2 research outputs found
Efficient Modification of Metal Oxide Surfaces with Phosphonic Acids by Spray Coating
We report a rapid method of depositing
phosphonic acid molecular
groups onto conductive metal oxide surfaces. Solutions of pentafluorobenzyl
phosphonic acid (PFBPA) were deposited on indium tin oxide, indium
zinc oxide, nickel oxide, and zinc oxide by spray coating substrates
heated to temperatures between 25 and 150 °C using a 60 s exposure
time. Comparisons of coverage and changes in work function were made
to the more conventional dip-coating method utilizing a 1 h exposure
time. The data show that the work function shifts and surface coverage
by the phosphonic acid were similar to or greater than those obtained
by the dip-coating method. When the deposition temperature was increased,
the magnitude of the surface coverage and work function shift was
also found to increase. The rapid exposure of the spray coating was
found to result in less etching of zinc-containing oxides than the
dip-coating method. Bulk heterojunction solar cells made of polyhexylthiophene
(P3HT) and bis-indene-C<sub>60</sub> (ICBA) were tested with PFBPA
dip and spray-modified ITO substrates as well as polyÂ(3,4-ethylenedioxythiophene)/polyÂ(styrenesulfonate)
(PEDOT:PSS)-modified ITO. The spray-modified ITO solar cells showed
a similar open circuit voltage (V<sub>OC</sub>) and fill factor (FF)
and a less than 5% lower short circuit current density (<i>J</i><sub>SC</sub>) and power conversion efficiency (PCE) than the dip-
and PEDOT:PSS-modified ITO. These results demonstrate a potential
path to a scalable method to deposit phosphonic acid surface modifiers
on metal oxides while overcoming the limitations of other techniques
that require long exposure and post-processing times
Tandem Solar Cells from Solution-Processed CdTe and PbS Quantum Dots Using a ZnTe–ZnO Tunnel Junction
We developed a monolithic
CdTe–PbS tandem solar cell architecture in which both the CdTe
and PbS absorber layers are solution-processed from nanocrystal inks.
Due to their tunable nature, PbS quantum dots (QDs), with a controllable
band gap between 0.4 and ∼1.6 eV, are a promising candidate
for a bottom absorber layer in tandem photovoltaics. In the detailed
balance limit, the ideal configuration of a CdTe (<i>E</i><sub>g</sub> = 1.5 eV)–PbS tandem structure assumes infinite
thickness of the absorber layers and requires the PbS band gap to
be 0.75 eV to theoretically achieve a power conversion efficiency
(PCE) of 45%. However, modeling shows that by allowing the thickness
of the CdTe layer to vary, a tandem with efficiency over 40% is achievable
using bottom cell band gaps ranging from 0.68 and 1.16 eV. In a first
step toward developing this technology, we explore CdTe–PbS
tandem devices by developing a ZnTe–ZnO tunnel junction, which
appropriately combines the two subcells in series. We examine the
basic characteristics of the solar cells as a function of layer thickness
and bottom-cell band gap and demonstrate open-circuit voltages in
excess of 1.1 V with matched short circuit current density of 10 mA/cm<sup>2</sup> in prototype devices