Manipulating Active Layer Morphology And Interface Structure Of Organic Solar Cells

With the continuous development of the economy,human dependence on natural resources is increasing,and clean renewable energy,led by solar energy,has attracted increasing attention.Organic solar cells have good application prospects in the fields of solar cell due to their advantages of light weight,good flexibility,simple preparation process,and easy realization of large-area processing.However,the further improvement of the performance of organic solar cells is constrained by some technical factors.Two aspects of the active layer morphology and interface layer can not be ignored.In the research of this dissertation,we prepared photovoltaic devices based on classical donor and acceptor materials PTB7 and PC71 BM.Their film on organic photovoltaic devices was measured by atomic force microscopy(AFM),transmission electron microscopy(TEM)and X-ray diffraction(XRD).Film morphology and interface properties are regulated and systematically studied,and the performance of the device is optimized based on the obtained microscopic rules.The main achievements of the dissertation are as follows:1.The effect of the dibromoalkane chain length on the morphology of active layer films and the performance of organic photovoltaic devices was investigated.The use of solvent additives optimizes the morphology of the active layer,which increased the short circuit current(Jsc)and open circuit voltage(Voc)of the photovoltaic device.First,dibromoalkane additives with different alkane chain lengths were selected to study the effect on the performance of PTB7:PC71BM photovoltaic devices to reveal the relationship between solvent additive properties,active layer morphology,and photovoltaic performance.Among these additives with different chain lengths,the introduction of 1,4-dibromobutane(DBB)with a moderate chain length showed the highest photovoltaic performance,and the photoelectric conversion efficiency(PCE)increased from 3.57% without additive to 5.53%,PCE increased by 55%.Systematic studies on solvent properties,film morphology,and structure formation mechanisms have shown that the introduction of DBB additive helps to form both nanoscale phase separation morphology and a pure PTB7 phase region.The former is conducive to the effective dissociation of excitons and the latter to carriers.Transmission provides a powerful charge transfer channel.2.Systematic study of the effect of aromatic solvent additives with different substituent groups on the performance of organic photovoltaic devices.The film formation kinetics of PTB7:PC71BM system was controlled by controlling the type of substituents,and the components were rapidly cured before PC71 BM components formed large-scale aggregates,thereby achieving the optimization of the active layer.First,using the boiling point difference between the solvent molecule and the main solvent CB,we divide the solvent additives into two major categories:(1)having a similar boiling point with the main solvent;(2)having a solvent boiling point higher than that of the main solvent.Then we compared these aromatic solvents with different substitution groups in the PTB7:PC71BM system and conducted a comparative study.It was found that the PC71 BM phase is difficult to form a more continuous crystalline phase region when the film was formed rapidly,so the carrier transport process was suppressed to a certain extent,the corresponding device efficiency has also been reduced.The introduction of the second type of additives can reduce the solvent evaporation rate,prolong the film formation time,and inhibit the formation of large-scale aggregates of PC71 BM components,thus producing more donor/acceptor blended phases and better device performance.3.Systematic study of the influence of organic cathode interface layer on the performance and stability of organic photovoltaic devices.Alq3,BCP,and Tm Py PB are commonly used as electron transport materials in the OLED field.We have applied them to organic solar cells P3HT:PC61BM,PTB7:PC71BM systems.It was found that the introduction of the organic interface layer can effectively improve the device performance and stability.Among them,the introduction of Tm Py PB in the PTB7 system makes the PCE reach 7.96%,which is mainly due to the rough surface morphology of the organic/metal interface to generate more defect states,which is conducive to electronic extraction,higher electron mobility and comparison Deep HOMO levels favor electron transport and hole blocking.The combination of the Li F and Tm Py PB dual electron transport layer further enhances the hole blocking capability to suppress charge carrier recombination and protect the active layer from damage from the surrounding environment,further improving device performance(8.01%)and stability.