Effects Of Solvent Additives On The Performance Of Polymer Solar Cells

This thesis mainly explored the effect of additives on the photovoltaic performance of BHJ polymer solar cells. We made a concrete analysis from different additives and different volume ratios of the same additive on the performance of polymer solar cells. At last, we were acknowledged with the specific function and mechanism of the additives on the BHJ polymer solar cells.In this work, the effect of solvent additives on the performance of bulk heterojunction (BHJ) polymer solar cells is investigated. The addition of a few percent of solvent additives can give rise to the preferable morphology with well-ordered interpenetrating networks, which is beneficial to charge transport. The enhanced efficiency of polymer solar cells with solvent additives originates from the decreased defects and suppressed trap-assisted recombination at the interface between the donor and acceptor materials. The thesis includes three parts. First,3%volume ratio of BrAni or CN is added into the solvent of the blend film based on P3HT:ICBA in order to study the effect of different additives on the performance of the P3HT:ICBA solar cells. Second, DIO at different volume ratio (1.5%、3%、4.5%) is added into the solvent of the blends based on PCDTBT:PCBM in order to study the effect of different volume ratios of DIO on the photovoltaic performance of the PCDTBT:PCBM solar cells. Third, in order to illustrate the effect of solvent additives on the photovoltaic performance of the devices or the blend films, we use several measurements such as the Ultraviolet-visible (UV-vis) absorption spectrophotometer, the External Quantum Efficiency (EQE), the Morphology (AFM), the Ideality factor (nid), and the Transient photocurrent (TPC). The conclusions of our work are as follows:(1) For P3HT:ICBA BHJ polymer solar cells,3%volume ratio of BrAni or CN is added into the solvent of the blends. With the addition of3%BrAni or CN, the photovoltaic performance of the devices increased by more than10%and30%, respectively.(2) For PCDTBT:PCBM BHJ polymer solar cells,1.5%、3%、4.5%volume ratio of DIO are added into the solvent of the blends. Through the J-V characteristic curves, we found that the photovoltaic performance of the device with1.5%volume ratio of DIO was slightly improved. With3%volume ratio of DIO, the photovoltaic performance of the device achieved the best value, while with4.5%volume ratio of DIO, the photovoltaic performance of the device showed the worst performance.(3) Through the studies on UV-vis absorption, the morphology, the EQE values, the nid, and the TPC of the devices, we found that the enhanced performance of the devices with solvent additives is attributed to the improved morphology of active layers with fewer defects at the donor/acceptor interface, which reduces the trap-assisted recombination of the devices.