Abstract
Carbon-based nanomaterials have successively remained at the forefront of different research fields and applications for years. Understanding of low-dimension carbon material family (CNT, fullerenes, graphene, and graphene quantum dots) has arrived at a certain extension. In this report, graphene quantum dots were synthesized from graphene oxide with a microwave-assisted hydrothermal method. Compared with conventional time-consuming hydrothermal routes, this novel method requires a much shorter time, around ten minutes. Successful formation of quantum dots derived from graphene sheets was verified with microscopic and spectroscopic characterization. Nanoparticles present a diameter of about 2-8 nm, blue emission under ultraviolet excitation, and good dispersion in polar solvents and can be collected in powder form. The synthesized graphene quantum dots were utilized as a hole transport layer in organic solar cells to enhance the cell quantum efficiency. Such quantum dots possess energy levels (Ec and Ev) relevant to HOMO and LUMO levels of conductive polymers. Mixing P3HT:PCBM polymer and graphene quantum dots of sufficient extent notably helps reduce potential difference at interfaces of the two materials. Overall efficiency consequently advances to 1.43%, an increase of more than 44% compared with pristine cells (0.99%).
Highlights
Organic solar cells (OSC), a highly promising branch in the grand photovoltaic tree, draw considerable involvement from either research or development sectors
The most prevalent heterojunction structure based on P3HT:PCBM host material has been regularly reported with promising achievements [5,6,7]
We report the successful synthesis of Graphene quantum dot (GQD) from graphene oxide via a one-step top-down method by using reducing agent NH3 and thermal energy from microwave oven to oxidize raw graphene oxide
Summary
Organic solar cells (OSC), a highly promising branch in the grand photovoltaic tree, draw considerable involvement from either research or development sectors They hold various important advantages like environment-friendliness, low cost, large-area production and simple fabrication techniques (screen-printing, spin-coating, and spray pyrolysis) [1,2,3,4]. One commonly accepted method is to integrate organic solar cells with inorganic nanostructured materials (CdSe, CdS, and PbSe) to constitute hole/electron transport, hole/electron extract, or hole/electron blocking layers [11] Such layers play a significant role in creating intermediate energy levels, well-fitting for Ec, Ev levels of active layers in optoelectronic devices, to reduce potential barrier difference between active layers and electrodes or between active layers themselves. This can be recognized as an ideal value; solar cells with GQDs are still of high potential and their efficiencies are predicted to overcome the theoretical number of 30% [20]
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