Studies On High-efficiency Organic Solar Cells Prepared With Non-halogenated Solvent And Blade-coating

Organic solar cells(OSCs)have attracted extensive attention over the past two decades due to their superior flexibility,light weight,low cost,and roll-to-roll solution processability.At present,the power conversion efficiency(PCE)of OSCs has exceeded 19%benefitted from the development of high-performance organic photovoltaic materials and precise morphological control of the active layer.However,the most high-efficiency OSCs were obtained with toxic halogenated solvents and the easy-to-operate small-area spin-coating method,which makes it difficult for the OSCs to meet the needs of large-area continuous and environmentally friendly production in future applications.Therefore,it is necessary to develop novel strategies for the fabrication of OSCs with environmentally friendly non-halogenated solvents and largearea zone-casting or blade-coating technology,so as to facilitate the development of organic photovoltaic industrialization.However,the donor:acceptor blend active layer prepared with non-halogenated solvent and blade-coating is easy to form large phase separation and weak molecular crystallization and orientation due to the poor solubility of non-halogenated solvents to the commonly used efficient donors/acceptors and the relatively slow film-drying dynamics of the blade-coating.It is not conducive to the efficient dissociation of excitons and the transport of free charges,and greatly limits the improvement of the performance of OSCs prepared with non-halogenated solvent and blade-coating.To tackle this issue,this paper focuses on regulating the film-forming kinetics and thermodynamics process of the active layer prepared with non-halogenated solvent and blade-coating through the processing temperature,non-halogenated additives,layer-bylayer(LBL)blade-coating and ternary strategy,towards promoting the formation of nanofiber-like phase separation and high crystallization and orientation of donor and acceptor molecules in the active layer,and finally leading to the enhanced photovoltaic performance of the devices.The corresponding mechanisms of proposed regulation strategies were studied in detail,and the correlation among the regulation strategyactive layer morphology-device performances was constructed.Finally,large-area photovoltaic module devices were fabricated by using the developed strategies to explore their potential application in the manufacturing of large-area OSCs.The specific achievements are as follows:1.The effects of blade-coating temperature and additive 1,2-dimethylnaphthalene(DMN)on the morphology of the bulk heterojunction(BHJ)PM6:Y6 active layers and the device performance of resultant OSCs prepared by non-halogenated solvent and blade-coating were studied,and the related mechanism was explored in detail.It has been disclosed that high-temperature blade-coating can effectively suppress the excessive aggregation of acceptor Y6 and enhance the orderly stacking of Y6 acceptors in the BHJ PM6:Y6 active layer by accelerating the film-drying process.The highboiling point non-halogenated additive DMN can induce BHJ PM6:Y6 to generate more nucleation sites and increase the crystallinity of PM6 and Y6 by extending the crystal growth time during film-drying process.The active layer is promoted to form a high-quality interpenetrating PM6:Y6 blend morphology with nanofibrous phase separation and highly crystalline morphology of donor/acceptor,leading to increased charge generation,migration and collection efficiency.As a result,the PCE of the resultant OSCs is increased from 5.55%to 15.51%.The correlation between the processing strategy,the donor:acceptor blend morphology and the photovoltaic performance was established.Finally,the large-area(28.82 cm2)and high geometric fill factor(GFF,93.3%)OSC module was fabricated by using the developed strategy in the ambient condition,and a PCE of 11.24%was achieved.2.The effects of additive DMN on the active layer morphology and the device performance based on the LBL blade-coated PM6/Y6 active layer with nonhalogenated solvent were studied in detail.The in-situ absorption spectra of the bladecoated active layers show that the addition of non-halogenated solvent additive DMN in the upper layer of Y6 solution induces two-time nucleation and crystallization processes of Y6 molecules during the film-drying.The increased nucleation sites can effectively inhibit the excessive aggregation of Y6 molecules in the LBL blade-coated PM6/Y6 active layer,and the prolonged crystallization time improves the face-on crystallization and orientation of Y6 molecules in the active layer,promoting the formation of nanofibrous phase separation and high donor/acceptor crystal morphology in the LBL blade-coated PM6/Y6(o-XY+DMN)active layer.Such kind of active layer morphology accelerates the dissociation of excitons and the transport of charges and inhibits the charge recombination,finally increasing the PCE from 12.76%to 16.15%.The relationship between the processing strategy,active layer morphology and the photovoltaic performance was established.Finally,the OSC modules with an effective area of 28.82 cm2 and a high GFF of 93.8%were prepared with the non-halogenated solvent and LBL blade-coating strategy in the ambient condition,and a PCE as high as 12.64%was achieved.3.The effects of a third component IT-M on the PM6/BTP-eC9 active layer morphology and the device performance prepared with non-halogenated solvent and LBL blade-coating strategy were studied in detail,and the related mechanism was explored.The experimental results show that the LBL blade-coating improves the vertical distribution of donor and acceptor components in the PM6/BTP-eC9 active layer,leading to improved charge extraction efficiency of the device.The introduction of the third component of IT-M in the underlying PM6 attenuates the damage of the upper layer of BTP-eC9 acceptor molecule to the crystalline PM6 zone in the underlying film during LBL blade-coating due to different intermolecular interactions,leading to the dense nanofiber-like phase separation morphology.The IT-M molecules are inclined to reside at the interfaces of PM6 and BTP-eC9 according to the calculation of the wetting coefficient,and thus a cascade energy level alignment for the three materials is formed,which is favorable for fast charge-transfer process.The improved active layer morphology and the charge-transfer bridge of IT-M at the donor PM6acceptor BTP-eC9 interfaces reduce the charge recombination.Lower energy loss(Eloss)and higher open-circuit voltage(VOC)are achieved that further improves the PCE of the devices from 16.38%to 17.16%.The relationship between the ternary strategy,LBL active layer morphology and device performance was established.Finally,the ternary OSC modules with a large area of 28.15 cm2 and a high GFF of 93.6%were prepared with non-halogenated solvent and LBL blade-coating and without any additives and post treatment in the ambient condition,and a PCE as high as 14.20%was obtained.