Abstract:
Transitional metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS2) have
found application in photovoltaic cells as a charge transporting layer due to their high
carrier mobility, chemical stability, and flexibility. In this research, a photovoltaic device
was fabricated consisting of copper phthalocyanine (CuPc) as the active layer, exfoliated
and Au-doped MoS2, which are n-type and p-type as electron and hole transport layers,
respectively. XRD studies showed prominent peaks at (002) and other weak reflections
at (100), (103), (006), and (105) planes corresponding to those of bulky MoS2. The only
maintained reflection at (002) was weakened for the exfoliated MoS2 compared to the
bulk, which confirmed that the material was highly exfoliated. Additional peaks at (111)
and (200) planes were observed for the Au doped MoS2. The interlayer spacing (d002)
was calculated to be 0.62 nm for the trigonal prismatic MoS2 with the space group
P6m2. Raman spectroscopy showed that the E1
2
g (393 cm−1
) and A1g (409 cm−1
)
peaks for exfoliated MoS2 are closer to each other compared to their bulk counterparts
(378 and 408 cm−1
, respectively) hence confirming exfoliation. Raman spectroscopy
also confirmed doping of MoS2 by Au as the Au-S peak was observed at 320 cm−1
.
Exfoliation was further confirmed by SEM as when moving from bulky to exfoliated MoS2,
a single nanosheet was observed. Doping was further proven by EDS, which detected
Au in the sample suggesting the yield of a p-type Au-MoS2. The fabricated device
had the architecture: Glass/FTO/Au-MoS2/CuPc/MoS2/Au. A quadratic relationship
between I-V was observed suggesting little rectification from the device. Illuminated I-V
characterization verified that the device was sensitive and absorbed visible light. Upon
illumination, the device was able to absorb photons to create electron-hole pairs and
it was evident that semipermeable junctions were formed between Au-MoS2/CuPc and
CuPc/MoS2 as holes and electrons were extracted and separated at respective junctions
generating current from light. This study indicates that the exfoliated and Au-MoS2 could
be employed as an electron transporting layer (ETL) and hole transporting layer (HTL),
respectively in fabricating photovoltaic devices.
