Interface Design And Performance Study Of Organic Photodetectors And Solar Cells

Organic photodetectors and solar cells have been attracting a lot of attention due to their inherent advantages,such as easy manufacturing,light weight and solution processable.This thesis focuses on efficient organic photodetectors and flexible solar cells via interface design.Main research results are presented as follows:First,the vacuum evaporation of metal electrode will typically lead to the doping of the active layer at the interface,resulting in the photodetectors with high dark current.To solve the issue,transfer printed conductive polymer PEDOT:PSS electrode was used to replace the metal electrode.The PEDOT:PSS top electrode can circumvent the doping from the metal electrode.Under operating bias of-0.2 V,the photodetector with PEDOT:PSS electrode shows the comparable photocurrents,while exhibits over two orders of magnitude lower dark current density than the photodetector with metal electrode.The highest detectivity of photodetector is over 10¹³ Jones.At the same time,PEDOT:PSS electrode has high transmittance,which is able to act as a double-side responsive photodetector.Second,reverse injection of electrons/holes is critical to the device performance.The insertion of blocking layer is an effenctive strategy to solve the problem.However,the requirement of orthogonal solvents between active layer and blocking layer limits the development of blocking layer materials.Transfer printing technology is utilized to fabricate the blocking layer and achieve the photodetector with low dark current,high detectivity.Transfer printed electron blocking layer not only blocking the doping from metal electrode and electron reverse injection,but also alleviate the repuirements of orthogonal solvents.Photodetectors with P3HT electron blocking layer show noise current as low as 10^-14 A/Hz^1/2.The prepared P3HT electron blocking layer can be applied to various organic photodetectors based on different active layer.Third,single-junction and tandem structure solar cells have been reported in the literature.The device with two-junction layers is rarely reported.Processing compatibility,including orthogonal solvents for two heterojunction layers and processing temperature for different layer,is the limitation to realize two-junction layer device.The transfer printing technique can avoid the interaction between two heterojunction layers,which provide the possibility to realize two-junction device.It is found that the photo-generated voltage and EQE response spectra of two-junction layer device are closely related to the stacking sequence and the acceptor of two heterojunction layers.The new physical phenomenon provides a new route for the design of photodetectors.Fourth,solution-processable high-efficiency interface layer is the key to realize high efficiency and flexible organic solar cells.PEIE is widely used as high efficiency and low temperature processable interfacial layer.However,the amine of PEIE will react as a nucleophile with the C=C linkage moiety between donor unit and acceptor unit in nonfullerene materials through the Michael addition reaction.The reaction will destroy the chemical structure of nonfullerene materials,resulting in poor efficiency and“S”shape in J-V curves.To solve the problem,a strategy of protonating amine group was proposed to passivate the reaction between the non-fullerene material and the PEIE interface layer.Based on protonated PEIE,the flexible non-fullerene solar cell can be realized at room temperature.The solar cell shows high efficiency of 12.5%.