Harry Atwater1 Giulia Tagliabue1

1, California Institute of Technology, Pasadena, California, United States

The strong absorption and visible spectrum energy bandgaps for the transition metal dichalcogenides (TMDCs) of molybdenum and tungsten render them as attractive candidates for photovoltaics (PV) and optoelectronics. Further, the atomically thin nature is favorable for efficient separation and collection of photo-excited charge carriers. Thus if the three major optoelectronic criteria, i.e., i) sunlight absorption, ii carrier collection and iii) operating voltage can be addressed for TMDC materials, they may be candidates for high efficiency photovoltaics and photocatalysis1. We recently demonstrated near-unity broad-band absorption of above band-gap photons for < 15 nm TMDC layers2, and have also achieved high external quantum efficiency in < 10 nm thick active layer photovoltaic devices in a pn junction of WSe2/MoS2 with graphene contacts3. To date, achievement of high open-circuit voltage (Voc) has remained an outstanding challenge for achieving high photovoltaic efficiency. We report here high open-circuit voltages (Voc) in TMDC absorbers based photovoltaic devices, achieved by tailoring the conduction and valence band-alignments between a single TMDC absorber layer and carrier-selective contact layers for electron collection (titanium oxide) and hole collection (nickel oxide), respectively. The band alignments measured using X-ray photoelectron spectroscopy indicate the asymmetric and selective nature of the metal oxide carrier-selective contacts, and we observe open circuit voltages exceeding 700 mV under AM 1.5 illumination at 1 Sun. We will also discuss TMDC passivation, and architectures for photocatalysts and photoelectrochemical devices that employ these materials as absorbers and catalysts.

1. Jariwala, D.; Wong, J.; Davoyan, A. R.; Atwater, H. A. ACS Photonics 2017, ASAP.
2. Jariwala, D.; Davoyan, A. R.; Tagliabue, G.; Sherrott, M. C.; Wong, J.; Atwater, H. A. Nano Lett. 2016, 16, (9), 5482-5487.
3. Wong, J.; Jariwala, D.; Tagliabue, G.; Tat, K.; Davoyan, A. R.; Sherrott, M. C.; Atwater, H. A. ACS Nano 2017, 11, 7230–7240.