Charge transport versus recombination in dye-sensitized solar cells employing nanocrystalline TiO2 and SnO2 films
Charge transport versus recombination in dye-sensitized solar cells employing nanocrystalline TiO2 and SnO2 films
复制标题
DOI：
10.1021/jp050145y
复制
发表时间：
2005-06-30
影响因子：
3.3
通讯作者：
Durrant, JR
中科院分区：
文献类型：
--
作者：
Green, ANM;Palomares, E;Durrant, JR
我们报告了采用纳米晶 TiO2 和 SnO2 薄膜的染料敏化太阳能电池 (DSSC) 中的电荷传输和复合动力学的比较，并讨论了这些动力学对光伏器件效率的影响。金属氧化物薄膜中电子传输的瞬态光电压研究与氧化敏化剂染料和氧化还原对的电子复合的瞬态吸收研究相关。对于所有三个过程，观察到 SnO2 电极的动力学速度快了 2-3 个数量级。这些更快动力学的起源通过将电子复合动力学与染料阳离子相关联的研究与薄膜电子密度的计时安培研究来解决。这些研究表明，SnO2 电极更快的复合动力学源于在匹配电子密度下高 100 倍的电子扩散常数（与该金属氧化物相对于 TiO2 的较低陷阱密度一致），以及 SnO2 导带/陷阱态密度相对于 TiO2 的 300 mV 正移。氧化还原对更快的复合导致采用 SnO2 薄膜的 DSSC 暗电流增加，从而限制了器件的开路电压。正如该反应的瞬态吸收研究所证实的那样，染料阳离子的更快复合动力学导致氧化还原对染料基态再生效率显着降低，并且导致器件短路电流和填充因子损失。该损耗途径的重要性通过器件电流-电压数据的非理想二极管方程分析得到证实。添加MgO阻挡层被证明可有效减少氧化还原电解质的复合损失，但发现不能充分延迟染料阳离子的复合动力学以允许有效的染料再生而不导致电子注入效率的伴随损失。我们得出的结论是，由于氧化还原对的染料再生速率有限，DSSC 金属氧化物膜内电子动力学的如此大的加速通常可能不利于器件效率，并讨论了该结论对优化器件性能策略的影响。
We report a comparison of charge transport and recombination dynamics in dye-sensitized solar cells (DSSCs) employing nanocrystalline TiO2 and SnO2 films and address the impact of these dynamics upon photovoltaic device efficiency. Transient photovoltage studies of electron transport in the metal oxide film are correlated with transient absorption studies of electron recombination with both oxidized sensitizer dyes and the redox couple. For all three processes, the dynamics are observed to be 2-3 orders of magnitude faster for the SnO2 electrode. The origins of these faster dynamics are addressed by studies correlating the electron recombination dynamics to dye cations with chronoamperometric studies of film electron density. These studies indicate that the faster recombination dynamics for the SnO2 electrodes result both from a 100-fold higher electron diffusion constant at matched electron densities, consistent with a lower trap density for this metal oxide relative to TiO2, and from a 300 mV positive shift of the SnO2 conduction band/trap states density of states relative to TiO2. The faster recombination to the redox couple results in an increased dark current for DSSCs employing SnO2 films, limiting the device open-circuit voltage. The faster recombination dynamics to the dye cation result in a significant reduction in the efficiency of regeneration of the dye ground state by the redox couple, as confirmed by transient absorption studies of this reaction, and in a loss of device short-circuit current and fill factor. The importance of this loss pathway was confirmed by nonideal diode equation analyses of device current-voltage data. The addition of MgO blocking layers is shown to be effective at reducing recombination losses to the redox electrolyte but is found to be unable to retard recombination dynamics to the dye cation sufficiently to allow efficient dye regeneration without resulting in concomitant losses of electron injection efficiency. We conclude that such a large acceleration of electron dynamics within the metal oxide films of DSSCs may in general be detrimental to device efficiency due to the limited rate of dye regeneration by the redox couple and discuss the implications of this conclusion for strategies to optimize device performance.