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Conformal-adjustable organic hole transport material for efficient and stable perovskite solar cells

2019-06-04 来源:亚科官网
 
Perovskite solar cells have become a research hotspot in the field of photovoltaics due to their high efficiency, low cost and simple preparation. As an important component of perovskite solar cells, organic hole transport materials can promote the extraction of holes and block electrons, which is of great significance for improving the photoelectric performance of batteries. Hole mobility and film quality are key factors in the application of organic hole transport materials (HTM), but the lack of a design module that effectively regulates the molecular configuration allows for both. Molecules in a planar configuration tend to form ordered molecular packing (easy to crystallize), thereby promoting charge transport between molecules to achieve high mobility. However, in order to obtain a dense and uniform organic film, the molecules need to maintain an amorphous state and avoid crystallization, which requires a large sterically hindered molecular configuration, the most common of which is an orthogonal configuration.
Spiro-OMeTAD is the most common organic hole transport material in perovskite solar cells. The core of its molecular configuration is the orthogonal snail unit, which can achieve high glass transition temperature, thus ensuring film uniformity and stability. However, the interaction between the molecules of Spiro-OMeTAD is weak, so the intrinsic hole mobility is low (10-6-10-5 cm2 V-1s-1). In order to optimize device performance, it is necessary to dope to increase hole mobility, but the hydrophilicity of the additive (lithium salt, cobalt salt, etc.) greatly reduces the stability of the device. Therefore, a new type of dopant-free organic hole transport material is urgently needed.
Based on the current research status and problems, Zhu Weihong of East China University of Science and Technology has innovatively introduced the conformationally adjustable tetrathiophene ethylene (TTE) as the core unit to explore the design strategy of new undoped hole transport materials. The structure of tetrathiophene ethylene is that a pair of trans thiophenes are coplanar with a double bond, and the other pair is almost perpendicular to this plane, similar to the orthogonal configuration of the snail. The cis-thiophene in TTE can regulate the planarity of the molecule by chemically reacting the ring, and a pair of cis-thiophenes is closed to obtain a semi-locked TTE unit. The TTE and the half-locked TTE were used as the core unit, and four p-methoxytriphenylamine groups were bonded to synthesize the hole transport materials TTE-1 and TTE-2. For the special structure of TTE-2, the work first proposed the concept of planar-orthogonal hybrid configuration, achieving a perfect balance of mobility and film morphology.
Based on a formal planar structure of perovskite solar cells, undoped TTE-2 is used as a hole transporting material, and the device efficiency is optimized to obtain a photoelectric conversion efficiency of 20.04%. It is the most excellent efficiency in disposable-free perovskite solar cell. This work was recently published on the Angewandte Chemie International Edition.
The related work was completed by the doctoral student Shen Chao under the joint guidance of Professor Zhu Weihong and Professor Wu Yongzhen, and was guided by Academician Tian He of East China University of Science and Technology. The work has won the research projects of the Fund's innovative research group project, the National Natural Science Foundation of China, the Shanghai Oriental Scholars Talent Program, the Shanghai Natural Science Foundation, the Chinese Chemical Society's “Young Talents Entrustment Project” and the Fundamental Research Funds of the Central Universities. Funding.
Edited by Suzhou Yacoo Science Co., Ltd.