Wideband Gap Solar Cell Materials and Their Laminated Devices

Polymer solar cells have the unique advantages of light weight, flexibility, and low cost. They have received extensive attention from scientists around the world in the past 10 years. How to maintain the high open circuit voltage is an important research area in the field of organic photovoltaics while broadening the absorption of molecular materials. The use of a stacked device structure to connect two single-junction cells having different absorption ranges in series can achieve wide absorption spectrum and high open-circuit voltage at the same time, which is one of the effective methods for improving the efficiency of organic solar cells. At present, there are relatively few types of wide bandgap polymeric photovoltaic materials, which to a certain extent limit the spectral complementarity between the subcells of a laminate battery, thereby further limiting the efficiency.

Under the support of the National Outstanding Young Scientists Fund project and the China National Academy of Strategic Pilot Science and Technology project, the Zheng Qingdong Research Group of the State Key Laboratory of Structural Chemistry of the Fujian Institute for the Study of Structures of the Chinese Academy of Sciences and the Ma Wei team of Xi’an Jiaotong University have designed and synthesized these conditions and problems. A class of D--A wide bandgap polymeric materials containing a trapezoidal fused ring that leads to the merging dithiophene units. The material realizes the optimization of the energy level, bandgap, molecular chain conformation and carrier transport performance of the polymer, and finally improves the photoelectric conversion efficiency of the battery device. Based on the optimized polymer, a single junction solar cell having a photoelectric conversion efficiency of 8.15% was prepared. Further, they used this type of wide bandgap polymer and benzodithiophene narrow band gap polymer (PTB7-Th) as donor materials for the front and rear batteries, respectively, and successfully prepared a new binary mixed interface layer. The tandem solar cell has a device conversion efficiency of 11.15% and an open circuit voltage of 1.70V. The results were recently published online in Nano Energy (2017, 33, 313-324). This work not only provides a new idea for the design synthesis of highly efficient wide bandgap polymer materials, but also provides a new choice for the interfacial layer in tandem solar cells.

Previously, the team used asymmetric pyrenethiophene as a building block for the design and synthesis of new wide band gap polymer solar cell materials (Adv. Mater. 2016, 28, 3359-3365, Adv. Electron. Mater., 2016, 2, 1600340), successfully prepared a solar cell device with an open circuit voltage of up to 1.0V and a conversion efficiency of 9.0% or more. In addition, the team was invited to write a review paper titled Recent advances in wide bandgap semiconducting polymers for polymer solar cells (J. Mater. Chem. A, 2017, 5, 1860-1872).

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