Conjugated Polymer And Fullerenes Serving As Compatibilizer Optimizing Active Layer Morphology In Organic Solar Cells

In recent years,organic solar cells?OSCs?have attracted considerable attention due to their unique advantages in fabricating lightweight and flexible devices suitable for roll-to-roll technology,organic solar cells.How to further improve the power conversion efficiency?PCE?of OSCs has become a focus of attention.The incorporation of third polymer into the binary systems to fabricate ternary all-PSCs is recognized to be effective to further improve PCE values.However,the mechanism of how the third component influences the morphology evolution of active layer remains to be unknown.This article aims to analyze the mechanism of the influence of the third polymer on the morphology evolution of active layer from the miscibility viewpoint,then to have a deeper understanding of the relationship between structure-compatibility-morphology-performance.We hope can provide a reference for how to select a suitable third component to improve the PCEs of the ternary OSCs.First,the J71 was incorporated into the PBDB-T:PNDI-2T-TR?5?system to afford a ternary all-polymer solar cell.It is observed that J71 could provide complementary absorption in addition to formation of cascade energy level alignment with other polymers,which can facilitate charge separation and transport.The emission band of J71 overlaps with the absorption band of PBDB-T,indicating that a F?rster resonance energy transfer occurs from J71 to PBDB-T.By the combination of dynamic mechanical analysis?DMA?and differential scanning calorimetry?DSC?techniques,the miscibility in J71:PNDI-2T-TR?5?blend is better than that in PBDB-T:PNDI-2T-TR?5?blend according to Fox equation analysis,showing of Flory-Huggins interaction parameters of-1.003 and 0.006,respectively.Therefore,J71 could serve as an interfacial compatibilizer to optimize the interaction between the donor and the acceptor,leading to the enrichment of PNDI-2T-TR?5?on the film surface due to much lower surface energy of PNDI-2T-TR?5?.The optimized vertical distribution of PNDI-2T-TR?5?with enhanced crystallization could be further demonstrated by atomic force microscopy?AFM?and grazing incidence wide-angle X-ray scattering?GIWAXS?results.Therefore,add an appropriate amount of J71 can facilitate the electron transfer and collection in the normal device structure by affecting the morphology,thereby improving the photovoltaic performance of the all-polymer solar cell system,making the maximum PCE of 9.12%.Then,PC₆₁BM,PC₇₁BM and ICBA,the fullerene derivatives with different structures,were introduced into the PDCBT:ITIC system to explore the crystallization of the active layer,the effects of acceptor aggregation and the phase separation of the active layer.Through analysis of the basic characterization,we can find that both of PC₆₁BM,PC₇₁BM and ICBA have UV-visible absorption in the short-wavelength range of the visible light region,which complementarity with the polymer/small molecule system absorption.At the same time,the results of atomic force microscopy?AFM?and differential scanning calorimetry?DSC?tests show that the addition of the third component fullerene derivative reduces the crystallinity of PDCBT:ITIC while inhibiting the small molecule ITIC.It reduces the size of the acceptor aggregation and increases the charge transport efficiency,and the increased contact interface can make excitons separate better.The fullerene derivative acts as an isotropic charge transport carrier for good charge transfer and improves device performance.After adding a suitable ammont of ICBA as a third component into the PDCBT:ITIC system,the device PCE increased from 8.84%to 9.36%.