Colloidal Quantum-Dot Photodetectors Exploiting Multiexciton Generation

Abstract

Multiexciton generation (MEG) has been indirectly observed in colloidal quantum dots, both in solution and the solid state, but has not yet been shown to enhance photocurrent in an optoelectronic device. Here, we report a class of solution-processed photoconductive detectors, sensitive in the ultraviolet, visible, and the infrared, in which the internal gain is dramatically enhanced for photon energies Ephoton greater than 2.7 times the quantum-confined bandgap Ebandgap. Three thin-film devices with different quantum-confined bandgaps (set by the size of their constituent lead sulfide nanoparticles) show enhancement determined by the bandgap-normalized photon energy, Ephoton/Ebandgap, which is a clear signature of MEG. The findings point to a valuable role for MEG in enhancing the photocurrent in a solid-state optoelectronic device. We compare the conditions on carrier excitation, recombination, and transport for photoconductive versus photovoltaic devices to benefit from MEG.

Solution-processed hybrid perovskite photodetectors with high detectivity

“…The 3-dB bandwidth decreased from 2.9 to 0.8 MHz when the device area increased from 0.01 to 0.1 cm 2 , because the speed is related to the RC constant of the circuit. It is noted that the response speeds of our perovskite photodetectors presented here are faster than most of the organic, quantum dot and hybrid photodetectors (typically on the order of millisecond) [4][5][6][7][8][9][10] and slightly slower than the silicon diode in Fig. 5a (r20 ns).…”

“…And a built-in or applied electric field is necessary to separate the electrons and holes to produce an electric current. Various types of semiconductor materials have been applied in photodetectors, such as Si, InGaAs, ZnO, GaN, carbon nanotubes, quantum dots and conjugated polymers [1][2][3][4][5][6][7][8][9][10] . Although certain applications require different features, the key figure-of-merit parameters are responsivity (R), detectivity (D*), noise equivalent power (NEP), linear dynamic range (LDR) and response speed.…”

Solution-processed semiconductors for next-generation photodetectors

“…The potential of this process has been explored in several material systems and architectures. [48][49][50][51][52] The successful implementation of CQD solids into full photodiode architectures remained elusive until 2007, partly due to a limited understanding and control over energy levels, surface chemistry and density of defect states. 53 Record sensitivity-bandwidth combinations, with a D*exceeding 10 12 Jones in the short-wave IR and a 3dB bandwidth up to 5 MHz, were achieved in Schottky PbS CQDs photodiodes; this was accomplished by a combination of improved carrier mobility via a more complete ligand exchange and a carrier extraction strategy that ensured drift collection dominated over diffusion.…”

Observation of Biexcitons in Nanocrystal Solids in the Presence of Photocharging

“…In addition to photovoltaic and lasing applications, the MEG concept has also been shown to significantly improve photodetector device performances. 25 For all of these application areas, the most pronounced limiting effect is the nonradiative Auger recombination (AR) of MEs. Therefore, the suppression of AR is also the subject of intense research in order to benefit from the MEs most effectively.…”