Department of Chemistry, University of Toronto , 80 St. George Street, Toronto, Ontario, Canada , M5S 3G4.
The Edward S. Rogers Department of Electrical and Computer Engineering, University of Toronto , 10 King's College Road, Toronto, Ontario, Canada , M5S 3G4.
J Am Chem Soc. 2018 Feb 28;140(8):2890-2896. doi: 10.1021/jacs.7b12551. Epub 2018 Feb 16.
Metal halide perovskites have achieved photovoltaic efficiencies exceeding 22%, but their widespread use is hindered by their instability in the presence of water and oxygen. To bolster stability, researchers have developed low-dimensional perovskites wherein bulky organic ligands terminate the perovskite lattice, forming quantum wells (QWs) that are protected by the organic layers. In thin films, the width of these QWs exhibits a distribution that results in a spread of bandgaps in the material arising due to varying degrees of quantum confinement across the population. Means to achieve refined control over this QW width distribution, and to examine and understand its influence on photovoltaic performance, are therefore of intense interest. Here we show that moving to the ligand allylammonium enables a narrower distribution of QW widths, creating a flattened energy landscape that leads to ×1.4 and ×1.9 longer diffusion lengths for electrons and holes, respectively. We attribute this to reduced ultrafast shallow hole trapping that originates from the most strongly confined QWs. We observe an increased PCE of 14.4% for allylammonium-based perovskite QW photovoltaics, compared to 11-12% PCEs obtained for analogous devices using phenethylammonium and butylammonium ligands. We then optimize the devices using mixed-cation strategies, achieving 16.5% PCE for allylammonium devices. The devices retain 90% of their initial PCEs after >650 h when stored under ambient atmospheric conditions.
金属卤化物钙钛矿已实现超过 22%的光电效率，但由于其在水和氧气存在下的不稳定性，其广泛应用受到阻碍。为了提高稳定性，研究人员开发了低维钙钛矿，其中庞大的有机配体终止了钙钛矿晶格，形成了量子阱（QW），由有机层保护。在薄膜中，这些 QW 的宽度表现出分布，导致材料的能带隙因量子限制程度的不同而分散。因此，实现对这种 QW 宽度分布的精细控制，并研究和理解其对光伏性能的影响，是非常有意义的。在这里，我们表明，采用烯丙基铵配体可以实现更窄的 QW 宽度分布，从而形成更平坦的能量景观，分别使电子和空穴的扩散长度延长了 1.4 倍和 1.9 倍。我们将这归因于起源于最受限制的 QW 的超快浅孔捕获的减少。我们观察到基于烯丙基铵的钙钛矿 QW 光伏器件的 PCE 增加到 14.4%，而使用苯乙基铵和丁基铵配体的类似器件的 PCE 为 11-12%。然后，我们使用混合阳离子策略对器件进行优化，使烯丙基铵器件的 PCE 达到 16.5%。在环境大气条件下储存 >650 h 后，器件保留了初始 PCE 的 90%。
