Study On The Fabrication And Performance Of Organic Solar Cells Based On The Modified ZnO Interlayer

Organic solar cells?OSCs?have recieved extensive attentions due to their advantages of light weight,flexibility,low cost,and capable of solution processable.Until now,the main research focus of this OSCs technology is still to improve the power conversion efficiency?PCE?and stability?lifetime?,as which is the key factor limiting their practical application.To achieve high efficient and stable organic photovoltaics,the interfacial materials have played an indispensable role.As one of the most commonly used and classical cathode interlayers?CILs?,ZnO possesses many characteristics such as various preparation method,high chemical stability and transparency,suitable LUMO energy level and good electron transporting ability.However,the ZnO CIL has some problems as well.On one hand,the surface of ZnO synthesized by the solution method usually exsits traps,leading to the undesirable charge recombination.On the other hand,the performance of currently reported OSCs is very sensitive to the ZnO CIL thickness.In addition,relevant work about the regular structure OSCs with high efficiency and high stability at the same time is rarely reported.Based on these,this thesis focused on the classical ZnO CIL,and aimed to improve its interfacial properties and device performance through surface modification or doping.The main content can be summarized as follows:?1?ZnO nanocrystals were synthesized by a facial solution method.To passivate the surface defects of ZnO and improve the interfacial properties,a thin biological film of light-harvesting pigments complexes?LHCII?was modified on the ZnO film surface,resulting in a huge enhancement of the photovoltaic parameters.The device PCE based on ZnO/LHCII stacked interlayer raised up to 9.01%from 8.01%?pure ZnO-based OSCs?.With LHCII modification,the ZnO CIL showed better affinity to the atctive layer,benefiting the film quality.Moreover,the Zn O/LHCII CIL provided matched LUMO level and favourable interface dipoles,thus increasing the built-in potential and electron transporting,hence improving the device performance.The results indicated that the environment-friendly bio-protein materials can be successfully applied into the OSCs devices with improved performance,and also expand the selectivity of organic photovoltaic materials.?2?As to the issue that the OSCs performance is sensitive to the thickness of interfacial layer,an aluminum-doped ZnO?AZO?CIL material was developed,which made the OSCs possess decent device performance with AZO CILs in the wide thickness range of 6-120 nm.The AZO nanocrystals synthesized with ethanolamine as the ligand had an average size of⁵ nm and were indexed into wurtzite structure.Based on this AZO CIL?10 nm?,the PTB7-Th:PC₇₁BM inverted device obtained a best PCE of 10.42%.When the thickness was increased to 120 nm,the device still presented a PCE of 8.85%,while the PCE of the ZnO-based device was only 7.79%.Mainly due to the incorporation of Al,the AZO CIL possessed a higher conductivity and electron transporting ability,and formed a unique texture morphology in the case of thick film.The AZO-based devices also exhibited excellent storage stability.In addition,the flexible devices on PET/ITO substrate obtained a PCE of 8.93%and showed excellent mechanical stability by antibending test,remaining 88%of its initial value after 500 bending cycles.?3?A kind of AZO nanocrystals without ligand was synthesized by alcoholysis,and the regular structure OSCs with both high efficiency and stability were successfully constructed without any post-treatments such as thermal-annealing.With PTB7-Th:PC₇₁BM as active layer,a highest PCE of 10.14%was obtained for the AZO-based regular OSCs,while the PCEs of the reference devices without CIL?w/o?and with trifluoroethanol?TFE?treatment were only 6.38%and 7.81%,respectively.The results indicated that this AZO CIL not only can improve the interface contact property,avoid the direct contact between the active layer and electrode,and also can increase the built-in potential,the electron transporting and collecting efficiency,reduce the charge recombination at the interface,thus leading to greatly improved photovoltaic performance.Meanwhile,the AZO CIL played an important role as a protecting layer to block moisture and oxygen attack,so that the device achieved much better air stability than the ones of w/o,TFE,PFN and Ca CILs.In addition,the universality of AZO CIL was demonstrated in other regular OSCs with different active blend systems and could achieve excellent device performance.Especially,in PBDB-T:ITIC non-fullerene system,a champion PCE of 10.62%was realized.