Research group of Professor Peng Qiang of Sichuan University: a new breakthrough in the photoelectric conversion efficiency of P3HT polymer solar cells through simple solution processing

At present, P3HT is one of the most easily industrialized polymer materials in the field of organic solar cells However, the photoelectric conversion efficiency of organic solar cells based on P3HT is far behind that of the most efficient organic solar cells In addition, the preparation process of P3HT device often depends on halogenated solvent, halogenated additives and thermal annealing process to optimize its morphology, which is not conducive to the practical application in the future So how to improve the performance of P3HT device is a challenging problem Recently, Professor Peng Qiang's research group of Sichuan University has made a new breakthrough in this field (adv mater., 2019, DOI: 10.1002/adma.201906045) Prof Peng Qiang, Professor of School of chemistry, Sichuan University, fixed member of National Key Laboratory of polymer materials engineering, doctoral supervisor He has successively won the national outstanding youth fund, the Ministry of education's outstanding talents in the new century, the Sichuan thousand talents program, the academic and technical leaders of Sichuan Province, and the Sichuan outstanding youth fund It is mainly engaged in the molecular design and synthesis of organic small molecules and polymer solar cell key materials (donor, acceptor, interface materials) and the research and development of new process of organic solar cell devices In recent years, more than 1400 academic papers have been published in energy energy SCI., adv mater., J am Chem SOC., adv energy mater., adv funct Mater., nano energy, ACS Nano and other domestic and foreign journals, more than 120 papers have been included in SCI, 32 of which have impact factors greater than 10.0, and more than 400 times have been cited by others He has written 2 chapters of academic monograph, applied for 18 Chinese invention patents (10 have been authorized), and won 1 provincial and ministerial Natural Science Award (ranking 1) Cutting edge scientific research achievements: simple solution processing to achieve the photoelectric conversion efficiency of P3HT polymer solar cells new breakthrough organic solar cells have many outstanding advantages, such as low cost, light weight, large-scale solution preparation into flexible devices, etc., which are widely concerned by academia and industry In recent years, the rise of non fullerene derivatives as receptor materials has overcome the shortcomings of traditional fullerene preparation, such as high cost, weak absorption in visible light region, energy level is not easy to control and so on However, there are still many challenges for the industrialization of organic solar cells: (1) the synthesis of high-efficiency donor acceptor materials is generally complex and the production capacity is not high; (2) there are serious batch differences in polymer donor materials; (3) the preparation of materials often involves the use of high toxic intermediates (such as organotin intermediates) that are harmful to the environment（ 4) In the process of device preparation, halogenated solvents (such as chlorobenzene, chloroform, etc.) and additives (such as chloronaphthalene, 1,8-diiodoctane, etc.) which are harmful to human body and ecological environment are often used; (5) post-treatment processes (such as thermal annealing, solvent evaporation and annealing, etc.) are often used for device optimization, increasing process complexity and production cost At present, poly (triahexylthiophene) (P3HT) is one of the most easily mass-produced polymer materials with low cost and controllable batch difference Therefore, P3HT is very suitable for commercial production of polymer donor materials However, the photoelectric conversion efficiency of polymer solar cells based on P3HT is far behind the most efficient polymer organic solar cells Secondly, the preparation of P3HT devices often depends on halogenated solvents, halogenated additives and thermal annealing process to control their morphology, which is not conducive to industrial production In order to solve the above problems, we have synthesized a new small molecule receptor trbtic, which can form a better absorption complementary and energy level matching with P3HT The small molecule is based on tripolyindene (TR uxene), and the benzothiadiazole cyanidinone electrodeficient group is used as the terminal group (as shown in Fig 1a) Fig 1 (a) chemical structure of P3HT and trbtic; (b) P 3ht: schematic diagram of trbtic aggregation changing with solution aging time; (c) UV-Vis absorption spectrum of trbtic in TMB; (d) UV-Vis absorption spectrum of P3HT and trbtic films prepared at different solution aging time; UV-Vis absorption spectrum of P3HT and trbtic blend films prepared at different solution aging time (source: adv mater.) Fig 2 Time dependent diagram of 1,2,4-trimethylbenzene solution of P3HT at room temperature (source: adv mater.) in the process of device preparation, the author found that P 3ht can be used in 1,2 of heat (60oC), 4 - trimethylene (TMB) is well dissolved, but P3HT accumulates slowly at room temperature (Fig 2) Based on this property, the pre aggregation of P 3ht: trbtic in solution was controlled by adjusting the aging time of solvent at room temperature (Fig 1b) When the solvent aged for 40 minutes, the photoelectric conversion efficiency increased significantly from 6.62% to 8.25%, becoming the latest world record of photoelectric conversion efficiency of organic solar cells based on P3HT (Figure 3) Figure 3 P3HT prepared by different solvent aging time: trbtic device's (a) current density voltage curve and (b) external quantum efficiency curve; (c) photoelectric conversion efficiency open circuit voltage relationship comparison of polymer solar cell based on P3HT; (d) short circuit current density open circuit voltage relationship comparison of polymer solar cell based on P3HT (source: adv Mater.) in order to study the effect of solvent aging on the performance of the device, the changes of crystallinity and phase separation of the active layer were measured by wide angle grazing incidence X-ray diffraction (giwaxs) and atomic force microscopy (AFM) As shown in Figure 4, the crystallinity of the active layer increases with the increase of solution aging time After 60 minutes, the polycrystalline diffraction of the active layer was obvious The results show that solvent aging can promote the active layer to pre crystallize in solution and increase the crystallinity of the active layer Fig 4 The giwaxs diagram (source: adv mater.) of receptor pure film and blend film is shown in Fig 5 With the increase of solution aging time, the phase separation of active layer film increases gradually After aging for 40 minutes, the active layer obtained an ideal fibrous phase separation structure, which promoted exciton separation and charge transfer, thus revealing the reason of the optimal photoelectric conversion efficiency With the increase of aging time, the phase separation increases significantly, the interface of donor and acceptor is reduced, the exciton separation is inhibited, and the device efficiency is reduced Fig 5 AFM, A-D, and E-H phase diagrams of P3HT: active layer films prepared by trbtic solution with different aging times Conclusion: a new small molecule receptor material, trbtic, which can form better absorption complementary and energy level matching with P3HT, has been synthesized by molecular design At the same time, the crystallization degree of P3HT in the preparation of active layer can be controlled by simple solvent aging process, so as to optimize the morphology of P3HT: trbtic active layer This strategy has successfully improved the photoelectric conversion efficiency from 6.62% to 8.25%, which is the latest record of the photoelectric conversion efficiency of organic solar cells based on P3HT Using the green solvent 1,2,4 - trimethylene, without any additives and any post-treatment process, the method is simple, efficient and conducive to industrial production It not only significantly improves the photoelectric conversion efficiency of P3HT, but also provides a new solution for the shape control of high-performance non fullerene organic solar cells This work was published under the title of "P3HT based polymer solar cells with 8.25% efficiency enabled by a matched molecular acceptor and smart green solvent processing technology", and the first author of the paper was Xu Xiaopeng, a doctoral graduate of Sichuan University (adv material., 2019, DOI: 10.1002/adma.201906045) The corresponding author is Professor Peng Qiang of Sichuan University and associate researcher Yu Liyang Nowadays, people and scientific research have been paid more and more attention in the economic life China has ushered in the "node of science and technology explosion" Behind the progress of science and technology is the work of countless scientists In the field of chemistry, in the context of the pursuit of innovation driven, international cooperation has been strengthened, the influence of Returned Scholars in the field of R & D has become increasingly prominent, and many excellent research groups have emerged in China For this reason, CBG information adopts the 1 + X reporting mechanism CBG information website, chembeangoapp, chembeango official micro blog, CBG information wechat subscription number and other platforms jointly launch the column of "people and scientific research", approach the representative research groups in China, pay attention to their research, listen to their stories, record their demeanor, and explore their scientific research spirit.