Research On Photovoltaic Performances For DSCs Of Carbon Counter Electrode Of Low-Temperature Fabrication

Dye-sensitized solar cells(DSCs) has some characteristics of low cost, simple manufacture and flexibility. Therefore, graphene nanosheets (GNs) with controllable layer structure are introduced in counter electrodes of DSCs, and several families of carbon-based electrodes are set up by low temperature synthesis (120℃) binding some carbon materials such as mesoporous carbon, and their photovoltaic performances are discussed and the causes of performance improvement are suggested, which provides foundamental for low-cost, flexible and high efficient DSCs. Studies show that:The conversion efficiency (η) increases linearly along with the content of active carbon in graphite/activated carbon counter electrode, while the fill factor (FF) parabolically increases. The improvement of η owes to the decrement of the charge-transfer impedance (RCT) and Nernst diffusion impedance (ZP). In addition, silver paste in graphite counter electrode can improve efficiency.With the process adjusting, the layer numbers of GNs can be regulated by oxidation reduction process. After introducing the counter electrode, with layer of GNs increasing, η increases at first and then decreases, when the number of layer is5, η reach to max. Via secondary heat treatment at300℃, the release of the active sites makes RCT and ZP of the GNs electrode reduced obviously, so that η increases from1.17%to2.07%, and the increase amplitude reaches to77%.The photovoltaic performances of the counter electrode composed of compound GNs blending with graphite, activated carbon, or mesoporous carbon respectively are different in virtue of layer and content of GNs. When the number of layers is5, the performance of the three families of counter electrode reaches to the best. And when the content is16.7%of GNs, the η of the three electrodes reaches to the best, and the graphite counter electrode performance is greately improved. The diffuse GNs in the counter electrode can play a "bridge effect", in other words, they can increase the photovoltaic properties by changing the series resistance (Rs). With the photoelectrode and the electrolyte being optimized, η of the counter electrode of GNs/graphite, GNs/activated carbon and GNs/mesoporous carbon assembled into DSCs is increased to2.46%,5.50%and8.22%respectively, and the increase amplitude reaches to63.6%,17.4%and37.4%respectively.