High-performance porphyrin sensitized solar cell with graphene as an efficient hole transporting layer

TiO2-based dye-sensitized solar cells (DSSCs) offer one of the most promising alternatives to sustainable, clean, and renewable energy for transferring inexhaustible sunlight into electricity, as they possess advantages such as low cost and environmental friendliness, and they can, in principle, be produced on a large scale [1]. As the key component of DSSC, photoanode film plays an important role in adsorbing dyes and transferring the photogenerated electrons to external circuit. An ideal photoanode material should balance the two beneficial factors to maximize the photovoltaic performance [2]. Also Graphene had been considered as a promising material for producing transparent conducting films having high flexibility, remarkably high electrical mobility and opticaltransparency, and carbon being an inexpensive source material. TiO2/Graphene (TiO2/Gr) is expected to have ultrahigh specific surface area and excellentconductivity, which approve higher photovoltaic performance of DSSCs. In this work, however, TiO2/graphene-based DSSCs were fabricated without thepreproduction treatment. The effects of graphene on the photocurrent, voltage, and power conversion efficiency of the DSSCs were evaluated. It was determined that, for a TiO2-based DSSC without graphene, short-circuit current density (Jsc), open-circuit voltage (Voc), fill factor (FF), and power conversion efficiency (η) were 0.27 μA/cm2, 0.36 V, 0.652, and 6.34% respectively. Furthermore, the best performance of TiO2/graphene-based DSSCs exhibited a Jsc of 0.32 μA/ cm2, Voc of 0.37 V, FF of 0.59, and η of 6.96%. In addition, current densities at all voltages are higher for this best TiO2/graphene-based DSSC than forTiO2-based DSSC. These results indicate that the incorporation of grapheme can increase Jsc and η by 18.5 and 9.7%, respectively. It was reported that the power conversion efficiency (η) of TiO2 graphene-based DSSCs, which were fabricated with a prereduction step, was 9.7% higher than that of a TiO2- based DSSC without graphene. We work, also shows that the enhancements of Jsc and η are dependent on the content of Gr. As the graphene content increased, Jsc increased from 0.27 to 0.32 μA/cm2 and then decreased. The concentration of original graphene oxide in the TiO2/graphene composite, which is associated with the maximum Jsc (0.32 μA/cm2), is 0.8 wt %. The power conversion efficiency (η) of DSSCs exhibited a change similar to that of Jsc with increasingthe content of graphene.