10 research outputs found
Impact of Nanocrystal Spray Deposition on Inorganic Solar Cells
Solution-synthesized inorganic cadmium
telluride nanocrystals (∼4 nm; 1.45 eV band gap) are attractive
elements for the fabrication of thin-film-based low-cost photovoltaic
(PV) devices. Their encapsulating organic ligand shell enables them
to be easily dissolved in organic solvents, and the resulting solutions
can be spray-cast onto indium–tin oxide (ITO)-coated glass
under ambient conditions to produce photoactive thin films of CdTe.
Following annealing at 380 °C in the presence of CdCl<sub>2(s)</sub> and evaporation of metal electrode contacts (glass/ITO/CdTe/Ca/Al),
Schottky-junction PV devices were tested under simulated 1 sun conditions.
An improved PV performance was found to be directly tied to control
over the film morphology obtained by the adjustment of spray parameters
such as the solution concentration, delivery pressure, substrate distance,
and surface temperature. Higher spray pressures produced thinner layers
(<60 nm) with lower surface roughness (<200 nm), leading to
devices with improved open-circuit voltages (<i>V</i><sub>oc</sub>) due to decreased surface roughness and higher short-circuit
current (<i>J</i><sub>sc</sub>) as a result of enhanced
annealing conditions. After process optimization, spray-cast Schottky
devices rivaled those prepared by conventional spin-coating, showing <i>J</i><sub>sc</sub> = 14.6 ± 2.7 mA cm<sup>–2</sup>, <i>V</i><sub>oc</sub> = 428 ± 11 mV, FF = 42.8 ±
1.4%, and Eff. = 2.7 ± 0.5% under 1 sun illumination. This optimized
condition of CdTe spray deposition was then applied to heterojunction
devices (ITO/CdTe/ZnO/Al) to reach 3.0% efficiency after light soaking
under forward bias. The film thickness, surface morphology, and light
absorption were examined with scanning electron microscopy, optical
profilometry, and UV/vis spectroscopy
Inorganic Photovoltaic Devices Fabricated Using Nanocrystal Spray Deposition
Soluble
inorganic nanocrystals offer a potential route to the fabrication
of all-inorganic devices using solution deposition techniques. Spray
processing offers several advantages over the more common spin- and
dip-coating procedures, including reduced material loss during fabrication,
higher sample throughput, and deposition over a larger area. The primary
difference observed, however, is an overall increase in the film roughness.
In an attempt to quantify the impact of this morphology change on
the devices, we compare the overall performance of spray-deposited
versus spin-coated CdTe-based Schottky junction solar cells and model
their dark current–voltage characteristics. Spray deposition
of the active layer results in a power conversion efficiency of 2.3
± 0.3% with a fill factor of 45.7 ± 3.4%, <i>V</i><sub>oc</sub> of 0.39 ± 0.06 V, and <i>J</i><sub>sc</sub> of 13.3 ± 3.0 mA/cm<sup>2</sup> under one sun illumination