Bowman Alan R, Stranks Samuel D, Monserrat Bartomeu
Cavendish Laboratory, Department of Physics, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0HE, U.K.
Department of Chemical Engineering and Biotechnology, University of Cambridge, Philippa Fawcett Drive, Cambridge CB3 0AS, U.K.
Chem Mater. 2022 Jun 14;34(11):4865-4875. doi: 10.1021/acs.chemmater.1c04310. Epub 2022 May 16.
A method for improving the efficiency of solar cells is combining a low-band-gap semiconductor with a singlet fission material (which converts one high-energy singlet into two low-energy triplets following photoexcitation). Here, we present a study of the interface between singlet fission molecules and low-band-gap halide pervoskites. We briefly present 150 experiments screening for triplet transfer into a halide perovskite. However, in all cases, triplet transfer was not observed. This motivated us to understand the halide perovskite-singlet fission interface better by carrying out first-principles calculations using tetracene and cesium lead iodide. We found that tetracene molecules/thin films preferentially orient themselves parallel to/perpendicular to the halide perovskite's surface. This result is in agreement with simulations of tetracene (and other rodlike molecules) on a wide range of inorganic semiconductors. We present formation energies of all interfaces, which are significantly less favorable than for bulk tetracene, indicative of weak interaction at the interface. It was not possible to calculate excitonic states at the full interface due to computational limitations, so we instead present highly speculative toy interfaces between tetracene and a halide-perovskite-like structure. In these models, we focus on replicating tetracene's electronic states correctly. We find that tetracene's singlet and triplet energies are comparable to that of bulk tetracene, and the triplet is strongly localized on a single tetracene molecule, even at an interface. Our work provides new understanding of the interface between tetracene and halide perovskites, explores the potential for modeling excitons at interfaces, and begins to explain the difficulties in extracting triplets directly into inorganic semiconductors.
一种提高太阳能电池效率的方法是将低带隙半导体与单线态裂变材料相结合（该材料在光激发后将一个高能单线态转化为两个低能三线态）。在此，我们展示了一项关于单线态裂变分子与低带隙卤化物钙钛矿之间界面的研究。我们简要介绍了150次筛选三线态向卤化物钙钛矿转移的实验。然而，在所有情况下，均未观察到三线态转移。这促使我们通过使用并四苯和碘化铯铅进行第一性原理计算，来更好地理解卤化物钙钛矿 - 单线态裂变界面。我们发现并四苯分子/薄膜优先平行于/垂直于卤化物钙钛矿的表面取向。这一结果与并四苯（以及其他棒状分子）在多种无机半导体上的模拟结果一致。我们展示了所有界面的形成能，这些形成能明显不如体相并四苯有利，表明界面处相互作用较弱。由于计算限制，无法计算整个界面的激子态，因此我们转而展示并四苯与类卤化物钙钛矿结构之间高度推测性的简化界面。在这些模型中，我们专注于正确复制并四苯的电子态。我们发现并四苯的单线态和三线态能量与体相并四苯相当，并且即使在界面处，三线态也强烈定域在单个并四苯分子上。我们的工作为并四苯与卤化物钙钛矿之间的界面提供了新的认识，探索了在界面处对激子进行建模的潜力，并开始解释直接将三线态提取到无机半导体中的困难。
