Institut des Sciences et Ingénierie Chimiques , Ecole Polytechnique Fédérale de Lausanne (EPFL), EPFL-BCH , CH-1015 Lausanne , Switzerland.
Department of Materials Science and Engineering , Sharif University of Technology , 14588 Tehran , Iran.
Nano Lett. 2018 Apr 11;18(4):2428-2434. doi: 10.1021/acs.nanolett.7b05469. Epub 2018 Mar 15.
The solar to electric power conversion efficiency (PCE) of perovskite solar cells (PSCs) has recently reached 22.7%, exceeding that of competing thin film photovoltaics and the market leader polycrystalline silicon. Further augmentation of the PCE toward the Shockley-Queisser limit of 33.5% warrants suppression of radiationless carrier recombination by judicious engineering of the interface between the light harvesting perovskite and the charge carrier extraction layers. Here, we introduce a mesoscopic oxide double layer as electron selective contact consisting of a scaffold of TiO nanoparticles covered by a thin film of SnO, either in amorphous (a-SnO), crystalline (c-SnO), or nanocrystalline (quantum dot) form (SnO-NC). We find that the band gap of a-SnO is larger than that of the crystalline (tetragonal) polymorph leading to a corresponding lift in its conduction band edge energy which aligns it perfectly with the conduction band edge of both the triple cation perovskite and the TiO scaffold. This enables very fast electron extraction from the light perovskite, suppressing the notorious hysteresis in the current-voltage ( J-V) curves and retarding nonradiative charge carrier recombination. As a result, we gain a remarkable 170 mV in open circuit photovoltage ( V ) by replacing the crystalline SnO by an amorphous phase. Because of the quantum size effect, the band gap of our SnO-NC particles is larger than that of bulk SnO causing their conduction band edge to shift also to a higher energy thereby increasing the V . However, for SnO-NC there remains a barrier for electron injection into the TiO scaffold decreasing the fill factor of the device and lowering the PCE. Introducing the a-SnO coated mp-TiO scaffold as electron extraction layer not only increases the V and PEC of the solar cells but also render them resistant to UV light which forebodes well for outdoor deployment of these new PSC architectures.
钙钛矿太阳能电池 (PSC) 的太阳能到电能转换效率 (PCE) 最近达到了 22.7%，超过了竞争的薄膜光伏和市场领先的多晶硅。通过明智地工程设计光捕获钙钛矿和电荷载流子提取层之间的界面，可以进一步提高 PCE 以达到肖克利-奎塞尔极限 33.5%。在这里，我们引入介观氧化物双层作为电子选择接触，由 TiO 纳米粒子的支架组成，该支架覆盖有 SnO 的薄膜，无论是非晶态 (a-SnO)、晶态 (c-SnO) 还是纳米晶态 (量子点) 形式 (SnO-NC)。我们发现，a-SnO 的能带隙大于晶态 (四方晶相) 多晶型体，导致其导带边缘能相应升高，使其与三阳离子钙钛矿和 TiO 支架的导带边缘完全匹配。这使得电子可以从光钙钛矿中非常快速地提取出来，抑制了电流-电压 (J-V) 曲线中众所周知的滞后，并减缓了非辐射电荷载流子的复合。因此，通过用非晶相取代晶态 SnO，我们在开路光电压 (V) 中获得了显著的 170 mV 的增益。由于量子尺寸效应，我们的 SnO-NC 颗粒的能带隙大于体相 SnO，导致其导带边缘也向更高的能量移动，从而增加了 V。然而，对于 SnO-NC，电子注入到 TiO 支架中仍然存在障碍，降低了器件的填充因子并降低了 PCE。引入涂覆有 mp-TiO 的 a-SnO 作为电子提取层不仅增加了太阳能电池的 V 和 PEC，而且还使它们能够抵抗紫外线，这预示着这些新的 PSC 结构可以在户外得到很好的应用。
