Balance of photon management and charge collection from carbon-quantum-dot layers as self-powered broadband photodetectors.

ABSTRACT

Semiconductor colloidal quantum dots (QDs) have been regarded as promising fluorescent materials for chemical sensing, bio-detection and optical communications; yet it still remains challenging to bring out self-powered photodetectors based solely on QDs because the excited charges within QDs are extremely immobile due to their reduced dimensionalities and they hardly form effective photocurrents. Hence, we have attempted to decouple the light-absorption and charge-transport criteria in order to feature highly-sensitive, rapid-response and self-driven photodetectors based on single-layer carbon QD layers (CQDLs) via facile in situ self-assembling deposition with fine control over thickness. We show explicit dark-current suppression by visualizing charge blocking phenomena and screen effects due to layered CQDL structures, which alleviate the movement of leakage carriers crossing over the CQD interlayers. By examining the distribution of electric fields within CQDLs under light excitation, the spatial dependence of the light-trapping effect within CQDLs was confirmed. These features are strongly associated with the thickness tuning of CQDLs, while 65 nm of CQDL thickness could manifest remarkable photoresponsivity above 9.4 mA W-1 and detectivity above 5.9 × 1012 under broadband light illumination. These results demonstrate the insights gained from an understanding of broadband optoelectronics, which might potentially pave the way for further employment in functional photodetection.