Research Team from Suzhou University: Dialkyl sulfide chain can be applied in high-efficiency polymer solar cells in the future

 When it comes to solar cells, you must be familiar with the terms monocrystalline silicon, gallium arsenide, perovskite, etc. So is there a place for polymers in the field of solar power generation?

Polymer semiconductor materials are the cheapest and most promising solar cell materials. Its advantages are as follows: 1 The synthesis cost is low, and the material selection range is wide. 2 The preparation process is simple, and large-scale mass production can be achieved by simple evaporation, solution method, roller printing, etc. 3 The function and structure are easy to modulate, and the functional group of the organic material can be processed by a simple chemical reaction. 4 Flexibility and film formation are good, and there is a promising field in the field of flexibility and wearability. Since the advantages of polymer solar cells are so great, the research on polymer solar cells has become a hot topic in recent years.

The absorption spectrum of the donor material, the HOMO level, and the morphology after blending with the acceptor material are key factors in determining the energy conversion efficiency of the polymer solar cell. The electron-side chain alkane chain has π electron-withdrawing properties due to the empty d-orbital of the sulfur atom. Associate Professor Cui Chaohua of the Academician Li Yongzhen of Suzhou University introduced the alkylthio chain into the BDT unit, and the unique characteristics of the alkyl sulfide chain could effectively reduce the HOMO level of the donor material, increase the open circuit voltage of the device, thereby increasing the energy conversion efficiency (Energy Environ. Sci., 2014, 7, 2276–2284; Adv. Mater., 2015, 27, 7469–7475; Energy Environ. Sci , 2016, 9, 885–891); in addition, they first reported polymer donor materials based on the electron-withdrawing unit naphtho[2,3-c]thiophene-4,9-dione (NTDO) in 2011. A 5.21% device energy conversion efficiency (PCE) embodies the potential of NTDO cells for efficient donor photovoltaic design (Chem. Commun., 2011, 47, 11345–11347).

Based on the previous series of work, recently, they introduced an alkyl sulfide chain into the NTDO unit, and designed and synthesized a bis-thiol-substituted conjugated polymer PBN-S as a donor material for the polymer solar cells, which have achieved excellent photovoltaic performance. PBN-S has an absorption spectrum complementary to the non-fullerene receptor IT-4F and a lower HOMO level. The polymer solar cell device was prepared by using PBN-S as the donor and IT-4F as the acceptor, and the PCE reached 13.10%. At the same time, the translucent device PCE based on PBN-S:IT-4F also reached 9.83%, and the average transmittance in the visible region (370-740 nm) was as high as 32%. Not only that, PBN-S also achieved outstanding photovoltaic performance on large-area devices: 100 mm² device prepared by spin coating method, PCE was 10.21%; 100 mm² device prepared by blade coating method, PCE was as high as 10.69% . Moreover, the PBN-S:IT-4F-based device has good stability, and the device can be placed in a glove box or air (without protection from light) for 100 days, and the efficiency can maintain more than 80% of the original efficiency.

The results show that the polymer donor material PBN-S based on dialkyl sulfide chain instead of NTDO has great potential in the practical application of high-efficiency polymer solar cells in the future.

Edited by Suzhou Yacoo Science Co., Ltd.