Environmental Engineering Reference
In-Depth Information
3.3 Pyrite Nanocrystal Photodetector Technology
While most focus has been on creating working PV devices with pyrite, other
devices can also benefit from its unique properties. Photodetectors could put to use
the high absorption coefficient and broad absorption spectra of pyrite. Wang et al.
reported the use of pyrite nanocrystals coupled with zinc oxide (ZnO) to create a
photodetector [ 64 ]. When MoO 3 is added as electron blocking, hole transport layer
between the pyrite nanocrystals and the gold electrode the dark current decreases
and the photocurrent increases. Without the MoO 3 layer large leakage current was
observed. Devices had a spectra response range from 450 nm to 1150 nm, which
can be attributed all to the pyrite since MoO 3 and ZnO do not absorb above
450 nm. This was the first example of making use of pyrite nanomaterial in a
photodetector device.
Our group has recently expanded the pyrite material system utilized in our PV
work to create a photodetector [ 65 ]. Pyrite cubes, Pyrite nanospheres, and CdS
material were used in the fabrication of such device, though deposition of the
material was vastly different. In the photodetector work a bulk heterojunction
structure was not wanted so a bi-layer structure was chosen. This was achieved by
a novel micro centrifugation deposition of the pyrite nanocrystals followed by a
chemical bath deposition of an over layer of CdS. It is shown that the final
photodetector device showed fast photoresponse time of 10 ms and high respon-
sivity of 174.9 A/W. Even more interestingly, these devices exhibited the ability to
tune the photocurrent in the presence of a magnetic field due to the creation of a
dilute magnetic semiconductor (DMS) phase that was created from the CBD
method of CdS growth. It is a challenge in the field to create a photodetector with
high sensitivity and quick temporal response that is visible, and every more
unheard of in the NIR region. In systems utilizing pyrite nanospheres, response
time was quicker than in systems using pyrite nanocubes. Pyrite nanocubes, not to
be outdone, showed response in the NIR due to their photoabsorption peak around
1200 nm. Figure 19 shows current-voltage characteristics of all devices made and
also EQE and absorption of thin films. Figure 20 shows the different on/off cycles
to show temporal response.
Since the CBD method is done in aqueous medium, a DSM interfacial layer of
CdFeS was found from the migration of Fe 3+ ions (due to oxidation of the pyrite in
water) into CdS layer. With this layer being present, it allows for the ability to turn
the intensity of the current by changing the magnetic field around the device.
Figure 21 shows the J-V curves of device testing when the magnet is moved a set
amount away from the sample. An overall change of 72.6 % current can be
achieved by simply changing the position of the magnet. This work shows the
versatility of the pyrite material system, not only as a photovoltaic material, but as
a potential system for photodetectors as well. Ongoing studies of creating better
photodetectors, especially for NIR response, are being conducted in our lab.
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