High Open Circuit Voltage in Atomically-Thin Photovoltaics

In order to achieve high power conversion efficiency approaching the Shockley-Queisser limit, a photovoltaic cell must maximize its photogenerated current and voltage output. In our previous works we demonstrated strategies for light trapping and record high photocurrent generation in transition metal dichalcogenide (TMDC) photovoltaic cells. Despite having bandgaps comparable to silicon and gallium arsenide (1.1 – 1.4 eV), TMDC-based photovoltaic devices reported to date exhibit considerably lower open-circuit voltages under 1-sun illumination, typically around 300 mV. In this work, we show that using a different device geometry with carrier-selective contacts, we can obtain record open-circuit voltages (700 mV) in vertical device heterostructures composed of nickel oxide/tungsten diselenide/titanium dioxide. In particular, we show via X-ray photoemission spectroscopy that nickel oxide and titanium dioxide can act as hole- and electron-selective contacts, respectively, enabling the unprecedented open-circuit voltages in TMDC-based photovoltaics. In addition, we perform optoelectronic device modelling to explain the device transport characteristics. In summary, our results show the potential for efficient photovoltaics using atomically-thin van der Waals materials.