磁场对聚合物光电池中电流的影响

Effects of magnetic field on current in polymer photovoltaic cell

制备了结构为ITO/PEDOT:PSS/P3HT:PCBM/Ca/Al的聚合物光电池器件,并在不同偏压下,分别测量了器件的光电流和暗电流随外加磁场的变化.发现随外加磁场增加,光电流增强,暗电流减弱.从聚合物光电池中光电流和暗电流的产生机制出发,对该现象进行了解释,认为外加磁场可以有效改变单重态极化子对和三重态极化子对之间的相对比例,进而使自由载流子浓度增加.光生自由载流子浓度增加是光生电流增强的原因,而自由载流子与三重态激子的相互作用导致了暗电流减弱.开路电压附近,光电流随磁场增加而增强可以近似认为是以上两个效应的综合.

Polymer photovoltaic cells were fabricated with the basic device structure of ITO/PEDOT： PSS/P3HT： PCBM/Ca/Al. The magnetic-field-dependent current under illumination and in darkness in these devices were measured respectively under different bias. It was found that the light current was enhanced by the magnetic field whereas the dark current was suppressed. Based on the formation mechanism of the light current and the dark current in polymer solar cell, the observed magnetic field effects were explained. The results show that the magnetic field can effectively change the relative ratio between the singlet and the triplet polaron pairs, resulting in an increase in the density of the free carriers. The concentration augmentation of photo-generated free carriers is responsible for the increase of the photocurrent. On the other hand, the interaction between the free carriers and triplet excitons leads to the decrease of the dark current. Around the open circuit voltage, the magnetic field dependent photocurrent and dark current acting together causes the magnetic field effect of light current.