Study On The Influence Of Regulation Of Phase Domain Characteristics On The Photophysical Process And Performance Of Organic Photovoltaic Devices

Organic solar cells have become a strong candidate for a new generation of energy due to their easy fabrication,lightweight,low cost,and environmental friendliness.They have attracted many scientists to invest in the research field of organic photovoltaics and carry out research work.In the past two decades,fullerene materials have always been the main research system in the field of organic photovoltaics.The limitations of the materials have caused researchers to carry out in-depth research on all aspects of the properties of the materials.For example,from 2002 to 2010 alone,1,033 publications can be founded that deal with the bulk-heterojunction based on P3HT:PC61BM system.Most of them are related to the power conversion efficiency of the devices based on the P3HT:PC61BM system and involve much other research work,including standardized testing,large-area preparation,optimized device structure,and interface layer materials etc.The influence of the crystallinity and other microstructures of the material on the performance of the device was discussed in depth.Leaps and bounds have developed the research work based on the fullerene system.In recent years,with the design and synthesis of new non-fullerene materials,the efficiency of photovoltaic devices has also rapidly increased.In 2015,the ITIC designed and synthesized by Z.X.Wei et al.was extensively investigated,and the efficiency of photovoltaic devices quickly exceeded 11%.In 2021,the power convention efficiency of single-junction organic solar cells based on D18:Y6 exceeded 18%.Although the rapid development of new non-fullerene materials has promoted the rapid improvement of power convention efficiency,it has also made a relatively deficient understanding of the photophysical mechanism.It is impossible to fully understand the working mechanism of non-fullerene systems that exhibited higher performance.Meanwhile,the lack of understanding of the working mechanism limits the commercial application of organic photovoltaics.Now,the power convention efficiency more than 15%,breaking through the commercialization bottleneck,it is essential to carry out work related to the application of organic photovoltaic devices and expand the development of organic photovoltaic applications.Combining the shortcomings of organic photovoltaics with weak stability and the rapid development of the Internet of Things for a large amount of energy demand for wireless local power supply,the research work of indoor organic photovoltaics appears to be particularly important and highly feasible.Based on the above critical scientific issues,we have carried out an in-depth study of the non-fullerene system to investigate the photophysical mechanism of the effect of phase region characteristics on photovoltaic devices performance and extended the research content to the field of indoor light.The specific work content is as follows:1)The blending ratios of the donor and acceptor play a critical role in influencing the charge transfer and energy transfer of bulk heterojunction(BHJ)organic solar cells(OSC).The appropriate blend ratio for the donor and acceptor can provide the largest interface area for exciton dissociation and optimize exciton diffusion length,which helps obtain high-performance organic solar cells.Here,we have chosen a typical non-fullerene system PBDB-T:IT-M,which has been widely studied.We have deeply studied the internal relationship between the various blend ratios of donor and acceptor and the physical mechanisms of charge transfer and energy transfer.By adjusting the blending ratio for donor and acceptor,we found that the blending ratio for donor and acceptor is a critical factor in inhibiting triplet formation and recombination energy loss.The optimized blending ratio of donor and acceptor can provide a sufficient donor and acceptor interface for exciton dissociation.The detailed experimental results of time-resolved fluorescence measurement and transient absorption(TA)spectroscopy have strongly proved this point.The importance of coherence length and crystallinity are verified by grazing incidence wide-angle X-ray scattering(GIWAXS)measurement.This research work helps understand the influence of various blend ratios of the donor and acceptor on the charge transfer and energy transfer kinetics.Moreover,this work provides constructive suggestions for the rational design of new materials and the optimization of non-fullerene organic photovoltaic performance.2)Adjusting the molecular weight fraction is one of the most important strategies for optimizing the morphology of bulk heterojunction(BHJ)to obtain high-performance organic solar cells.Here,we focus on the most widely studied new non-fullerene system PM6:Y6,and in-depth study the effect of molecular weight fraction on the organic solar cell performance.With the introduction of the donor PM6 component,the fluorescence peak of the Y6 in the low energy range obviously blueshifts from 905 nm to 855 nm.The absorption and photoluminescence spectrum results show that the crystallinity of Y6 will increase,and the aggregation scale of Y6 will become smaller.To reveal the essential physical mechanism in this phenomenon,we further designed and planned experiments.First,we test the J-V curve of photovoltaic devices.We found that the open-circuit voltage increased from 0.77 V to 0.84 V with the increasing of donor components.Combined with electroluminescence and morphological analysis,it was shown that the blue shift of fluorescence spectrum could be attributable to the increase of charge transfer state and the intermolecular interaction between the donor and the acceptor,therefore causing the variation of the open-circuit voltage(VOC)in the photovoltaic device.The dark-state current analysis shows that the recombination has a weak correlation with the various blending ratio.Transient absorption spectroscopy confirmed that the optimized donor:acceptor(D:A)blending ratio can inhibit the generation of polarons and achieve high-efficiency exciton dissociation.The whole transfer process from Y6 to PM6 is an important reason to obtain more than 15%device efficiency for PM6:Y6 system.Uniform phase separation and vertical distribution can reduce the degree of energy disturbance,thereby further reducing VOC loss.The atomic force microscope and neutron reflectometer results show that a higher acceptor content can form a better vertical phase distribution,promote the formation of an ideal interpenetrating network,and thus obtain a higher fill factor short-circuit current.3)With the rapid development of non-fullerene acceptors,the efficiency of photovoltaic devices has exceeded 18%.Therefore,it is essential to carry out applied research on organic photovoltaics.It has good thermal stability,morphological stability,excellent stretchability,and mechanical durability for all polymers organic photovoltaic system.However,due to the lack of high-performance acceptor material,the research work of all-polymer organic photovoltaics is in a backward state,compared with small-molecule systems.Therefore,it is necessary to expand the research work of the all-polymer system and promote the application of organic photovoltaics under indoor light.We choose the all-polymer system PBDB-T:N2200.We systematically studied the effect of various blending ratios of donor and acceptor on the performance of the device under standard simulated sunlight and indoor light environment conditions.First of all,we characterized the basic optical information of this system with various blend ratios and found that the absorption of PBDB-T:N2200 system has a good match with the 2700K LED light source.Then a series of photovoltaic devices were prepared.The photovoltaic performance was analyzed under AM 1.5 and indoor light conditions.We found that devices with deficient content of acceptor components(2%)exhibit lower device performance(power conversion efficiency is less than 2%)under simulated sunlight light sources.However,under indoor light sources,the same devices with deficient content of acceptor components can maintain high power conversion efficiency(the power conversion efficiency exceeds 15%).To fully understand the physical mechanism of devices with deficient acceptor component content maintaining high performance,we conducted a series of discussions.First,we found that the PDBD-T:N2200 system has a better tolerance to excessive donor content.By analyzing the exciton dissociation efficiency,carrier density,and bimolecular recombination of the device with various blend ratios,we found that the device with deficient receptor content can maintain efficiency exciton dissociation carrier density,compared to the.device with the optimal blend ratio of donor and acceptor.We believe that this is why the device can still maintain good performance under deficient acceptor composition.The storage stability tests have found that the polymer system can still maintain good stability even with deficient acceptor components.