(495a) Enhanced Optoelectronic Functionality of Photovoltaic 2D Crystal-Nanoantenna Hybrids

Enhanced optoelectronic functionality of photovoltaic
2D crystal-nanoantenna hybrids

D. Keith Roper^a,b*_, Gregory T. Forcherio^c, Jeremy R. Dunklin^d,
Mourad Benamara^e, Luigi Bonacina^f, Yana Vaynzof^g,
Claudia Backes^h

^a
Microelectronics
and Photonics Graduate Program, University of Arkansas, Fayetteville, AR
72701        

^b Department of Chemical
Engineering, University of Arkansas, Fayetteville, AR 72701

^cArmy Research Laboratory, Adelphi, MD 20783

^dNational Renewable Energy
Laboratory, Golden, CO 80401

^eInstitute for Nanoscience and
Engineering, University of Arkansas, Fayetteville, AR 72701

^f GAP-Biophotonics, Université de Genève, Genève, CH
1211

^g Kirchhoff-Institute for Physics and Centre for
Advanced Materials, Ruprecht-Karls University Heidelberg, 69120 Heidelberg,
Germany

^h Chair
of Applied Physical Chemistry, Ruprecht-Karls University Heidelberg, 69120 Heidelberg,
Germany

     Two-dimensional
(2D) nanocrystals (NC) offer a direct bandgap spanning the solar spectrum as
well as enhanced electron mobility and gate tunability.  Decoration of 2DNC by
nanoantenna (NA) has enhanced measured photocurrent.  But challenges in simulating,
characterizing and fabricating 2DNC-NA hybrid structures has constrained their implementation
in functional photovoltaic devices.

    
This work examined optical modulation of photocurrent, carrier injection and
second harmonic generation (SHG) in 2DNC, i.e., graphene and transition metal
dichalcogenide (TMD), via optically active NA. Monolayer 2DNC used were
chemical vapor deposited (graphene) or liquid exfoliated from bulk (TMD).  2DNC
were decorated by gold (Au) and silver (Ag) NA through three methods (i)
evaporation, (ii) drop-casting and (iii) direct reduction (Fig 1; [2]). Electron
energy loss spectroscopy (EELS) was used to predict and induce plasmon bright,
dark, and hybrid modes. EELS enabled quantitative femtosecond-scale measurement
of spectroscopic plasmon dephasing and nanometer-resolved mapping of electric
fields on the 2DNC-NA hybrids (Fig 2). Coupled and discrete dipole simulations
were used to characterize radiative and intraband dephasing in order to
distinguish contributions to photocurrent from field enhanced electron hole
pair generation and carrier injection [3]. X-ray photoemission spectroscopy was
used to contrast physicochemical 2DNC-NA bonds vs. polyvinylpyrrolidone coatings
representing alternate pathways for carrier injection. A tunable laser scanning confocal microscope (LSCM)
was used to measure second harmonic generation of 2DNC-NA hybrids (Fig 3). A
computational scaffold supporting analysis spanning atom to nanometer scales
was used to develop compact structure-function relations in order to rationalize
measured values.      

    
Coordination of EELS, XPS, and LSCM offers
a comprehensive approach to characterize increased photocurrent from field enhanced electron hole pair
generation and from carrier injection in 2DNC-NA hybrids at high spatiotemporal
resolution.

 [1] G.T. Forcherio et al., in preparation. [2] J.R. Dunklin et al., in preparation. [3]
D.K. Roper et al., in preparation.