Improving the Reproducibility of P3HT:PCBM Solar Cells by Controlling the PCBM/Cathode Interface

被引:142
作者
de Villers, Bertrand Tremolet [1 ]
Tassone, Christopher J. [1 ]
Tolbert, Sarah H. [1 ]
Schwartz, Benjamin J. [1 ]
机构
[1] Univ Calif Los Angeles, Dept Chem & Biochem, Los Angeles, CA 90095 USA
基金
美国国家科学基金会;
关键词
IMPEDANCE SPECTROSCOPY; CHARGE-TRANSPORT; POLYMER; MORPHOLOGY; EFFICIENCY; POLY(3-HEXYLTHIOPHENE); BLENDS; ORGANIZATION; MOBILITY;
D O I
10.1021/jp9082163
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Plastic photovoltaic devices offer a real potential for making solar energy economically viable. Unfortunately, bulk heterojunction (BHJ) solai cells fabricated from blends of the commonly used materials poly(3-hexylthiophene), P3HT, and phenyl-C-61-butyric acid methyl ester, PCBM, sometimes exhibit low efficiencies even when the procedures followed often produce solar cells with efficiencies exceeding 5%. In this Letter, we show that this irreproducibility is caused by subtleties in the film processing conditions that ultimately lead to poor electron extraction from the devices. For low-performing devices, photogeneration and charge extraction with a linearly increasing voltage ramp (photo-CELIV) measurements show an order-of-magnitude difference in the effective mobilities of the electrons and holes. Atomic force microscopy (AFM) experiments reveal that the top surface of these low-performing devices is nearly pure P3HT We argue that small variations in the solvent evaporation kinetics during spin-coating of the BHJ active layer, which are difficult to control, cause PCBM to segregate toward the bottom of the P3HT film to different extents, explaining why electron extraction from the PCBM component of the BHJ is so difficult in poorly performing devices. Finally, we show that electron extraction can be greatly improved by spin-coating a thin PCBM layer on top of the BHJ before deposition of the cathode, allowing the reproducible fabrication of high-efficiency polymer solar cells.
引用
收藏
页码:18978 / 18982
页数:5
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