Stanford Advisors

  • Eric Pop, Postdoctoral Faculty Sponsor

2019-20 Courses

All Publications

  • High-specific-power flexible transition metal dichalcogenide solar cells. Nature communications Nassiri Nazif, K., Daus, A., Hong, J., Lee, N., Vaziri, S., Kumar, A., Nitta, F., Chen, M. E., Kananian, S., Islam, R., Kim, K., Park, J., Poon, A. S., Brongersma, M. L., Pop, E., Saraswat, K. C. 2021; 12 (1): 7034


    Semiconducting transition metal dichalcogenides (TMDs) are promising for flexible high-specific-power photovoltaics due to their ultrahigh optical absorption coefficients, desirable band gaps and self-passivated surfaces. However, challenges such as Fermi-level pinning at the metal contact-TMD interface and the inapplicability of traditional doping schemes have prevented most TMD solar cells from exceeding 2% power conversion efficiency (PCE). In addition, fabrication on flexible substrates tends to contaminate or damage TMD interfaces, further reducing performance. Here, we address these fundamental issues by employing: (1) transparent graphene contacts to mitigate Fermi-level pinning, (2) MoOx capping for doping, passivation and anti-reflection, and (3) a clean, non-damaging direct transfer method to realize devices on lightweight flexible polyimide substrates. These lead to record PCE of 5.1% and record specific power of 4.4Wg-1 for flexible TMD (WSe2) solar cells, the latter on par with prevailing thin-film solar technologies cadmium telluride, copper indium gallium selenide, amorphous silicon and III-Vs. We further project that TMD solar cells could achieve specific power up to 46Wg-1, creating unprecedented opportunities in a broad range of industries from aerospace to wearable and implantable electronics.

    View details for DOI 10.1038/s41467-021-27195-7

    View details for PubMedID 34887383

  • High-Performance p-n Junction Transition Metal Dichalcogenide Photovoltaic Cells Enabled by MoOx Doping and Passivation. Nano letters Nassiri Nazif, K., Kumar, A., Hong, J., Lee, N., Islam, R., McClellan, C. J., Karni, O., van de Groep, J., Heinz, T. F., Pop, E., Brongersma, M. L., Saraswat, K. C. 2021


    Layered semiconducting transition metal dichalcogenides (TMDs) are promising materials for high-specific-power photovoltaics due to their excellent optoelectronic properties. However, in practice, contacts to TMDs have poor charge carrier selectivity, while imperfect surfaces cause recombination, leading to a low open-circuit voltage (VOC) and therefore limited power conversion efficiency (PCE) in TMD photovoltaics. Here, we simultaneously address these fundamental issues with a simple MoOx (x 3) surface charge-transfer doping and passivation method, applying it to multilayer tungsten disulfide (WS2) Schottky-junction solar cells with initially near-zero VOC. Doping and passivation turn these into lateral p-n junction photovoltaic cells with a record VOC of 681 mV under AM 1.5G illumination, the highest among all p-n junction TMD solar cells with a practical design. The enhanced VOC also leads to record PCE in ultrathin (<90 nm) WS2 photovoltaics. This easily scalable doping and passivation scheme is expected to enable further advances in TMD electronics and optoelectronics.

    View details for DOI 10.1021/acs.nanolett.1c00015

    View details for PubMedID 33852295