Abstract:
The most frequently used counter electrode (CE) in dye‐sensitized solar cells
(DSSCs) is platinum on fluorine‐doped tin oxide glass. This electrode has excellent electrical conductivity, chemical stability, and high electrocatalytic affinity
for the reduction of triiodide. However, the high cost of metallic platinum and
the poor electrochemical stability pose a major drawback in the commercial
production. This has necessitated a search for a non‐precious metal and
metal‐free electrocatalyst that demonstrates better catalytic activity and longer
electrochemical stability for practical use in DSSCs. Graphene has been at the
centre of attention due to its excellent optoelectronic properties. However, a
defect‐free graphene sheet is not suitable as a CE in DSSCs, because of its neutral polarity which often restricts efficient charge transfer at the
graphene/liquid interface, irrespective of the high in‐plane charge mobility.
Hence, heteroatom‐doped graphene‐based CEs are being developed with the
aim to balance electrical conductivity for efficient charge transfer and charge
polarization for enhanced reduction activity of redox couples simultaneously.
The elements commonly used in chemical doping of graphene are nitrogen,
oxygen, boron, sulfur, and phosphorus. Halogens have also recently shown
great promise. It has been demonstrated that edge‐selective heteroatom‐
doping of graphene imparts both efficient in‐plane charge transfers and polarity, thereby enhancing electrocatalytic activity. Thus, heteroatom‐doped
graphene serves as a good material to replace conventional electrodes and
enhance power conversion efficiency in DSSCs. The focus is to reduce the cost
of DSSCs. This review explores the performance of DSSCs, factors that influence the power conversion efficiency, and various physicochemical properties
of graphene. It further outlines current progress on the synthetic approaches
for chemical doping (substitutional and surface transfer doping) of graphene
and graphene oxide with different heteroatoms in order to fine‐tune the electronic properties. The use of heteroatom‐doped graphene as a CE in DSSCs
and how it improves the photovoltaic performance of cells is discussed.
