Quantum Electronics Laboratory, Faculty of Physics, and ‡NanoBioMedical Centre, Adam Mickiewicz University in Poznań , Umultowska 85, 61-614 Poznań, Poland.
ACS Appl Mater Interfaces. 2017 May 24;9(20):17102-17114. doi: 10.1021/acsami.7b03288. Epub 2017 May 12.
The dynamics of electron transfer at the dye-titania and titania-electrolyte interfaces is investigated in two post-sensitization processes: (i) atomic layer deposition of blocking alumina coating and (ii) hierarchical molecular multicapping. To measure the electron transfer dynamics, time-resolved spectroscopic methods (femtosecond transient absorption on the time scale from femtoseconds to nanoseconds and electrochemical impedance spectroscopy on the time scale from milliseconds to seconds) are applied to the complete dye-sensitized solar cells with cobalt-based electrolyte and champion ADEKA-1 dye (with silyl-anchor unit) or its popular carboxyl-anchor analogue, MK-2 dye. Both molecular capping and alumina blocking layers slow down the electron injection process (the average rate constant decreases from 1.1 ps to 0.4 ps) and partial sub-nanosecond back electron transfer from titania to the dye (from ca. 10 ns to 5 ns). Very small alumina layers (of 0.1 nm thickness) have the highest impact on reducing the rate constants of these electron transfer processes, and for the thicknesses greater than 0.3 nm the rate constants hardly change. In contrast, the electron recombination between titania and electrolyte, occurring on the millisecond time scale, starts to be significantly suppressed for the blocking layers of 0.3 nm or more in thickness (up to ca. 20 times for 0.5 nm thickness with respect to that for untreated sample), improving open circuit voltage and fill factor of the cells. The amplitude of the relative photocurrent (short circuit current per number of absorbed photons) is found to depend almost exclusively on the ultrafast and fast processes taking place in the first nanoseconds after dye excitation. The positive impact of coadsorbents on the solar cells performance for both ADEKA-1 and MK-2 is also studied.
在两个后敏化过程中研究了染料-二氧化钛和二氧化钛-电解质界面处的电子转移动力学：（i）阻挡氧化铝涂层的原子层沉积和（ii）分级分子多封端。为了测量电子转移动力学，应用飞秒瞬态吸收（在飞秒到纳秒的时间尺度上）和电化学阻抗谱（在毫秒到秒的时间尺度上）两种时间分辨光谱方法对完整的钴基电解质染料敏化太阳能电池进行测试，所用染料为基于钴的电解质和冠军 ADEKA-1 染料（具有硅烷锚定单元）或其流行的羧酸锚定类似物 MK-2 染料。分子封端和氧化铝阻挡层都减慢了电子注入过程（平均速率常数从 1.1 ps 降低至 0.4 ps）和部分亚纳秒从二氧化钛到染料的反向电子转移（从约 10 ns 降低至 5 ns）。非常薄的氧化铝层（厚度为 0.1 nm）对降低这些电子转移过程的速率常数的影响最大，而对于厚度大于 0.3 nm 的氧化铝层，速率常数几乎不变。相反，在毫秒时间尺度上发生的钛和电解质之间的电子复合，对于厚度为 0.3 nm 或更大的阻挡层，开始受到明显抑制（对于 0.5 nm 厚度的阻挡层，相对于未处理的样品，抑制程度约为 20 倍），从而提高了电池的开路电压和填充因子。相对光电流的幅度（每吸收一个光子的短路电流）几乎仅取决于在染料激发后的最初 1 纳秒内发生的超快和快速过程。还研究了共吸附剂对 ADEKA-1 和 MK-2 太阳能电池性能的积极影响。
