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结构有序性和过剩能量在近红外宽带瞬态吸收实时探测的杂化聚噻吩/Si 光伏中超快自由电荷产生中的作用。

Role of structural order and excess energy on ultrafast free charge generation in hybrid polythiophene/Si photovoltaics probed in real time by near-infrared broadband transient absorption.

机构信息

Lehrstuhl für BioMolekulare Optik, Ludwig-Maximilians-Universität München, Oettingenstraße 67, 80538 München, Germany.

出版信息

J Am Chem Soc. 2011 Nov 16;133(45):18220-33. doi: 10.1021/ja207887q. Epub 2011 Oct 21.

Abstract

Despite the central role of light absorption and the subsequent generation of free charge carriers in organic and hybrid organic-inorganic photovoltaics, the precise process of this initial photoconversion is still debated. We employ a novel broadband (UV-Vis-NIR) transient absorption spectroscopy setup to probe charge generation and recombination in the thin films of the recently suggested hybrid material combination poly(3-hexylthiophene)/silicon (P3HT/Si) with 40 fs time resolution. Our approach allows for monitoring the time evolution of the relevant transient species under various excitation intensities and excitation wavelengths. Both in regioregular (RR) and regiorandom (RRa) P3HT, we observe an instant (<40 fs) creation of singlet excitons, which subsequently dissociate to form polarons in 140 fs. The quantum yield of polaron formation through dissociation of delocalized excitons is significantly enhanced by adding Si as an electron acceptor, revealing ultrafast electron transfer from P3HT to Si. P3HT/Si films with aggregated RR-P3HT are found to provide free charge carriers in planar as well as in bulk heterojunctions, and losses are due to nongeminate recombination. In contrast for RRa-P3HT/Si, geminate recombination of bound carriers is observed as the dominant loss mechanism. Site-selective excitation by variation of pump wavelength uncovers an energy transfer from P3HT coils to aggregates with a 1/e transfer time of 3 ps and reveals a factor of 2 more efficient polaron formation using aggregated RR-P3HT compared to disordered RRa-P3HT. Therefore, we find that polymer structural order rather than excess energy is the key criterion for free charge generation in hybrid P3HT/Si solar cells.

摘要

尽管光吸收在有机和杂化有机-无机光伏中起着核心作用,并且随后产生了自由电荷载流子,但这一初始光转换的确切过程仍存在争议。我们采用一种新的宽带(紫外可见近红外)瞬态吸收光谱装置,以 40 fs 的时间分辨率探测最近提出的杂化材料组合聚(3-己基噻吩)/硅(P3HT/Si)薄膜中的电荷产生和复合。我们的方法允许在不同的激发强度和激发波长下监测相关瞬态物种的时间演化。在规则(RR)和不规则(RRa)P3HT 中,我们都观察到单重激子的瞬间(<40 fs)形成,随后在 140 fs 内解离形成极化子。通过离域激子的解离形成极化子的量子产率通过添加 Si 作为电子受体而显著增强,这表明电子从 P3HT 到 Si 的超快转移。具有聚集 RR-P3HT 的 P3HT/Si 薄膜被发现可以在平面和体异质结中提供自由电荷载流子,并且损耗是由于非辐射复合引起的。相比之下,对于 RRa-P3HT/Si,观察到束缚载流子的复合是主要的损耗机制。通过改变泵浦波长进行的选择性激发揭示了从 P3HT 线圈到聚集体的能量转移,其转移时间为 3 ps,并表明使用聚集 RR-P3HT 比无序 RRa-P3HT 形成极化子的效率高 2 倍。因此,我们发现聚合物结构有序而不是多余的能量是在杂化 P3HT/Si 太阳能电池中产生自由电荷的关键标准。

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