Photodetectors Based On Organic/inorganic Hybrid Perovskites

Organic and inorganic hybrid perovskites(e.g.,CH3NH3PbI3),have the advantages of simple fabrication process,tunable bandgap,long exciton diffusion length,high charge carrier mobility,and have emerged as a promising optoelectronic semiconductors for various applications.The efficiency of perovskite solar cells has excess 20%after only ten years of active research.The perovskites also have the advantages of high defect tolerance and long carrier lifetime,and has been regarded as one of the ideal materials for photodetectors.In this thesis,high performance perovskite photodetectors have been fabricated through designing new device structure with a CH3NH3PbI3 material as the active layer.The results are enclosed as follow.High performance SnO2/CH3NH3PbI3 heterojunction perovskite photodetectors are demonstrated by a fully solution method.The optimized photodetector exhibits a responsivity of 1.65 A/W,which is more than twice to the reference device with a pristine CH3NH3PbI3 layer on bare glass.Besides,the device also exhibits a fast reponse speed with rise and decay times both of about 10 ms.The inserted SnO2 layer not only improves the morphology and crystallinity of the CH3NH3PbI3 films,but also increases the dissociation efficiency of the excitons in CH3NH3PbI3 through electron transfers from CH3NH3PbI3 to SnO2,which suppresses the charge carrier recombination probability of the devices and hence increasesthe performance perovskite photodetectorsA hybrid planar-mixed heterojunction photodetector with a structure of SnO2/CH3NH3PbI3:PC61BM is constructed.Such a photodetector can be fabricated by spin-casting a CH3NH3PbI3:PC61BM bulk heterojunction on a planar SnO2 layer.The photodetector with an optimized PC61BM doping concentration shows a responsivity of 9 A/W,which is more than three times to that device without a PC61BM doping or a planar SnO2 layer.It is found that the introductions of PC61BM can not only manipulate the growth process of the CH3NH3PbI3 film and form a more compact layer,which decreases the grain boundary and increase the charge carrier mobility,but also passive the defect states on CH3NH3PbI3 and decrease the charge carrier recombination probability.On the other hand,the SnO2 and PC61BM can act as the electron acceptors from CH3NH3PbI3,which boosts the dissociation efficiency of the excitons formed in CH3NH3PbI3 under illuminationPhotomultiplication is demonstrated in an inverted hole transporting layer-free perovskite photodetector with a structure of ITO/CH3NH3PbI3/C60/Bphen/Ag.The photomultiplication disappers when a PEDOT:PSS layer is added as the hole transporting layer.This indicates that the photomultiplication is related to the ITO/perovskite interface.The photocurrent amplification is attributed to the accumulation of holes and positively charged CH3NH3+ and I vacancies at the ITO/perovskite interface,which dramatically lowers the electron injection barrier.