Abstract
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 4.4 W g−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 46 W g−1, creating unprecedented opportunities in a broad range of industries from aerospace to wearable and implantable electronics.
Highlights
Semiconducting transition metal dichalcogenides (TMDs) are promising for flexible highspecific-power photovoltaics due to their ultrahigh optical absorption coefficients, desirable band gaps and self-passivated surfaces
The low optical absorption coefficient and brittle nature of Si lead to degraded performance in ultrathin, flexible Si solar cells and prevent their broader usage in applications demanding high power per weight and flexibility, for example in aerospace, transportation, architecture, and self-powered wearable and implantable electronics[2,3,4,5,6,7,8,9,10]
According to realistic detailed balance models[13], a power conversion efficiency (PCE) of ~27% can be achieved in ultrathin singlejunction TMD solar cells, leading to extremely high PS once implemented on lightweight flexible substrates[8]
Summary
Semiconducting transition metal dichalcogenides (TMDs) are promising for flexible highspecific-power photovoltaics due to their ultrahigh optical absorption coefficients, desirable band gaps and self-passivated surfaces. Fermi-level pinning, MoOx capping for doping, passivation and anti-reflection coating, and a clean, non-damaging direct transfer method to realize TMD solar cells for the first time on an ultrathin (5 μm), lightweight and flexible polyimide (PI) substrate.
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