Solution-processed semiconducting materials are promising
for realizing
high-performance, low-cost, and flexible energy conversion devices.
In particular, hybrid structures comprising colloidal quantum dots
(CQDs) and organic molecules have been proposed to achieve broadband
absorption across the visible-to-infrared solar spectrum. However,
the photophysical mismatch present at CQD/organic interfaces limits
charge extraction, resulting in low power conversion efficiency (PCE).
In this study, we sought to overcome this photophysical mismatch,
addressing the CQD/organic interface using a library of surface ligands
with different functions. We established, using both experiments and
theoretical calculations, that thiol termination of the CQD surface
reduced the interfacial barrier, resulting in a 4-fold higher charge
transfer efficiency at the maximum power point bias. The CQD/mixed-organic
heterojunction solar cells exhibit a record photocurrent density of
33.3 mA/cm2 and near-unity broadband quantum efficiency
up to 1100 nm, demonstrating the potential of these devices to harvest
infrared solar photons in all-solution-processed tandem devices.
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