Chloride Substituted Organic Small Molecules For Solar Cell Acceptor Materials: Design,synthesis And Photovoltaic Properties

With the increasing human′s desire for clean renewable energy,how to effectively use solar energy has become an urgent problem for human beings.The complex manufacturing process and high cost of the traditional silicon-based solar cells have prompted scientists to find a more economical and more versatile alternative.In recent decades,organic solar cells have gradually entered the vision field of scientists.Organic solar cells are characterized by low cost,light weight,solvent processing,easy fabrication of flexible devices and translucent devices,and can be widely used in emerging fields such as energy-efficient building integration and wearable devices.The active layer materials of organic solar cells are divided into donor materials and acceptor materials,and non-fullerene small molecule acceptor materials have become a hot spot in organic solar cell research due to a series of advantages such as energy level and absorption spectrum adjustment through structural design.In this paper,the advantages of chlorine atoms in small molecule acceptor materials were combined with the electron-rich core unit containing carbon-oxygen bridges to synthesize a series of A-D-A-type acceptor materials with absorption spectra in the near-infrared region.Then we studied their thermodynamics stability,photoelectric and photovoltaic properties.The main content of this article is divided into the following two parts:（1）The chlorine-substituted eight-membered ring acceptor materials COi8-2Cl-m and COi8-4Cl were synthesized.The research indicated that COi8-4Cl was difficult to dissolve in general organic solvents due to its strong aggregation,so we only studied the photovoltaic performance of COi8-2Cl-m.The PTB7-Th:COi8-2Cl-m device was fabricated with the polymer PTB7-Th,which is complementary to the energy level and absorption spectrum of COi8-2Cl-m,then the energy conversion efficiency（PCE）of 8.42%was obtained.In order to further improve its photovoltaic performance,PC₇₁BM,which is complementary to the energy level and spectrum of this system,was selected as the third element.The PTB7-Th:COi8-2Cl-m:PC₇₁BM devices were fabricated.And the experimental data showed that the optimized device got the best performance,when the active layer ratio PTB7-Th:COi8-2Cl-m:PC₇₁BM=1:1.05:0.45.As a result,the optimized device exhibited a V_oc of 0.73 V,a J_sc of 21.68 mA cm^-2 and a PCE of 9.02%.This study shows that PC₇₁BM can effectively improve the film morphology of the system and form a suitable phase separation scale,which is conducive to the improvement of its photovoltaic performance.（2）The chlorine-substituted six-membered ring acceptor materials COi6-2Cl-γ,COi6-2Cl-δ,COi6-2Cl-m and COi6-4Cl were synthesized.Four materials were separately blended with PTB7-Th to fabricate devices,and the best PTB7-Th:COi6-2Cl-m device had a PCE value of9.22%.In order to study the reasons for the superior photovoltaic performance of the structural uncertain material,we used different proportions of COi6-2Cl-γ,COi6-2Cl-δand PTB7-Th to fabricate five ternary cells.It was found that different ratios have a significant effect on the electron mobility of ternary cells.The device with PTB7-Th:COi6-2Cl-γ:COi6-2Cl-δ=1:0.5:0.5 has the highest electron mobility(μ_e=1.1×10^-4 cm² V^-1 S^-1),and the highest PCE（9.33%）.Studies have shown that mixed materials in this system are more likely to form suitable phase separation scales resulting in higher FF and electron mobility in their devices.However,the determination of the position of the chlorine atom in the end group has little effect on the fused ring system containing the C-O bridge,which indicates that the mixed isomer is also a good strategy to improve the photovoltaic performance of the related system.