Graphene below the percolation threshold in TiO₂for dye-sensitized solar cells

Abstract

We demonstrate a fast and large area-scalable methodology for the fabrication of efficient dye sensitized solar cells (DSSCs) by simple addition of graphene micro-platelets to TiO2 nanoparticulate paste (graphene concentration in the range of 0 to 1.5 wt%). Two dimensional (2D) Raman spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM) confirm the presence of graphene after 500 C annealing for 30 minutes. Graphene addition increases the photocurrent density from 12.4 mA cm2 in bare TiO2 to 17.1 mA cm2 in an optimized photoanode (0.01 wt% graphene, much lower than those reported in previous studies), boosting the photoconversion efficiency (PCE) from 6.3 up to 8.8%. The investigation of the 2D graphene distribution showed that an optimized concentration is far below the percolation threshold, indicating that the increased PCE does not rely on the formation of an interconnected network, as inferred by prior investigations, but rather, on increased charge injection from TiO2 to the front electrode. These results give insights into the role of graphene in improving the functional properties of DSSCs and identifying a straightforward methodology for the synthesis of new photoanode

Metal Oxide Semiconductors for Dye- and Quantum-Dot-Sensitized Solar Cells

“…At high MWCNT loading, the conductivity of the electrodes decreases, which may result from CNT agglomeration. The same strategy was applied to integrate graphene platelets into 2D graphene bridges to increase electron collection and reduce charge recombination …”

Metal-free organic dyes for TiO2 and ZnO dye-sensitized solar cells

“…Other n -type metal oxide semiconductors, such for instance ZnO, SnO 2 , Nb 2 O 5 and In 2 O 3 can be used as alternative photoanode materials 28 29 30 31 32 33 34 35 36 , as well as composite systems, e.g. carbon nanotubes 37 38 or graphene 39 mixed with TiO 2 nanoparticles. Among all, ZnO is very promising, due to its electronic band structure (very similar to TiO 2 ) 30 and high electron mobility (one order higher than TiO 2 ) 40 41 42 .…”

Dye sensitized solar cell efficiency improvement using TiO2/nanodiamond nano composite

“…The addition of a large amounts of ND (1.5 wt% to 2.5 wt.%) result in very short electron lifetime, due to very fast electron transfer from the photo-anode to the electrolyte, resulting in very large electron recombination, which in turn negatively affects the cell performance. It can thus be conclude that the addition of moderate quantities of ND highly improves the PCE, but an excessive amount of ND induces an electrochemical short circuit, in which electrons are massively injected into the electrolyte and no longer collected at the anode [24].…”