How Do We Control Material Processes at the Level of Electrons?
Progress on Grand Challenge
Efficient carrier transport in nanostructured films is
a prerequisite to exploiting unique nanoscale
physics in electronic devices. The Center for
Advanced Solar Photophysics has developed
effective approaches for fabricating high-mobility
nanocrystal films and used them to demonstrate
record-performance in solar cells, and prototype 3rd
generation devices harnessing “carrier
multiplication”.
Remaining Challenges
• Develop universal model of carrier transport in
nanostructured films, including the role of
mesoscopic order/disorder, informed by new
time- and spatially-resolved characterization tools
• Use model to assemble a “tool kit” for solutionfabrication of nanocrystal films with bulk-like
mobilities and micron-scale carrier diffusion
lengths.
New Horizons for Grand Challenge
The next step will require a recasting of the
concept of “at the level of electrons” to
encompass transport over device-relevant
distances. The key will be developing
methods to observe, characterize, and
manipulate electronic processes at the
mesoscale as the bridge between
atomic/nano and macro scales.
Refreshed Grand Challenge?
• Characterizing and modeling material
processes at the electron level still
fundamentally important
• The importance of mesoscale processes
can be stressed in a new, broadened
definition, or potentially in an additional
Grand Challenge.
Submitted by: Victor Klimov
Affiliation: Los Alamos National Laboratory
1
Carrier transport in quantum dot films: From fundamental
understanding to optimization in real devices
Scientific Achievement
(a)
Efficient carrier transport through assemblies of quantum
dots (QDs) is a prerequisite to harnessing their unique
physics in electronic devices. CASP scientists have made
numerous direction-setting contributions to the field of
conductive QD films in the context of photovoltaics (PVs).
First certified QD solar cells:
Luther, et al., Adv. Mater.
2010; Gao, et al., Nano Lett.
2011.
(b)
Mid-gap band in QD films:
Nagpal and Klimov, Nat.
Commun. 2011; Pal, et al.,
Adv. Funct. Mater. 2012.
Significance and Impact
(c)
Solar cell with EQE
> 100%: Semonin,
et al., Science 2012.
ALD infilling: Ihly, et
al., ACS Nano 2011;
Liu, et al., Nano Lett.
2011 and 2013.
(d)
By bringing together diverse expertise and capabilities,
CASP can systematically attack the problem of carrier
transport in QD films at multiple levels, from fundamental
optical studies, through rational design and assembly of
coupled QD films, all the way to fabrication of real PV
devices. As a result, CASP has both achieved important
firsts in QD solar cells, and contributed vitally to the
understanding of transport physics that will enable the
next performance breakthroughs.
Notable Accomplishments (at left)
a) First officially performance-certified “Quantum Dot Solar Cell”
b) Uncovering the role of mid-gap band in photoconductivity in PbS QD
(e)
films and detectors
c) First thin-film solar cell with >100% external quantum efficiency (EQE)
Transport in
through carrier multiplication
mesoscopically
ordered QD films: d) Record high carrier mobilities and stability in “all inorganic” QD films
M. Law, et al., in
through atomic-layer deposition (ALD) infilling
review.
e) Fabrication and studies of transport in QD films with mesoscale
ordering