Chemical Engineering Department and Frontier Research Center on Fundamental and Applied Sciences of Matters, National Tsing-Hua University, Hsinchu 30013, Taiwan, ROC.
J Am Chem Soc. 2012 Sep 5;134(35):14271-4. doi: 10.1021/ja303813s. Epub 2012 Aug 24.
We present a novel electron transport (ET) polymer composed of polyfluorene grafted with a K(+)-intercalated crown ether involving six oxygen atoms (PFCn6:K(+)) for bulk-heterojunction polymer solar cells (PSCs) with regioregular poly(3-hexylthiophene) (P3HT) as the donor and indene-C(60) bisadduct (ICBA) or indene-[6,6]-phenyl-C(61)-butyric acid methyl ester (IPCBM) as the acceptor in the active layer and with Al or Ca/Al as the cathode. A remarkable improvement in the power conversion efficiency (PCE) (measured in air) was observed upon insertion of this ET layer, which increased the PCE from 5.78 to 7.5% for a PSC with ICBA and Ca/Al (5.53 to 6.63% with IPCBM) and from 3.87 to 6.88% for a PSC with ICBA and Al (3.06 to 6.21% with IPCBM). This ET layer provides multiple functionalities: (1) it generates an optical interference effect for redistribution of light intensity as an optical spacer; (2) it blocks electron-hole recombination at the interface with the cathode; (3) it forms an interfacial dipole that promotes the vacuum level of the cathode metal; and (4) it enhances electron conduction, as evidenced by (1) the increase in total absorption of 1:1 w/w P3HT:ICBA by a factor of 1.3; (2) the reduction in the hole-only current density profile by a factor of 3.3 at 2.0 × 10(5) V/cm; (3) the decrease of 0.81 eV in the work function of Al from 4.28 to 3.47 eV, as determined by UV photoelectron spectroscopy; and (4) the decrease in the series resistance of PSCs with ICBA and Al by a factor of 4.5, as determined by the current-voltage characteristic under dark conditions; respectively. The PSC of 7.5% is the highest among the reported values for PSC systems with the simplest donor polymer, P3HT.
我们提出了一种新型的电子传输（ET）聚合物，由聚芴接枝具有 K(+)嵌入的六氧原子冠醚组成（PFCn6:K(+)），用于本体异质结聚合物太阳能电池（PSCs），其中给体为具有规正结构的聚（3-己基噻吩）（P3HT），受体为茚并[C60]二加成物（ICBA）或茚并[6,6]-苯基-C61-丁酸甲酯（IPCBM），在活性层中采用 Al 或 Ca/Al 作为阴极。在插入这个 ET 层后，我们观察到功率转换效率（在空气中测量）显著提高，对于采用 ICBA 和 Ca/Al 的 PSC，其效率从 5.78%提高到 7.5%（采用 IPCBM 时为 5.53%至 6.63%），对于采用 ICBA 和 Al 的 PSC，其效率从 3.87%提高到 6.88%（采用 IPCBM 时为 3.06%至 6.21%）。这个 ET 层提供了多种功能：（1）它作为光学间隔物产生光学干涉效应，重新分配光强度；（2）它阻止在与阴极的界面处电子-空穴复合；（3）它形成界面偶极子，促进阴极金属的真空能级；（4）它增强电子传导，这一点可以通过以下几点得到证明：（1）1:1 w/w P3HT:ICBA 的总吸收增加了 1.3 倍；（2）空穴电流密度分布减少了 3.3 倍，在 2.0×10(5) V/cm 时；（3）通过紫外光电子能谱测定，Al 的功函数从 4.28 降低到 3.47 eV，降低了 0.81 eV；（4）在黑暗条件下通过电流-电压特性测量，ICBA 和 Al 的 PSC 的串联电阻降低了 4.5 倍。7.5%的 PSC 是具有最简单给体聚合物 P3HT 的 PSC 系统的最高报道值之一。
