Side chain functionalization of conjugated polymer on the modulation of photovoltaic properties of fullerene and non-fullerene organic solar cells

Abstract

We report a series of π-conjugated polymers (P1-F, P2-Cl, and P3-OMe) with three different functional groups (fluorine, chlorine, and methoxy) on their conjugated side chains. Although all three polymers showed identical photophysical properties by varying the functional group, they showed a notable difference in their dipole moment difference between the ground and excited state (Δµ_ge) values. Furthermore, photovoltaic properties of fullerene organic solar cells (FOSCs)/non-fullerene organic solar cells (NFOSCs) were significantly affected concerning the functional group in the π-conjugated polymer. Interestingly, halogen-substituted polymers (P1-F and P2-Cl) showed an enhanced PCE than methoxy-substituted polymer (P3-OMe) in both NFOSCs and FOSCs. Also, the FOSCs were much affected upon functional group modulation than did in NFOSCs. The difference in the photovoltaic properties of P1-F, P2-Cl and P3-OMe based OSCs was further analyzed by atomic force microscopy, space charge limited current method, water contact angle and transient photoluminescence measurements. Overall, our work sheds light on the importance of side chain functional group modulation of donor polymers for efficient F and NFOSCs.

Graphical Abstract

We report a series of π-conjugated polymers (P1-F, P2-Cl, and P3-OMe) with three different functional groups (fluorine, chlorine, and methoxy) on their conjugated side chains. Although all three polymers showed identical photophysical properties by varying the functional group, they showed a notable difference in their dipole moment difference between the ground and excited state (Δµ_ge) values and photovoltaic properties (fullerene and non-fullerene organic solar cells).

Supporting information

Monomer and polymer synthesis, materials and instruments, device fabrication, device measurement and characterization, schemes S1 and S2; 1H and 13C NMR of monomers (Figure S1 and S2); 1H NMR of P1-F, P2-Cl and P3-OMe (Figure S3-S5); CV and TGA of P1-F, P2-Cl and P3-OMe (Figure S6); Normalized absorption spectra of P1-F, P2-Cl and P3-OMe in chlorobenzene and film (Figure S7); DFT simulated HOMO and LUMO of P1-F, P2-Cl and P3-OMe repeating unit (Figure S8); SCLC curves of hole-only only devices of F and NFOSCs (Figure S9); Pictures of CA measurements using water and glycerol (Figure S10); PCE vs absolute difference between the donor and acceptor materials; PCE vs χ (Figure S11); Summary of ground state dipole moment; excited state dipole moment; dipole moment difference between the ground and excited state of polymers (Table S1), SCLC hole mobility of optimized NFOSCs and FOSCs (Table S2); Transient lifetime values of the pristine polymers and their optimized blends. (Table S3); contact angle and surface free energy of donor polymers and acceptor materials (Table S4); Flory-Huggins interaction parameter (χ) obtained from the SFE (Table S5).