| Organic solar cells possess many advantages including abundant raw material source, simple production process and the potential to make flexible devices. It is a significant new energy resource that can be widely used in the future to relieve the energy and environmental crisis. In recent years, through the design of active layer materials and the improvement of device structure, people have been enhancing the conversion efficiency of organic solar cells constantly, and the power conversion efficiency (PCE) is up to9.2%in laboratory report. At the same time, to make organic solar cells to truly become a practical and low-cost photovoltaic technology, the conversion efficiency and the working life time must be further promoted. In the organic photovoltaic devices, the interface modification layer which connects electrode and active layer has a significant impact on the photovoltaic property and the air stability of the devices. Therefore, it is of great significance to develop the energy level-matching and process compatible interface materials to modify the deviceThe optical and electrical properties of the anode interfacial layer (AIL) with composite structure can be tuned artificially by choosing the material component and changing the ratio. Therefore, composite interfacial layer can combine the merit of each component and meet the shortfall of pure interfacial material, which have great potential in the electrode modification of polymer solar cells. In this thesis, we focus on the anode interface modification and introduce a novel MoO3-Au composite film as the anode interface layer, resulting in an improvement of photovoltaic performance and air-stability of polymer solar cells.In Chapter1, the operation principle, device structure and electrode interface engineering and the structure evolution of the interfacial material are reviewed.In Chapter2, we prepare the MoO3film by vacuum thermal evaporation and measure the work function of the film by Kelvin Probe Force Microscope (KPFM). We introduce the MoO3film into different organic solar cell systems, including 5,5’-bis{5-Octyl-2-(2,5-thiophenyl)-4H-thieno [2,3-c]pyrrole-4,6-dione}-3,3’-di-octyl silyene-2,2’-bithiophene:[6,6]-phenyl-C61-butyric acid methyl ester (DTS(TTPD)2: PC61BM) small molecule solar cell and poly(3-hexylthiophene)(P3HT):PC61BM polymer solar cell, to modify the ITO electrode and improve the hole extraction at ITO/active layer interface. Both devices show better PCE compared with the reference devices based on traditional poly(3,4-ethylenedioxy thiophene):poly (styrenesulfonate)(PEDOT:PSS) AIL.In Chapter3, we prepare the MoO3-Au composite film with different Au concentrations. We find that the conductivity increases while the transparency and the work function decrease with increasing the concentration of Au in the composite film. We choose the composite film with30%Au (weight ratio) to modify the anode interface of the P3HT:PC61BM polymer solar cell. The results indicate that the MoO3-Au composite film combines the high work function and the matched energy level of MoO3film with the high surface energy and smooth property of Au. Therefore, the MoO3-Au composite film not only guarantees a low contact resistance but also increases the shunt resistance by restraining the carrier recombination at the interface, showing better interface modification property than the pure MoO3film.In Chapter4, we investigate the influence of different anode interface layers on the air stability of polymer solar cells according to the organic photovoltaic device stability test protocol. We find that the interaction between the MoO3film and the moisture or oxygen does not change much with or without being doped with Au. The reason of better stability of MoO3-Au device can be explained as below:the Au in the composite film provides a stable route to extract and transport, thus to compensate the loss of conductivity in ambient exposure process and slow down the degradation speed. |
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