The Study On Device-performance Of Organic Solar Cells With Novel Interfacial Materials

As a new generation of energy conversion technology,organic solar cells（OSCs）have drawn much attention due to their potential of flexible processing and large-area production.The key to their commercial production lies in the combination of materials and technology used in small-area devices with roll-to-roll（R2R）coating processes for large-area OSC modules.However,most interfacial materials have very poor translation efficiency when they are used in the fabrication of large-area OSC modules.To meet the technical requirements of R2R printing processes,new interfacial materials that can work efficiently in thick condition should be developed.Another strategy is to develop a new coating technique with uniform thin film,to avoid the inferior roughness problem in large-area production.Our research works in this thesis are mainly focus on thickness-insensitive interfacial material and new coating technology for the preparation of large-area interlayer.In the first part,we employed chitosan,the environment-friendly and abundant biomass material,and its derivatives as cathode interlayer materials in inverted OSCs by using electrostatic Layer-by-Layer（eLbL）self-assembly technique.Using spin coating technique,it is difficult to obtain uniform thin films with full surface coverage,which make chitosan can not reach the optimal performance as cathodic interlayers.The eLbL self-assembly technique was a suitable strategy to obtain continuous films with full surface coverage and controlled thickness under nanometer scale.What’s more,due to the highly ordered LbL structure,both interfacial dipoles and molecular dipoles were formed and utilized to decrease the work function of ITO electrodes.With optimized chitosan eLbL films as cathode interlayer,inverted OSCs with thick active layer exhibited a PCE of 10.18%.These indicated that eLbL self-assembly is an efficient method to fabricate high-performance cathode interlayer.The second part studies the preparation of ZnO films with orderly microstructure and optimized morphology by using eLbL self-assembly technique.The ZnO nanoparticles wrapped by cationic surfactant and anionic polyelectrolytes PFCOONa were combined together to form cathodic interlayers for polymer solar cells.By this means,the voids of ZnO films could be filled by polyelectrolytes,and the defects of ZnO nanoparticles were passivated.Applying the eLbL layers to polymer solar cells with PTB7-Th:PC₇₁BM yielded a PCE of 9.25%,exceeding the efficiency of ZnO interlayers formed by spin coating.The results suggested that eLbL self-assembly technique provide a new solution for the preparation of interlayers with nanoparticle for polymer solar cells.In the third part,a new thickness-insensitive electron-transport layer（ETL）with enhanced electron-extraction and electron-transport properties for high-performance OSCs was reported.With the incorporation of Cs₂CO₃ into the PF6NPSBr ETL,the PCE of resulted OSCs was significantly enhanced due to the favorable interfacial contact,energy-level alignment,and thus facile electron transport in the OSC devices.These hybrid ETLs also exhibited high transparency and high electron mobility,which make them suitable for novel thickness-insensitive ETLs and avoid the parasitic absorption of ETL itself simultaneously.A notable PCE of 10.78%was achieved with the thick active layer PTNT812:PC₇₁BM.These findings indicated that doping alkali salt into organic interfacial materials can be a promising strategy to design efficient and thickness-insensitive ETL.In the fourth part,we focused on the prepatation of metallic two-dimensional（2D）ordered pattern,which can be used for transparent electrode of OSCs and be embedded in the interlayer of OSCs for plasmon resonance effect.Using air-water interface self-assembly,PS nanospheres can form 2D monolayer with tightly closed structure,which can be applied as a template to fabricate hexagonal patterns.The surface coverage of metallic porous films can be adjusted by plasma etching of PS monolayer and changing the original size of PS spheres.Finally,the porous films were applied as transparent electrodes in OSC devices,and achieve a maximum PCE of 6.52%.Plasmon resonance effect of metal nanoparticles mostly depends on the size of the particles and the distance between them.The hexagonal pattern fabricated by template lithography,can precisely control the distance between the metal nanoparticles,which is an effective method to prepare the metal particles with enhanced plasmon resonance effect.We need more follow-up work to explore its principles and functions.