AUTHOR=Manamela Lebogang , Fru Juvet N. , Kyesmen Pannan I. , Diale Mmantsae , Nombona Nolwazi 

TITLE=Electrically Enhanced Transition Metal Dichalcogenides as Charge Transport Layers in Metallophthalocyanine-Based Solar Cells

JOURNAL=Frontiers in Chemistry

VOLUME=8

YEAR=2020

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2020.612418

DOI=10.3389/fchem.2020.612418

ISSN=2296-2646

ABSTRACT=<p>Transitional metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS<sub>2</sub>) 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 MoS<sub>2</sub>, 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 MoS<sub>2</sub>. The only maintained reflection at (002) was weakened for the exfoliated MoS<sub>2</sub> 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 MoS<sub>2</sub>. The interlayer spacing (d<sub>002</sub>) was calculated to be 0.62 nm for the trigonal prismatic MoS<sub>2</sub> with the space group <italic>P</italic>6<italic>m</italic>2. Raman spectroscopy showed that the <inline-formula><mml:math id="M1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>E</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mn>1</mml:mn></mml:mrow></mml:msubsup></mml:math></inline-formula>g (393 cm<sup>−1</sup>) and A<sub>1g</sub> (409 cm<sup>−1</sup>) peaks for exfoliated MoS<sub>2</sub> are closer to each other compared to their bulk counterparts (378 and 408 cm<sup>−1</sup>, respectively) hence confirming exfoliation. Raman spectroscopy also confirmed doping of MoS<sub>2</sub> by Au as the Au-S peak was observed at 320 cm<sup>−1</sup>. Exfoliation was further confirmed by SEM as when moving from bulky to exfoliated MoS<sub>2</sub>, 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-MoS<sub>2</sub>. The fabricated device had the architecture: Glass/FTO/Au-MoS<sub>2</sub>/CuPc/MoS<sub>2</sub>/Au. A quadratic relationship between <italic>I-V</italic> was observed suggesting little rectification from the device. Illuminated <italic>I-V</italic> 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-MoS<sub>2</sub>/CuPc and CuPc/MoS<sub>2</sub> as holes and electrons were extracted and separated at respective junctions generating current from light. This study indicates that the exfoliated and Au-MoS<sub>2</sub> could be employed as an electron transporting layer (ETL) and hole transporting layer (HTL), respectively in fabricating photovoltaic devices.</p>