对poly(3-hexylthiophene) (P3HT)光伏器件产生正、负向磁场效应的原因进行了研究.制作了不同活性层厚度的光伏器件,光电流的磁场效应对厚度的依赖非常明显:在活性层厚度为44 nm时,有2.8％的正效应;当活性层厚度提高为105 nm时,磁场效应变为负值(-5.2％).为了研究产生这种效应的原因,制备了1-(3-methyloxycarbonyl) propyl-1-phenyl[6,6] C61(PCBM)与P3HT共混的器件.在共混器件中,磁场效应随着PCBM比例的提升而逐渐下降直至湮灭且磁场效应不再随活性层厚度发生变化.磁场效应的产生源于磁场可以调控单线态和三线态激子的比例,进而调节单线态激子主导的激子分离作用和三线态激子主导的激子电荷分离作用.实验结果显示出在纯P3HT光伏器件中,当PCBM加入到活性层中时,大量激子在给受体界面处分离成为自由载流子,单线态和三线态激子都可以高效地通过激子分离使光电流增强,激子比例不再影响光电流大小,所以磁场效应逐渐消失且对活性层厚度失去依赖.
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