The Study Of Morphology Control Of Porphyrin Small Molecules Based Photoelectric Devices And Ternary Solar Cells

The current energy structure has decided the society to rely heavily on non-renewable fossil fuel,and at the same time use of fossil fuel has caused serious environmental problems.The severe situation has forced us to industriously develop zero-emission clean energy.Organic solar cells?OSCs?have the advantages of lightweight,flexible,and large-area printing fabrication,which have attracted the interest of many research groups around the world.This technology is also considered to be one of the most promising solutions to solve the current energy crisis.Small-molecule solar cells are an important branch of the OSCs.Recently,the power conversion efficiency?PCE?of OSCs based on small molecules has exceeded 11%.In addition to synthesizing new small molecule materials with wide absorption spectra,strong extinction coefficients,suitable energy levels,and ordered structures,active layer morphology control during devices fabrication processing is also very important for device performance.In general,good active layer morphology not only provides sufficient interfaces for the excitons separation and carrier generation,but also facilitates effective carrier transportation.The studies in this thesis can be divided into three parts:The first one is to study the changes of optical,morphology and electrical properties of the active layer and OSCs under different processing conditions,and further reveal the relationship between active layer structure and device performance.The second part is mainly to study the ternary solar cell devices by adding the third component in the binary cell systems.The ternary cells developed from the single-layer binary cell devices can achieve the purpose of wide spectral response range and low energy loss,which benefits to the application in the future.A series of characterization methods was used to prove the effects of the third component in the ternary system on the energy level of the material,surface energy,charge transfer,FRET energy transfer,induced co-crystallization,crystal orientation,phase separation of solar cells.We also systematically explained the effects of these parameter changes on the performance of the ternary cells device.In the third part,we fabricated organic photodetectors with response to near infrared region.By reducing the noise current and enhancing the current response of the detector from the material design and device fabrication,we could fabricate photodetector device with high detectivity.The details are as follows:In the second chapter,we fabricated small-molecule solar cells based on porphyrin donor with a conventional structure,and studied the effects of thermal annealing and solvent annealing on the morphology of the active layer.Compared to the active layer without post-treatment,the porphyrin molecules in the active layer formed a closer packing when treated with chloroform solvent annealing processing.The hole mobility also showed an order of magnitude increase.At the same time,the optimized active layer has suitable phase separation scale and good phase separation purity.In the end,we obtained small-molecule OSCs with more than 10%power conversion efficiency.Furthermore,porphyrin molecules also show different molecular crystallinity and phase separation under different solvent annealing.We found that the carbon disulfide solvent treatment induces J-aggregation of the porphyrin molecule and the absorption of the film has a significant red shift.By characterizing the film morphology by GIXD,AFM,TEM and RSoXS,The porphyrin molecules packed more tightly when the active layer was treated by carbon disulfide,and the active layer formed a fibrous interpenetrating network structure.Therefore,we fabricated a solar cell device with a short circuit current larger than 22 mA cm^-2.In the third chapter,we prepared ternary solar cells based on porphyrin small molecule donor material DPPEZnP-O and polymer donor material PTB7.Although the onset absorption of DPPEZnP-O is near to 900 nm,there is an absorption valley at 550-650 nm.DPPEZnP-O and PTB7 have complementary absorption,so the absorption of the solar cells can be enhanced by preparing ternary blend films.The experimental results show that the short circuit current of the ternary cell device is significantly higher than that of the PTB7 binary devices,and the PCE of the device is dramatically increased from 7.47%to 8.39%.In addition,the fill factor of the ternary system still maintains the same level as the binary cell device,which proves that the third component does not damage the system's exciton separation and charge transfer.In the fourth chapter,we fabricated all small-molecule ternary solar cells based on two porphyrin donor materials with same molecule backbones and the optimal PCE of ternary device was 10.17%.Both short-circuit current and fill factor of the ternary device are significantly increased when compared to the binary solar cell.Although the absorption of these two porphyrin materials has no obvious difference,the two porphyrins can be fully blended at the molecule level in the ternary system because DPPEZnP-TBO and DPPEZnP-BzTBO have similar chemical structures.In addition,DPPEZnP-TBO has a higher HOMO level,so the molecule can play a role in hole transfer which improves charge transport.GIXD and RSoXS were used to characterize the blended films and the corresponding data showed the molecular packing of the ternary film mainly takes the form of DPPEZnP-BzTBO,and DPPEZnP-TBO can be incorporated into DPPEZnP-BzTBO framework without disturbing the molecular packing or resided in amorphous region to form molecular mixture when the DPPEZnP-TBO doping ratio is less than 20%.In fifth Chapter,we prepared a ternary solar cell based on a polymer donor PBDB-T and two non-fullerene acceptors ITIC and IDT-T.The PCE of the optimized ternary device was12.22%.Compared to the binary cells,the short-circuit current,open-circuit voltage,and fill factor of the ternary devices are significantly enhanced.Fluorescence spectroscopy and photoluminescence and time-resolved photoluminescence show that there is a significant energy transfer between IDT-T and ITIC,and transient absorption proves the improved hole transportation,which helps to enhance both the EQE of the device in the long wavelength region and the fill factor.At the same time,ITIC and IDT-T had a good miscibility because of their similar chemical structure which also led to co-crystallization of these two acceptor molecules.The cooperation of multi-functional IDT-T molecule in the ternary system improved the performance of the corresponding ternary cells device significantly.In the sixth chapter,the elongated conjugated length of the porphyrin and effective morphology control are useful to increase the spectral response intensity,broaden the spectral response range and reduce the dark current of the device.Therefore,we have fabricated an organic infrared photodetector with an external quantum efficiency of approximate 48.0%at850 nm,a dark current density of 4.25×10^-10 A/cm² at 0 bias voltage and a detectivity of5.73×10¹³ Jones.In addition,the detectivity of the device exceeded 10¹³ Jones in the range of360 to 950 nm.This is the best performance based on small molecule NIR photodetectors up to date.