As an emerging clean energy technology, polymer solar cells (PSCs) have attracted wide attention in recent years because of their advantages of translucency, flexibility, and large area fabrication. In the past three years, n-type organic semiconductors (n- OSs) have been booming in high-performance PSCs as non-fullerene (NF) receptors, because n-type organic semiconductors have a wide range of precursors, low preparation costs, and absorption compared to conventional fullerene derivatives. With adjustable energy levels, low energy loss, and superior stability in morphology. To date, single junction NF-PSCs have achieved 11-13% power conversion efficiency (PCEs). When blended with wide bandgap polymers, IT - 4F-based PSCs show up to 13.1% PCE. Because of well-matched polymer donors and n-OS receptors play a crucial role in obtaining efficient PSCs, a wide range of synthetic changes (such as atom substitutions) , Side chain modification and introduction of aromatic fused rings were used to optimize high-performance polymer donors. Among them, atomic substitution, especially fluorine (F) atoms, has replaced hydrogen atoms and attracted widespread attention, and was obtained in molecular design. Wide range of applications
'Introduction to achievements'
Recently, Prof. Zhang Maojie (Corresponding author) from Suzhou University published a paper on NanoEnergy titled: 'Chlorine substituted 2D-conjugated polymer for high- performance polymer solar cells with 13. 1% efficiency via toluene processing'. The researchers designed and synthesized A new type D-A two-dimensional conjugated polymer PM7 containing thiophene benzodithiophene (BDT-2Cl) donor units and benzodithiophene-4, 8-dione acceptor units Compared with PBDB-T, a chlorine-free substituted control polymer, PM7 has a lower HOMO level, higher absorption coefficient, stronger crystallinity, and higher carrier mobility. In addition, PM7 is When the non-halogenated solvent toluene is used as a solvent, the donor, IT-4F acceptor is used as a solvent, and a high open-circuit voltage of 0.28V is obtained, while a short-circuit current density of 20.9mA·cm-2 is used, and the fill factor (FF) is For the 71.1%, a 13.1% energy conversion efficiency (PCE) was achieved. Under the same conditions, the PBDB-T:IT-4F system PSC only performed at a low Voc of 0. 67V. 5.8% of low PCEs. 13.1% of PCEs are so far reported as non-halogen solvents for photovoltaics One of the highest energy conversion efficiency of the device. These results indicate that chlorine-substituted material is a polymer photovoltaic simple and effective strategies to design high performance conjugate.
'Tutorial Reading'
Figure 1. Synthetic diagram
(a) PM7 synthetic route;
(b) The HOMO and LUMO electron distributions and energy levels calculated from the B3LYP/6–31G* (d, p) DFT;
(c) Absorption spectra of monomers in a solution of 1 x 10–5 M toluene;
Figure 2. Molecular energy level structure
(a) Molecular Structure
(b) Absorption spectra of polymer donors and non-fullerene receptors IT-4F;
(c) Molecular energy level diagrams of polymer donors and non-fullerene receptors IT-4F;
Figure 3. Photovoltaic performance test
(a) J-V curve at a 5G light source (100 mWcm-2);
(b) PM7: EQE curves of PSCs prepared by IT-4F blending;
(c) PM7: trend graph of the relationship between the thickness of active layers of PSCs prepared by IT-4F and PCE;
(d) JphvsVeff;
(e) PM7: Variation of Voc with light intensity in PSCs prepared by IT-4F blending;
(f) PM7: Changes in light intensity of Jph in PSCs prepared by IT-4F blending;
Figure 4. Two-dimensional GIWAXS characterization
(a) Two-dimensional GWIax profile of pure polymer and related blend membranes and corresponding (b) IP and (c) OOP cuts;
(d) RSoXS scattering distribution of the blend membrane.
'to sum up'
The researchers designed and synthesized polymer PM7 based on a new chlorine-containing BDT-2Cl donor unit and used it as a donor in non-fullerene organic solar cells. Unlike the chlorinated polymers of the substituents, PM7 is chlorinated on the polymer conjugated side chain, which helps to reduce the steric hindrance effect of Cl atoms on the polymer backbone. Compared with PBDB-T, PM7 has lower The HOMO level, the higher absorption coefficient, the stronger crystallinity and the higher carrier mobility. In addition, the photovoltaic device based on PM7:IT-4F toluene as the solvent was obtained Voc 0. 88V, Jsc is 20. In the case of 9mA·cm− 2 and FF of 71.1%, the PCE was as high as 13.1%, while the PSC based on PBDB-T:IT-4F only obtained 5. 3% of the PCE. 13.1%. PCE is one of the highest values of the non-halogen solvent photovoltaic devices reported so far. The results show that chlorine is a simple, cheap, and effective strategy for designing high performance polymer photovoltaic materials.
