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The efficiency of dye-sensitized solar cells (DSSC) has been limited by the inherent slow transport of charges in the TiO2 photoanode. The trap-limited diffusion of charges in the semiconductor prevented photoanodes from having thickness greater than 15 µm, thus limiting the potential of DSSC. This is especially with more recent research moving away from iodine-based electrolyte that requires a thicker photoanode. Thicker photoanodes means higher potential efficiency due to better light harvesting without resorting to scattering or reflecting layers to trap light as with thin photoanodes. Graphene had been added to TiO2 photoanodes in other research but in the form of rGO and suffered from increasing electron recombination at higher concentration. In this study, shear-exfoliated graphene was successfully incorporated into TiO2 nanofibers via electrospinning to produce fiber with diameter 52–73 nm in the photoanode with graphene in roll-up form inside the nanofibers eliminating edge effect of 2D graphene sheet that causes electron recombination. The nanofiber-based photoanode showed significantly longer electron diffusion length with little impact on recombination, primary due to higher electron diffusion coefficient. As a result, a thicker optimal photoanode, 23 µm, can be obtained with device efficiency measured at 8.9%, which is 22% higher than that without graphene with optimal thickness of 13 µm. The graphene also showed no interference in dye loading density of N719 dye. For the first time, we have demonstated that the electrospun TiO2/graphene nanofibers is a potential starting point to thicker, more efficient DSSCs.

Solution-processable organic–inorganic hybrid perovskites have been successfully used as light-harvesting materials in efficient photovoltaic cells. Here, an efficient and simple approach is reported for using dimethylsulphoxide (DMSO) to increase crystal size and hydrochloric acid (HCl) to further retard crystallization thereby improving uniformity and crystallinity of the perovskite film. With this synergistic approach, large uniform perovskite crystals over one micron in size with superior quality perovskite film without pinholes resulted as confirmed by both XRD and SEM images. The fabricated planar heterojunction solar cell has reached efficiency of 17.8%. Both the best and average solar cells fabricated with this approach using DMSO reveal that a 10%-11% increase in efficiency as a result of conditioning with HCl which controls crystallization preventing undesirable non-uniform crystal growth, which leads to pinholes and hole-electron recombination sites. Using this method, a uniform perovskite layer that maximizes light harvesting can be readily obtained. Further, the incorporation of chloride using the HCl formulation has demonstrated to have better stability against degradation from moisture, strong solar irradiation, and high temperature.