Dipartimento di Fisica "E.R. Caianiello" and CNR-SPIN Salerno, Università di Salerno, I-84084 Fisciano, Salerno, Italy.
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Institut für Silizium Photovoltaik, Kekuléstr. 5, 12489 Berlin, Germany.
Sci Rep. 2016 Oct 5;6:34675. doi: 10.1038/srep34675.
The hybrid perovskite methylammonium lead iodide CHNHPbI recently revealed its potential for the manufacturing of low-cost and efficient photovoltaic cells. However, many questions remain unanswered regarding the physics of the charge carrier conduction. In this respect, it is known that two structural phase transitions, occurring at temperatures near 160 and 310 K, could profoundly change the electronic properties of the photovoltaic material, but, up to now, a clear experimental evidence has not been reported. In order to shed light on this topic, the low-temperature phase transition of perovskite solar cells has been thoroughly investigated by using electric noise spectroscopy. Here it is shown that the dynamics of fluctuations detect the existence of a metastable state in a crossover region between the room-temperature tetragonal and the low-temperature orthorhombic phases of the perovskite compound. Besides the presence of a noise peak at this transition, a saturation of the fluctuation amplitudes is observed induced by the external DC current or, equivalently, by light exposure. This noise saturation effect is independent on temperature, and may represent an important aspect to consider for a detailed explanation of the mechanisms of operation in perovskite solar cells.
最近，混合钙钛矿碘化甲基铵铅（CHNHPbI）因其可用于制造低成本、高效率的光伏电池而备受关注。然而，关于电荷载流子输运的物理性质仍存在许多未解之谜。在这方面，人们已经知道，两种结构相变（在接近 160 和 310 K 的温度下发生）可能会深刻地改变光伏材料的电子特性，但到目前为止，还没有明确的实验证据对此进行报道。为了阐明这一问题，人们通过使用电噪声谱学对钙钛矿太阳能电池的低温相变进行了彻底的研究。研究结果表明，在钙钛矿化合物的室温四方相和低温正交相之间的交叉区域，波动的动力学检测到了亚稳态的存在。除了在这个相变处存在噪声峰值外，还观察到了由外部直流电流或等效的光照射引起的波动幅度的饱和。这种噪声饱和效应与温度无关，对于详细解释钙钛矿太阳能电池的工作机制可能是一个重要的考虑因素。
