Influence of the percolation network geometry on electron transport in dye-sensitized titanium dioxide solar cells
Influence of the percolation network geometry on electron transport in dye-sensitized titanium dioxide solar cells
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DOI：
10.1021/jp022681l
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发表时间：
2003-08-07
影响因子：
3.3
通讯作者：
Frank, AJ
中科院分区：
文献类型：
--
作者：
Benkstein, KD;Kopidakis, N;Frank, AJ
应用逾渗理论研究了网络结构对染料敏化纳米TiO2太阳能电池中电子输运动力学的影响，并与瞬态光电流测量结果进行了比较.膜的孔隙率通过实验从52%变化到71%。电子输运建模使用模拟介孔TiO 2膜，由一个随机的纳米粒子网络，和随机行走的方法。通过网络的电子传输路径与膜的孔隙率和膜中粒子的配位数相关。实验测量和随机行走模拟与逾渗理论定量一致，逾渗理论预测电子扩散系数D对膜孔隙率的幂律依赖性，如关系式所述：D与\P-P-c\（u）成比例。临界孔隙度P-c（逾渗阈值）和电导率指数μ分别为0.76 +/-0.01和0.82 +/-0.05。的纳米颗粒膜的分形维数估计从模拟为2.28，这是在定量协议与气体吸附测量。结果表明，随着孔隙率的增加，粒子的配位数的分布从强调高配位数转移到低的，导致电子传输路径变得更加曲折和电子传输减慢。增加孔隙率的另一个后果是，在TiO 2膜中的终止颗粒（死端）的分数显着增加，从小于1%的50%的多孔膜的31%的75%的多孔膜。据估计，在它们分别通过50%和75%的多孔10 μ m厚的膜的过程中，电子访问的颗粒的平均数量增加了10倍，从10（6）增加到10（7）。这项研究提供了第一个明确的证据表明，网络拓扑结构有很强的影响，在介孔TiO 2薄膜的电子传输动力学。
Percolation theory is applied to understand the influence of network geometry on the electron transport dynamics in dye-sensitized nanocrystalline TiO2 solar cells, and the predicted results are compared with those measured by transient photocurrent. The porosity of the films was varied experimentally from 52 to 71%. Electron transport was modeled using simulated mesoporous TiO2 films, consisting of a random nanoparticle network, and the random-walk approach. The electron transport pathway through the network was correlated with the film porosity and the coordination numbers of the particles in the film. The experimental measurements and random-walk simulations were in quantitative agreement with percolation theory, which predicts a power-law dependence of the electron diffusion coefficient D on the film porosity as described by the relation: D proportional to \P - P-c\(u). The critical porosity P-c (percolation threshold) and the conductivity exponent mu were found to be 0.76 +/- 0.01 and 0.82 +/- 0.05, respectively. The fractal dimension of the nanoparticle films was estimated from the simulations to be 2.28, which is in quantitative agreement with gas-sorption measurements. It is shown that as the porosity increases, the distribution of the coordination numbers of the particles shifts from an emphasis on high coordination numbers to low ones, causing the electron transport pathway to become more tortuous and electron transport to slow. Another consequence of increasing the porosity is that the fraction of terminating particles (dead ends) in the TiO2 film increases markedly, from less than 1% for a 50% porous film to 3 1% for a 75% porous film. It is estimated that during their respective transit through 50 and 75% porous 10-mum thick films, the average number of particles visited by electrons increases by 10-fold, from 10(6) to 10(7). This study provides the first clear evidence that network topology has a strong influence on the electron transport dynamics in mesoporous TiO2 films.