High Photovoltaic Quantum Efficiency in Ultrathin van der Waals Heterostructures.

We report experimental measurements for ultrathin (<15 nm) van der Waals heterostructures exhibiting external quantum efficiencies exceeding 50% and show that these structures can achieve experimental absorbance >90%. By coupling electromagnetic simulations and experimental measurements, we show that pn WSe2/MoS2 heterojunctions with vertical carrier collection can have internal photocarrier collection efficiencies exceeding 70%.