Grancini Giulia, Viola Daniele, Lee Yonghui, Saliba Michael, Paek Sanghyun, Cho Kyung Taek, Orlandi Simonetta, Cavazzini Marco, Fungo Fernando, Hossain Mohammad I, Belaidi Abdelhak, Tabet Nouar, Pozzi Gianluca, Cerullo Giulio, Nazeeruddin Mohammad Khaja
Group for Molecular Engineering of Functional Materials, Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne, 1951, Sion, Switzerland.
Istituto di Fotonica e Nanotecnologie del CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133, Milano, Italy.
Chemphyschem. 2017 Sep 6;18(17):2381-2389. doi: 10.1002/cphc.201700492. Epub 2017 Jul 19.
With a power conversion efficiency (PCE) exceeding 22 %, perovskite solar cells (PSCs) have thrilled photovoltaic research. However, the interface behavior is still not understood and is a hot topic of research: different processes occur over a hierarchy of timescales, from femtoseconds to seconds, which makes perovskite interface physics intriguing. Herein, through femtosecond transient absorption spectroscopy with spectral coverage extending into the crucial IR region, the ultrafast interface-specific processes at standard and newly molecularly engineered perovskite interfaces in state-of-the-art PSCs are interrogated. Ultrafast interfacial charge injection occurs with a time constant of 100 fs, resulting in hot transfer from energetic charges and setting the timescale for the first step involved in the complex charge-transfer process. This is also true for 20 % efficient devices measured under real operation, for which the femtosecond injection is followed by a slower picosecond component. These findings provide compelling evidence for the femtosecond interfacial charge-injection step and demonstrate a robust method for the straightforward identification of interfacial non-equilibrium processes on the ultrafast timescale.
钙钛矿太阳能电池（PSCs）的功率转换效率（PCE）超过22%，这令光伏研究领域为之振奋。然而，其界面行为仍未得到充分理解，仍是一个研究热点：从飞秒到秒的不同时间尺度上会发生不同过程，这使得钙钛矿界面物理引人入胜。在此，通过飞秒瞬态吸收光谱，其光谱覆盖范围延伸至关键的红外区域，对最先进的PSCs中标准和新分子工程化钙钛矿界面的超快界面特定过程进行了研究。超快界面电荷注入的时间常数为100飞秒，导致高能电荷发生热转移，并为复杂电荷转移过程中第一步设定了时间尺度。对于在实际运行条件下测量的20%效率的器件也是如此，其飞秒注入之后是较慢的皮秒成分。这些发现为飞秒界面电荷注入步骤提供了有力证据，并展示了一种在超快时间尺度上直接识别界面非平衡过程的可靠方法。
