The Study Of Morphology Regulation And Self-Assembly Performance Of Thin Films Based On Organic Solar Cells

Bulk heterojunction(BHJ)organic solar cells(OSCs)have become a research hotspot because of their low cost,light weight,and flexibility for large-area fabrication.In particular,non-fullerene OSCs have strong tunability in absorption spectrum and electronic energy level,constantly refreshing the highest record of power conversion efficiency(PCE)of OSCs.Compared with silicon-based solar cells,OSCs have low PCE and poor device stability.The main problem is that the carrier mobility of organic materials is too low resulting in low short-circuit current of the device.In addition,the photovoltaic performance and stability of the device depend heavily on the micromorphology of the active layer.In response to these problems,we designed star-shaped small molecule acceptors with different nuclear structures to study the intramolecular and intermolecular carrier transport characteristics and the photovoltaic stability of the device;using the supramolecular self-assembly structure function to precisely control the microstructure of the active layer,Including inter-molecular π-π stacking and molecular orientation;and the effect of morphology on the photovoltaic performance of OSCs devices is explained from the perspective of organic film self-assembly time.The main contents are as follows:(1)The photovoltaic properties of four materials,IDIC,BTTIDIC,BTTIDIC-F and Ph IDIC-F,were studied,and it was proved that the benzene molecule is more suitable for the synthesis design of star-shaped small molecule acceptors than benzotrithiophene.Compared with BTTIDIC-F,Ph IDIC-F and polymer donor form a cascade structure,which reduces the energy level loss(Eloss),so as to increase the open circuit voltage,at the same time,the photon utilization of 500-650 nm band is improved,and the short circuit current is increased;the formation of network interpenetrating structure with polymer donor is conducive to charge transmission,and the molecular arrangement is biased towards the face-on structure,which improves the vertical transport capacity of carriers;higher charge mobility,ensuring the improvement of short-circuit current.(2)We propose a novel amphiphilic small molecule DGI as an active layer additive.Based on PBDB-TF:IT-4F system,the network layered structure of DGI self-assembly induces the crystallization of small molecule acceptors,enhances the π-π orientation of the acceptor molecules,and induces the face-on orientation of the acceptor molecules,which promote the molecular mobility,reduce the recombination of carriers,the efficiency of the device is improved;the self-assembly time of DGI is short,which limits and plasticizes the phase separation of the acceptors in a short time,so as to improve the morphology stability of the active layer and the thermal stability of the device;the DGI additive has universality,The network layered self-assembly structure also has a good regulatory effect on fullerene acceptors.(3)The effect of self-assembly time of organic thin film on the performance of the device was studied.DGI additive can improve the performance of OSCs devices with chlorobenzene as the main solvent of active layer,but it has no positive effect on those with chloroform as the main solvent of active layer;DGI can reduce the self-assembly time of organic film and affect the performance of OSCs devices.Based on PBDB-TF:Y6 active layer devices,the addition of DGI additive can promote the crystallization of active layer,and the short-circuit current is improved,but the crystallization is too strong.As a result,the morphology changes seriously,the filling factor of the device is lost,and the overall performance of the device is reduced.For the active layer materials of different OSCs systems,the reasonable selection of the main solvent is very important to the performance of the device,and the main solvent determines the general time of the active layer self-assembly into the film.After selecting the suitable main solvent,the self-assembly time can be precisely adjusted by means of additives,thermal annealing and other methods to adjust the device performance.