The organic solar cell is composed of a p-type organic semiconductor (p-OS) donor and an n-type organic semiconductor (n-OS) acceptor blended active layer sandwiched between a transparent conductive electrode and a metal electrode. The advantages of light weight, low cost and flexible and translucent devices that can be prepared by solution processing methods have become research hotspots in the field of new energy research in recent years. The p-OS donor photovoltaic materials include conjugated polymers and small organic molecules. Compared with polymers, small-molecule materials have the advantages of definite molecular structure, no difference in synthetic batches, and easy purification. Therefore, organic small-molecule donor photovoltaic materials have also attracted widespread attention. All-small molecule non-fullerene organic solar cells use p-OS small molecule donors and n-OS small molecule acceptors, and have the advantages of small molecule donor materials and non-fullerene small molecule acceptor materials, and have recently become organic An important research direction in the field of solar cells.
With the support of the pilot project of the Chinese Academy of Sciences, the research team of Li Yongfang, a key laboratory of organic solids, Institute of Chemistry, Chinese Academy of Sciences, recently obtained a series of studies in the research of p-OS small molecule donor materials and all small molecule non-fullerene organic solar cells Progress has enabled the energy conversion efficiency of all small molecule organic solar cells to exceed 10%.
The p-OS small molecule donor material mostly adopts A-Ï€-D-Ï€-A type (where D represents the donor structural unit and A represents the acceptor structural unit) linear molecular structure. On the basis of the J-series high-efficiency polymer donor photovoltaic materials they developed for non-fullerene polymer solar cells, they J-series polymers were made into small molecules and synthesized based on benzodithiophene (BDT ) Is the donor unit, the fluorine-substituted triazole (FBTA) is the acceptor unit, and the acetonitrile ester group is the terminal acceptor unit p-OS small molecules H11 and H12 (see Figure 1 for the molecular structure). The open circuit voltage (Voc) of all small molecule organic solar cells with H11 as the donor and n-OS small molecule IDIC as the acceptor reaches 0.977V, and the energy conversion efficiency (hereinafter referred to as efficiency) reaches 9.73% (J.Am.Chem.Soc .2017,139,5085-5094.).
The n-OS small molecule acceptor material has the characteristics of an anisotropic conjugated skeleton, so the molecular structure of p-OS is optimized to adjust the morphology of the entire small molecule active layer to form a good donor-acceptor nanoscale phase separation The interpenetrating network structure is an important means to improve the photovoltaic performance of all small molecule organic solar cells. Using BDT as the central donor unit, they introduced the oligothiophene structure into the p-OS molecular structure and synthesized two p-OS molecules SM1 and SM2 (see Figure 1 for the molecular structure). The efficiency of all small molecule organic solar cells based on SM1: IDIC reaches 10.11% (Chem Mater. 2017,29,7543–7553.), Which is the first time that the efficiency of all small molecule non-fullerene organic solar cells has exceeded 10%.
In two-dimensional conjugated polymers based on thiophene-substituted BDT, the silane-based side chain can effectively reduce the HOMO energy level of the polymer, enhance absorption and increase hole mobility. In order to further improve the photovoltaic performance of all small-molecule organic solar cells, they recently introduced a two-dimensional BDT unit with silanethiophene as the side chain into the p-OS small molecule donor material, and synthesized two new p-OS small molecules. Molecular donor photovoltaic materials H21 and H22 (the molecular structure is shown in Figure 1), and the effects of different terminal acceptor units on the physical and chemical properties of the material and its photovoltaic performance were studied. The photoelectric conversion efficiency of all small molecule organic solar cells based on H22: IDIC was further improved to 10.29%. This result was recently published in "Advanced Materials" (Adv. Mater., 2018, 30, 1706361.).
Figure: Molecular structure of p-OS small molecule donor and n-OS small molecule acceptor IDIC, device structure of all small molecule organic solar cells, and energy conversion efficiency of all small molecule organic solar cells based on each donor material
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