Study Of Active Layer And Buffer Layer Modification On The Performance Of Organic Solar Cells

In recent years,bulk heterojunction(BHJ)organic solar cell(OSC)has attracted much attention due to its light weight,wide range of materials,flexible fabrication and remarkable photoelectric conversion efficiency.Recently,due to the efforts of researchers in the design of organic materials and the optimization of device structure and process,OSC has achieved more than 18%power conversation efficiency(PCE),which means that OSC has a very broad prospect in large-scale commercial applications.The structure of common organic solar cells is mainly composed of photo active layer,buffer layer and electrode.The photo active layer mainly converts the absorbed photons into carriers,while the buffer layer plays the role of collecting and transmitting these carriers.Therefore,the modification of active layer and buffer layer plays an indispensable role in improving the photoelectric performance of OSC.Based on this point,I mainly focus on the doping of active layer and the optimization of buffer layer in bulk heterojunction OSC.The main purpose is to explore new methods to improve the performance of devices.The specific content is divided into the following four parts:1.Preparation of ternary organic solar cells with iridium complex doped active layerThe ternary system BHJ OSCs can effectively broaden the absorption spectrum of the active layer and accelerate the carrier transfer rate.This work is based on the study of poly-3(hexylthiophene)(P3HT):[6,6]Bis(1-phenylisoquinoline)acetylacetonate iridium doped in binary organic solar cells with-phenyl-C71 butyric acid methyl ester(PC₇₁BM)system(Ir(piq)₂acac)was used to prepare ternary organic solar cells.The F(?)rster resonance energy transfer mechanism of iridium complex doped in P3HT:PC₇₁BM binary organic solar cells was studied.The effect of solvent evaporation annealing on the morphology of ternary active layer was also investigated.Due to the F(?)rster resonance energy transfer between iridium complex and host material,and the self-assembly effect of iridium complex on ternary mixed active layer,the energy conversion efficiency of three components doped with iridium complex is significantly increased from 2.99%to 4.44%,which is 48.5%higher than that of binary solar cells.2.Effect of photocrosslinking agent as solid additive on the performance of organic solar cellsIn order to realize the commercialization of organic solar cells,the photoelectric conversion efficiency and stability are two crucial factors.As a potential additive,solid additive can effectively adjust the morphology of active layer and optimize the performance of devices.Bifunctional Bis-benzophenone(BP-BP)was first used as solid additive in PBDB-T:ITIC active layer of non fullerene system to replace traditional solvent additive.It is found that the addition of BP-BP can optimize the?-?stacking between pbdb-t molecules,improve the surface morphology of PBDB-T films,further optimize the efficiency of exciton dissociation in the active layer,and make the carrier transport capacity more balanced.By adding appropriate amount of BP-BP,the short-circuit current and fill factor of organic solar cells were significantly improved,and the energy conversion efficiency increased from 10.61%to 11.89%.More importantly,the device optimized by BP-BP shows excellent repeatability,and its PCE is insensitive to the thickness of active layer.Finally,the thermal stability of the unsealed device based on bp-bp solid additive in air is also improved.3.Study on the mechanism of N-type small molecules as interface modification layer of high efficiency organic solar cellsThe interface contact between the metal oxide buffer layer and the active layer is an important factor affecting the device performance.For the first time,N,N-dioctyl-3,4,9,10-perylene dicarboximide(PTCDI-C8)was used as a modified layer on ZnO cathode buffer layer by vacuum thermal evaporation.Characterization of the morphology of the modified film shows that the process of preparing the active layer by solution method will not destroy the evaporated PTCDI-C8 small molecule layer,but will reduce the surface roughness of the small molecule modified layer and improve the interface contact between the buffer layer and the active layer.Furthermore,the introduction of PTCDI-C8 modified layer can reduce the work function of ZnO,improve the mobility of carriers between the active layer and the cathode buffer layer,and reduce the recombination probability of excitons from the active layer to the cathode buffer layer.Finally,PTCDI-C8 modified layer was introduced into poly[4,8-bis(5-(2-ethylhexyl)thiophene-2-yl)-benzo[1,2-b:4,5-b]dithiophene-co-3-fluorothio eno[3,4-b]-thiophene-2-carboxylate]:[6,6]-phenyl-C71-butyricacid methyl ester(PTB7-Th:PC₇₁BM)system to improve the PCE from 8.26%to 9.29%.4.Polymer modified ZnO nanoparticles as buffer layer for organic solar cellsLow cost insulating polymer polystyrene(PS)was introduced into ZnO nanoparticle buffer layer with large particle size(average particle size 60 nm)to study its effect on the film morphology and device performance.The results show that PS doping can not only improve the film quality of ZnO nanoparticles,but also form a more compact,smoother and more uniform ZnO buffer layer film;at the same time,hydrophobic PS can modify the surface properties of hydrophilic ZnO film,optimize the interface contact between metal oxide buffer layer and organic active layer.Compared with the control,the short-circuit current,filling factor and PCE of the device with PS are significantly improved.For PTB7-Th:PC₇₁BM in fullerene system and PBDB-T:ITIC in non fullerene system,the corresponding PCE increases by 18.1%and15.8%,respectively,and the device repeatability and air stability are also improved.When using flexible substrate,the device doped with PS has better mechanical durability than the device without PS.In summary,this work explored the application of functional materials in modifying the active layer and buffer layer of organic solar cells from different perspectives,and proposed a new idea to optimize the overall performance of the device.While improving the PCE of organic solar cells,we also analyzed the influence of different modification methods on devices from the aspects of film morphology,photoelectric properties and industrial production,which provided a simple and effective scheme to promote the large-scale commercial application of organic solar cells.