Charge Transfer Dynamics in Perovskites Crystals-Graphene Heterostructures for Light-harvesting Applications

Abstract

In the field of catalysis, optoelectronics, and energy applications heterostructures of halide perovskites and graphene are developing as favorable materials. In these heterojunctions it is significant to get insight about the understanding that governs the charge transfer dynamics between the participant of heterojunction because it directly influences the output of the optoelectronic devices. In this work, the heterojunction of halide perovskites crystals with un-functionalized and functionalized graphene are described. For this purpose, mercaptoacetic acid (MAA) functionalized CsPbBr3 nanocrystals (NCs), FAPbBr3 NCs, bare graphene, and amino acids (Alanine, Tyrosine and Cysteine) functionalized graphene are synthesized. In the heterostructure of mercaptoacetic acid (MAA) functionalized CsPbBr3 NCs and alanine functionalized graphene, the surface functionalization supports an efficient attachment of the NCs with the graphene. The use of MAA as functionalizing ligand not only passivates the surface of NCs, but it also presents the possibility of band gap tuning of NCs and further coupling with the alanine functionalized graphene. By combining the alanine functionalized graphene, the photoluminescence (PL) quenching of the NCs has been observed. The PL quenching occurs because of the photoexcited electron transfer from the CsPbBr3 NCs to the alanine functionalized graphene via type I band alignment. In the heterostructures of FAPbBr3 NCs and graphene, PL quenching of FAPbBr3 NCs with successive addition of graphene is observed. The electron transfer from NCs to graphene takes place because of formation of type-I band alignment between them. In the heterostructures of FAPbBr3 NCs and amino acid functionalized graphene, the comparative effect of different functional group moieties on charge transfer dynamics is investigated. These studies suggest that the PL quenching ability is strongly dependent on the functional group and extent of charge transfer from perovskite NCs to graphene and can greatly be improved by choosing a suitable quencher for NCs. The hole and electron accepting ability of graphene can also be tuned by varying the type of the surface moieties of the graphene. The perovskites forms type II band alignment with functionalize graphene, as a result the hole transfer takes place from perovskites to functionalize graphene. Such heterostructures possessing facile charge transfer could make efficient commercial antenna systems for solar cells and optoelectronic devices. Lastly, the fluorine doped tin oxide (FTO)/titanium dioxide (TiO2)/FAPbBr3/graphite paste based solar device is fabricated possessing 6.43% power conversion efficiency xiv with an open circuit potential of 1.47 V and external quantum efficiency of about 65%. The FTO/TiO2/FAPbBr3/Carbon/graphite sheet/water oxidation catalyst photoanode is fabricated and photoelectrochemical (PEC) water oxidation is studied. The large band gap FAPbBr3 carbon based solar devices are environmentally stable, possessing high open circuit potential of about 1.47 V, higher than the thermodynamic potential of water oxidation of 1.23 V making them suitable for PEC water oxidation agent.