Miscibility Matching Strategy Regulating Crystallization And Phase Separation Of Active Layer In Ternary Organic Solar Cells

The crystallization and phase separation structure in the active layer of organic solar cells(OSCs)is relating to the power conversion efficiency(PCE).How to char-acterize and analyze the crystallization and phase separation of the active layer remains to be a huge challenge.This article aims to improve the PCE by adding the third component into the classic and highly efficient binary system to modulate the crystallization and phase separation.By investigating the miscibility matching between the third additive and donor and acceptor,the novel idea to choose the appropriate third component will be affored.First,the small molecule DRCN5T was added into PTB7-Th:PC71BM system.By calculating the miscibility between different components,it is found that the miscibility between DRCN5T and PTB7-Th is good to be able to form a homogeneous phase.The poor miscibility between DRCN5T and PC71BM leads to phase separation in the active layer.The strategy of adding a third component optimizes the active layer morphology of the system and improves the charge transport mobility.Therefore,the PCE of the device increased from 10%to 11.1%.Then,in the PBDB-T:ITIC system,the third components of PDCBT and P3HT were added.By calculating the Flory-Huggins interaction parameter,it is found that the PDCBT and P3HT is miscible with PBDB-T.A small amount of PDCBT and P3HT could be able to form the bimolecular crystallization.However,the miscibility between the third additive and ITIC acceptor is different.For example,PDCBT and ITIC is immiscible,leading to obvious phase separation.In contrast,P3HT and ITIC is observed to be miscible,affording a homogeneous morphology in the P3HT:ITIC blend.Due to the difference in miscibility between the two type third additives and donor and acceptor,the performance of solar cells exhibited of difference.The PDCBT could optimize the morphology of active layer,enhancing the charge mobility.The PCE of the devices increased from 9.40%to 10.97%.In contrast,the incorporation of P3HT into PBDB-T:ITIC led to the serious depression of PCE value.Finally,according to the physical phenomenon that the conjugated polymers could form the bimolecular crystallization,the P3BT and P30T showing of different side chain length were mixed with PBDB-T to afford blends with different weight ratio.By calculating the miscibility and Gibbs free energy,it is found that both of P3BT and P3OT could form bimolecular crystallization with PBDB-T.The grazing incidence X-ray scattering results indicate that the P3OT with longer side chain could form bimo-lecular crystallization with PBDB-T in a wider range of mass ratios.The side chain length influencing the bimolecular crystallization was discussed in detail.