New progress in hole transport materials for perovskite batteries

The efficiency of hole generation and collection in perovskite solar cells is an important factor that determines the energy conversion efficiency of the cells. Small molecule hole transport materials have very good application potential in perovskite solar cells. Currently, high-efficiency perovskite solar cells mostly use organic small molecule spiro-OMeTAD as the hole-transporting material. However, the synthesis steps are complicated, the cost is high, and the stability in air is poor. Therefore, the development of organic hole transport materials with low cost, easy preparation, high efficiency and high stability is an important research direction of perovskite solar cells.

Recently, with the support of the pilot project of the Chinese Academy of Sciences and the National Natural Science Foundation of China, Zhong Yuwu, a researcher in the Key Laboratory of Photochemistry at the Institute of Chemistry, Chinese Academy of Sciences, and Hu Jinsong, a researcher in the Key Laboratory of Molecular Nanostructures and Nanotechnology, developed a class of low-cost, It is easy to prepare two-dimensional conjugated organic small molecule hole transport material OMe-*** yr and apply it to perovskite solar cells to achieve an average energy conversion efficiency of 20%.

Researchers prepare OMe-*** yr at a total yield of 26% and a gram scale through a four-step simple organic conversion. At this stage, the laboratory cost is about US $ 50 / g, which is more than half the cost of spiro-OMeTAD. Further optimize the synthesis steps and reduce costs. OMe-*** yr has good solubility in common organic solvents and has good film-forming properties. The thermal stability test shows that the compound OMe-*** yr has good thermal stability and is suitable for the preparation of highly stable photovoltaic devices. Electrochemical and spectroscopic studies have shown that the energy level of this hole transport material matches the energy level of ternary perovskite Cs0.05FA0.81MA0.14PbI2.55Br0.45 (CsMAFA). The introduction of the thiophene group in the compound OMe-*** yr enhances the molecular delocalization range of the molecule, stabilizes the HOMO energy level, and is more conducive to hole injection. In addition, due to the certain Pb-S interaction between the S atom in OMe-*** yr and the Pb in perovskite, surface defects in the perovskite crystals can be passivated. The introduction of thiophene groups can improve the carrier transport capability and inhibit interface recombination, improve device efficiency and weaken the hysteresis effect. The energy conversion efficiency of perovskite solar cells based on OMe-*** yr can reach 20.6%, and the average energy conversion efficiency is 20.0%. The unpackaged device maintained an initial efficiency of 92% after being placed for 60 days. The compound OMe-*** yr is one of the few reported hole-transporting organic small molecules with an energy conversion efficiency of more than 20%, and has good application prospects. Related work was recently published on Angew. Chem. Int. Ed. 2018, 57, 10959, and was highlighted by Sci. China Chem. (DOI: 10.1007 / s11426-018-9331-y). Relevant achievements have applied for Chinese patents (patent application number .0).

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