Research On The Impact Of Controling Vertical Phase Separation Of Active Layer On The Performance Of Organic Photovoltaic Devices

Researchers have shown significant interest in organic photovoltaics（OPVs）,alternatively referred to as organic solar cells（OSCs）,due to their properties of lightweight,flexibility,and suitability for large-area fabrication.Typically,the bulk heterojunction（BHJ）active layer of OSC devices is considered a key focus in research efforts aimed at enhancing device performance,since it plays a crucial role as the primary site for optical-to-electrical signal conversion.Recently,despite achieving a power conversion efficiency（PCE）exceeding 19%in single-junction OSCs,numerous unresolved scientific challenges persist in this field.One notable issue hindering the enhancement of OPV device performance is associated with the formation of the active layer film.Specifically,the disparate crystallization rates of donor and acceptor materials during film forming process result in unpredictable alterations for the film morphology.This,in turn,hinders the ability of the active layer to fully optimize exciton separation efficiency and minimizing carrier recombination efficiency.To tackle this issue,the proposal introduces the pseudo bilayer architecture（PBA）,a structure derived from BHJ with a vertical phase separation configuration in the active layer.This design offers a comprehensive solution by not only maximizing exciton separation efficiency through a sufficient donor-acceptor phase interface but also ensuring an excellent donor/acceptor pure phase domain.The latter facilitates the effective transmission of electrons and holes,thereby minimizing charge recombination efficiency.Despite these advantages,challenges such as the multi-step complexity,device structure restrictions,and an unclear film-forming kinetics mechanism in the preparation process of the PBA configuration active layer still require resolution.Hence,this dissertation begins by enhancing the vertical phase separation in the active layer.It investigates the connection between active layer architecture and device performance,refining the current pretreatment process,and exploring new preparation methods.Attaining precise control over the PBA based active layer preparation for both inverted and conventional OPV device offers fresh insights for developing high-efficiency OPV devices.This dissertation is primarily divided into four key aspects:（1）Study of the impact of DIO additive on the active layer morphology of fullerene based OSC.To investigate the specific influence of the pretreatment of DIO additive on the arrangement of donor and acceptor molecules in the active layer of fullerene based OSCs,this work delves into the changes in optical and electrical properties during the transition of active layer from solution to solid state.It elucidates how DIO optimizes the morphology of the PTB7:PC₇₁BM active layer.The results reveal that DIO,in collaboration with PC₇₁BM,effectively controls and enhances the aggregation conformation of the polymer donor PTB7.Additionally,the introduction of DIO induces the spontaneous enrichment and distribution of PC₇₁BM at the bottom of the active layer.This structural adjustment facilitates the fabrication of highly efficient inverted structure OSC devices,resulting in a remarkable PCE improvement from 4.74%to 7.41%（a 56.32%increase）.（2）Study of employing oscillating stratification preprocessing to create the vertical phase separation morphology of the OSC active layer.In contrast to the fullerene based OSC,there is no spontaneous gradient vertical phase separation in the non-fullerene system PBDB-T:ITIC when DIO added.To address the issue,this work introduces a novel approach for effectively preparing the PBA configuration active layer in the non-fullerene system.Leveraging the brazil nut effect,the oscillating stratification preprocessing is utilized to selectively deposit small-volume ITIC molecules at the bottom of the active layer solution.Subsequently,an ideal PBA heterojunction structure film is formed through a spin coating process.The PBA effectively enhances exciton separation,improves charge transfer efficiency,and mitigates charge recombination.The result is a significant improvement in the PCE of the inverted OSC device,increasing from 10.96%to 12.03%.（3）Study of inverted sequential deposition process to fabricate the vertical phase separation morphology of the OSC active layer.To address the challenge of the conventional sequential deposition method being unsuitable for preparing the PBA active layer in inverted structure OSC,this work enhanced the existing solution sequential deposition process.Capitalizing on the high solvent tolerance of the polymer donor material,which shields the small molecules in bottom layer from excessive erosion during the top film deposition process.This advancement enables the efficient fabrication of ideal PBA heterojunction-based high-efficiency inverted structure OSC devices.Moreover,by manipulating the film deposition sequence,the method proves effective in preparing OSCs with different structures（conventional and inverted）.The research also demonstrates the practical applicability of the inverted sequential deposition process by successfully preparing efficient PBA active layer based OSC devices with various active layer systems.Among these,the PM6:BTP-e C9 system exhibits the most notable optimization,with performance improving from14.81%to 16.09%.（4）Study of centrifugation-coating method process to fabricate the vertical phase separation morphology of the OSC active layer.To address complexities in the traditional multi-step film deposition process,this work introduced a novel centrifugation-coating method.This innovative approach applies centrifugal force vertically to the active layer film,achieving effective one-step preparation of PBA heterojunction active layers.Notably,by simply adjusting the centrifugation-coating direction,this method can prepare PBA active layers in different gradient directions,facilitating efficient fabrication of both conventional and inverted structure OSC devices.The results demonstrate significant performance enhancement in the PM6:BTP-e C9 binary conventional structure device prepared using the centrifugation-coating process,with the PCE increasing from 16.67%to 18.07%.In conclusion,this dissertation extensively investigates the control of PBA active layers through the optimization of pretreatment processes,development of novel thin film preparation methods,and conducts in-depth research on the control and preparation effects of additive,oscillating stratification preprocessing,inverted sequential deposition process,and centrifugation-coating method processes on the PBA active layer.The dissertation explores methods to optimize the morphology of the active layer and improve OSC device performance,aiming to contribute to the commercialization of high-performance OSC devices.