制备了MEH-PPV(poly［2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene］)和PCBM (1-(3-mehyloxycarbonyl)propy1-phenyl［6,6］C61)共混体系的聚合物太阳能电池。 通过改变MEH-PPV∶PCBM(质量比为1∶4)混合溶液的浓度及旋涂时的转速来改变活性层的厚度, 研究了器件性能随活性层厚度的变化。 当旋涂速率小于4 000 r·min-1时随着厚度的减小, 开路电压没有明显的变化, 基本在0.8 V左右, 但短路电流呈现单调上升的趋势, 填充因子略有下降。 当旋涂速率大于5 000 r·min-1时, 开路电压和短路电流都开始下降。 其中, 开路电压从5 000 r·min-1时的0.78 V下降到8 000 r·min-1时的0.67 V, 短路电流更是从5 000 r·min-1时的3.96 mA·cm-2下降到8 000 r·min-1 时的1.76 mA·cm-2。 短路电流受光吸收和载流子传输两方面的共同影响, 而活性层厚度的变化使得这两方面的影响产生相悖的效果。 活性层越厚, 光生激子数越多, 但同时内建电场变弱, 而且激子解离后得到的载流子传输到相应电极的距离越长, 载流子被电极收集的概率减小。 开路电压的降低则源于激子在MEH-PPV和PCBM与相应电极界面处解离比重的增加。

Bulk heterojunction polymer solar cells based on the blend of MEH-PPV (poly［2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene］) and PCBM (1-(3-mehyloxycarbonyl)propy1-phenyl［6,6］C61) were fabricated. The thickness of the active layer was controlled by changing the concentration of MEH-PPV∶PCBM (1∶4 in weight ratio) solution and spin speeds. Investigation of the effects of active layer thicknesses on the performance of the photovoltaic devices indicates that, when the spin-coated speeds are lower than 4 000 r·min-1 (round per minute), the open-circit voltage (Voc) remains almost unchanged at approximately 0.8 V, whereas the short-circuit density (Jsc) monotonically increases and the fill factor (FF) decreases slightly. The spin speeds that are higher than 5 000 r·min-1 rpm result in the Voc and Jsc both reduced. The Voc decreases from 0.78 V at the spin-speed of 5 000 r·min-1 to 0.67 V at 8 000 r·min-1, and the Jsc even decreases from 3.96 mA·cm-2 at 5 000 r·min-1 to 1.76 mA·cm-2 at 8 000 r·min-1. Jsc depends on the mutual impact of light absorption and carrier transport, while a contradicting effect from the two aspects is caused by varying the thickness of the active layer. The thicker the active layer, the more the excitons induced by light absorption. However, the build-in electric field becomes weaker and the pathway becomes longer for transporting the opposite charge carriers derived from exiciton separation to their corresponding electrodes at the same time, which makes the probability of charges collection by respective electrodes lower. With respect to the reduced Voc, it may be attributed to the increased proportion of exciton dissociation at the interfaces of MEH-PPV and PCBM with the relevant electrodes.