Doped Graphene And Their Application In Dye Sensitized Solar Cells

Dye-sensitized solar cells(DSSCs)have been universally regarded as one of the most promising third generation solar cells since the seminal work reported in 1991,due to their ease of fabrication,low cost,high flexibility and environmental friendliness.By virtue of the excellent conductivity and outstanding electrochemical activity,Platinum(Pt)are widely employed as the benchmark counter electrode(CE)material in DSSCs.However,Pt,one of the most expensive rare metals,enormously raises the cost of DSSCs,thereby impeding their commercial production.Therefore,it is of great significance to exploring efficient,cheap and abundant CE materials for DSSCs.Pt-free alternative materials previously proposed as CEs in DSSCs include carbon materials,transition metal compounds,conductive polymers,hybrids and so forth.Among them,carbon materials have shown great potential for practical use in terms of low cost,earth-abundance,excellent conductivity and high resistance against electrolyte corrosion.Particularly,graphene,discovered in 2004,has become a star material due to its unique structure and extraordinary properties,thus causing an explosion of research interest in DSSCs.In this thesis,a range of doped graphene materials were prepared via chemical vapor deposition(CVD),and were applied as CEs for DSSCs.The main contents are as follows:1.Nitrogen(N)-doped,sulfur(S)-doped and nitrogen/sulfur dual-doped transparent graphene-like carbon films(GFs)were synthesized by chemical vapor deposition(CVD),and were employed as CEs for bifacial DSSCs.The doped GFs showed dramatically enhanced electrochemical activities compared to pristine graphene.Benefit from the positive synergetic effects of N and S atoms,N/S dual-doped graphene exhibited the best electrochemical activity.Bifacial DSSCs with high transparent N/S dual-doped GFs as CEs achieved power conversion efficiencies(PCE)of 4.22%and 3.45%under front-side illumination and rear-side illumination,respectively.2.Phosphorus doped porous graphene with huge specific surface area(1627.8 m2·g-1)was prepared via chemical vapour deposition method using porous MgPO4 as the P source and template,and was applied as the CE for DSSC.Due to its abundant catalytic sites originated from high surface area,along with the P heteroatom doping strategy which further enhanced its intrinsic catalytic activity,DSSCs with phosphorus doped porous graphene as CEs exhibited a high power conversion efficiency of 7.08%,which achieve 98.5%that of DSSCs with Pt as CEs(7.19%).These results indicate that heteroatom doping,particular dual-doping,is an effective strategy for improving the electrochemical activity of graphene material.Limited by the surface area of CVD-grown carbon films that cannot render them with sufficient active sites,carbon films based DSSCs yield a relatively low PCEs.However,with their high transparence,carbon films can be applied in bifacial dye sensitized solar cells which possess the capacity to utilize incidental light from both front-and rear-sides.Combining the high surface area that provide CE materials with abundant active sites and heteroatom doping which further enhance their intrinsic electrochemical activities,phosphorus doped porous graphene based DSSCs shows excellent electrochemical activity,thereby exhibiting comparable photovoltaic performance compared to that of Pt.