Performance enhancement of perovskite solar cell with graphene nanofibers
Yun Li a, Wallace Woon-Fong Leung a
a The Hong Kong Polytechnic University, Hung Hom, Hong Kong, Hong Kong, Hong Kong
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Poster, Yun Li, 197
Publication date: 11th February 2019

Although the application of graphene-derived nanomaterials in the electron transport layer (ETL), hole transport layer (HTL), or top electrode of perovskite solar cells (PSCs) has been thoroughly studied, the effects of inserting such materials into the perovskite layer of PSCs is not well understood. In this study, pristine graphene nanofibers were introduced into the perovskite layer of PSCs. The quality of the electrospun graphene nanofibers was optimized by controlled centrifugation of gra-
phene sheets in the precursor suspension. Under optimized conditions, the device power conversion efficiency increased from 17.51% without graphene to 19.83% with graphene nanofibers, representing a 13% increase. The introduction of graphene nanofibers into the perovskite layer led to a dramatic increase in the grain size of the perovskite layer to over 2 micrometers, owing to improved nucleation and crystallization at the nanofiber interface, which led to much higher FF and Jsc values. The significant increases in Jsc and Voc are attributed to the improved charge-transport properties of the graphene nanofibers with superb charge conductivity introduced into the perovskite layer. The latter was independently verified by the measured electron transport time. The stability of the device was also improved. In summary, an effective approach has been developed to improve the performance of PSCs by using pure graphene nanofibers.

On another aspact, we fabricated a thin and structured TiO2 nanofibers embedded with graphene layer as the scaffold layer for the perovskite soalr cell. The structured scaffold facilitates nucleation from the nanofibers, especially at the intersections of nanofibers. By orienting the fibers and controlling the fiber packing density with uniform openings, large uniform crystals with high crystallinity that has high light absorption can be obtained. Further, graphene sheets in roll-up form, to eliminate adverse edge effect, were inserted in the TiO2 nanofibers in a convenient, simple way to enhance charge conductivity of the semiconductor nanofibers. The concentration and size of graphene that has been incorporated in the TiO2 nanofibers have been optimized by controlled centrifugation on the graphene sheets in the precursor suspension prior to electrospinning to form nanofiber scaffold. The optimized PSC device exhibited 19.30% power conversion efficiency (PCE) (with open circuit voltage Voc 1.08 V, current density JSC 24.06 mA/cm2 and fill factor FF 0.75, respectively), which is 11% higher than the device without the nanofiber scaffold with PCE of 17.46%.

The use of Dr. Gang Li’s facility in fabricating the counter-electrode is acknowledged. We also acknowledge the Mechanical Engineering Department of HKPolyU for providing the studentship for Yun Li. We also acknowledge the funding support, in part, from the Central Research Grant project at HKPolyU with account G-YBL1 on Charge transport in perovskite solar cell

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