Device Structure And Photovoltaic Performance Of Polymer Solar Cells

Polymer solar cells have attracted significant attention due to their predominant advantages of light-weight, low-cost, and many other nice features. In recent years, the conversion efficiency of related polymer solar cell devices have gone beyond 10%, whereas still could not meet the requirements for commercialization. How to design the conjugated polymer and the fabrication technique of solar cells devices have become the focus of researchers. This paper select several typical polymer photovoltaic materials which synthesized in our laboratory to prepare the solar cells devices and investigated the relationship among molecular structure, device fabrication technology and photovoltaic properties. The main research contents and results are as follows:1 We designed and synthesized three conjugated coporymers based on alkylthienyl substituted quinoxaline acceptor unit with different numbers of F substhuents and thiophene donor unit. We found that the introduction of the fluorine substituents results in gradual decrease in the HOMO levels and slightly blue-shift of the absorption, but almost no influence on the LUMO energy levels of the relative polymers. The PSCs based on the synthesized polymers demonstrate gradually increasing PCEs with the increase of F substituents, which were ascribed to the enhanced Voc and Jsc. The introduction of fluorine atoms could induce polymer re-orientation and make the blending film forming interpenetrating network structure. The solar cells devices based on different levels of fluorination show PCEs of 2.82%,4.14% and 5.19% respectively.2 The photovoltaic performance of two D-A conjugated copolymers based on BDT-QX were investigated, their differences are mainly in side chain of BDT. This chapter mainly describe different optimization technology in device fabrication process include thermal annealing, additives, methanol treatment and modified layer treatment. After various optimization methods, the photovoltaic performance of corresponding solar cells devices are improved which ascribe to the different changes of Jsc,Voc and FF. In summary, the obtained optimal PCEs of the two copolymers are 7.88% and 8.51%, the results indicate that the optimization technology have significant effect on photovoltaic performance.3 We have synthesized four different coporymers based on BT-DPP and mainly discuss the role of end-capping to the photovoltaic performance of these coporymers. For this kind of BT-DPP coporymers, we used different end-capping methods respectively, thiophene, quinoxaline porphyrin(QP) and quinoxaline porphyrinatozmc(QPZn) were selected as three end-capping molecule. We compared the photovoltaic performance of the copolymers by device fabrication and characterization in detail. Simultaneously we found that the end-capping could eliminate defects of molecular end group, furthermore QP or QPZn could enhance the shortwave light absorption intensity of copolymers. We also used the annealing treatment, DIO additive and 4,4’-bipyridine (Bipy) additive to optimize the photovoltaic performance and investigated the effect om morphology of blend films. Especially, ligand addivie Bipy, was applied to the PSCs based on polymers end-capped by quinoxaline porphyrinatozinc and the PCE of the photovoltaic device based on P(BT-DPP)-QPZn significantly improved. Finally, the devices efficiency of polymer solar cells based on different end-capping means are 1.48%,2.45% 3.95% and 4.45%, the retention of PCE after device aging improved from 61% to 76% under the action of Bipy.