Singh Sanjeev, Vardeny Zeev Valy
Department of Physics & Astronomy, University of Utah, Salt Lake City, UT 84112, USA.
Materials (Basel). 2013 Mar 6;6(3):897-910. doi: 10.3390/ma6030897.
We measured the picoseconds (ps) transient dynamics of photoexcitations in blends of regio-regular poly(3-hexyl-thiophene) (RR-P3HT) (donors-D) and fullerene (PCBM) (acceptor-A) in an unprecedented broad spectral range of 0.25 to 2.5 eV. In D-A blends with maximum domain separation, such as RR-P3HT/PCBM, with (1.2:1) weight ratio having solar cell power conversion efficiency of ~4%, we found that although the intrachain excitons in the polymer domains decay within ~10 ps, no charge polarons are generated at their expense up to ~1 ns. Instead, there is a build-up of charge-transfer (CT) excitons at the D-A interfaces having the same kinetics as the exciton decay. The CT excitons dissociate into separate polarons in the D and A domains at a later time (>1 ns). This "two-step" charge photogeneration process may be typical in organic bulk heterojunction cells. We also report the effect of adding spin 1/2 radicals, Galvinoxyl on the ultrafast photoexcitation dynamics in annealed films of RR-P3HT/PCBM blend. The addition of Galvinoxyl radicals to the blend reduces the geminate recombination rate of photogenerated CT excitons. In addition, the photoexcitation dynamics in a new D-A blend of RR-P3HT/Indene C60 trisadduct (ICTA) has been studied and compared with the dynamics in RR-P3HT/PCBM.
我们在前所未有的0.25至2.5电子伏特宽光谱范围内，测量了区域规整聚（3 - 己基噻吩）（RR - P3HT）（供体 - D）与富勒烯（PCBM）（受体 - A）混合物中光激发的皮秒（ps）瞬态动力学。在具有最大域分离的供体 - 受体混合物中，例如重量比为（1.2:1）且太阳能电池功率转换效率约为4%的RR - P3HT/PCBM，我们发现尽管聚合物域内的链内激子在约10皮秒内衰减，但在长达约1纳秒的时间内，不会以它们为代价产生电荷极化子。相反，在供体 - 受体界面处有电荷转移（CT）激子的积累，其动力学与激子衰减相同。CT激子在稍后的时间（>1纳秒）解离成供体和受体域中的单独极化子。这种“两步”电荷光生过程在有机本体异质结电池中可能是典型的。我们还报告了添加自旋1/2自由基加尔文oxyl对RR - P3HT/PCBM混合物退火薄膜中超快光激发动力学的影响。向混合物中添加加尔文oxyl自由基降低了光生CT激子的双分子复合率。此外，还研究了RR - P3HT/茚C60三加成物（ICTA）的新型供体 - 受体混合物中的光激发动力学，并与RR - P3HT/PCBM中的动力学进行了比较。
