Transient Absorption Studies of Bimolecular Recombination Dynamics in Polythiophene/Fullerene Blend Films
Transient Absorption Studies of Bimolecular Recombination Dynamics in Polythiophene/Fullerene Blend Films
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DOI：
10.1021/jp909442s
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发表时间：
2009-12-10
影响因子：
3.7
通讯作者：
Durrant, James R.
中科院分区：
文献类型：
--
作者：
Clarke, Tracey M.;Jamieson, Fiona C.;Durrant, James R.
双分子复合是有机太阳能电池中的一种重要损耗机制，已使用瞬态吸收光谱对聚（3-己基噻吩）:[6,6]-苯基 C-61-丁酸甲酯 (P3HT:PCBM) 薄膜和这些组件的类似物进行了研究。数据根据共混物成分、沉积后热退火和激发密度进行分析。将 P3HT:PCBM 薄膜的瞬态光谱与采用 P3HS 和 PC70BM 的类似薄膜进行比较，可以确定光致吸收特征。这些衰变动力学在纳秒到毫秒的时间尺度上进行了分析，结果表明，在局域（陷阱）态呈指数分布的情况下，这些衰变动力学与双分子重组模型非常一致。热退火导致这些衰变动力学加速，这归因于陷阱态深度的减少并与薄膜结晶度的增加相关。分析衰变动力学以获得有效的复合系数，该系数在低极化子密度下依赖于电荷密度，但在高载流子密度（> 10(18) cm(-3)）下变得与电荷密度无关。这种转变被分配给陷阱填充，在高电荷密度（k = 3 < 10(-12) cm(3) s(-1)）下测量的复合系数对应于无陷阱极限。根据瞬态光谱行为，我们估计未退火的 P3HT:PCBM 共混薄膜中的带内陷阱态密度类似于 7 x 10(17) cm(-3)。
Bimolecular recombination, an important loss mechanism in organic solar cells, has been investigated using transient absorption spectroscopy for poly(3-hexylthiophene):[6,6]-phenyl C-61-butyric acid methyl ester (P3HT:PCBM) films and analogues of these components. Data are analyzed as a function of blend composition, postdeposition thermal annealing, and excitation density. Comparison of transient spectra for P3HT:PCBM films with analogous films employing P3HS and PC70BM allows the assignment of the photoinduced absorption features. These decay dynamics are analyzed oil the nanosecond to millisecond time scales and are shown to be in excellent agreement with a bimolecular recombination model in the presence of an exponential distribution of localized (trap) states. Thermal annealing results in an acceleration of these decay dynamics, which is assigned to a reduction in the depth of the trap states and correlated with an increase in film crystallinity. The decay dynamics are analyzed to obtain an effective recombination coefficient that is charge density dependent at low polaron densities, but becomes independent of charge density at high charge carrier densities (> 10(18) cm(-3)). This transition is assigned to trap filling, with the recombination coefficient measured at high charge density (k = 3 < 10(-12) cm(3) s(-1)) corresponding to the trap-free limit. From transient spectroscopic behavior we estimate the density of intraband trap states in unannealed P3HT:PCBM blend films to be similar to 7 x 10(17) cm(-3).