of h-BN are directly synthesized on 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 metal-insulator-semiconductor (MIS)-type junction, where the h-BN acts as an electron-blocking layer to avoid interfacial charge carrier recombination. A 4-fold increase in open-circuit voltage (VOC) is found for 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 Schottky barrier height 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 an evolution of new 2D/2D/3D nanoarchitectures for mechanically-robust, high performance, and durable optoelectronic functionalities.