Hoffman Justin M, Malliakas Christos D, Sidhik Siraj, Hadar Ido, McClain Rebecca, Mohite Aditya D, Kanatzidis Mercouri G
Department of Chemistry, Northwestern University Evanston IL 60208 USA
Department of Chemical and Biomolecular Engineering, Rice University Houston Texas 77005 USA.
Chem Sci. 2020 Oct 6;11(44):12139-12148. doi: 10.1039/d0sc04144k.
Two-dimensional (2D) halide perovskites have great promise in optoelectronic devices because of their stability and optical tunability, but the subtle effects on the inorganic layer when modifying the organic spacer remain unclear. Here, we introduce two homologous series of Ruddlesden-Popper (RP) structures using the branched isobutylammonium (IBA) and isoamylammonium (IAA) cations with the general formula (RA)(MA) Pb I (RA = IBA, IAA; MA = methylammonium = 1-4). Surprisingly, the IAA = 2 member results in the first modulated 2D perovskite structure with a ripple with a periodicity of 50.6 Å occurring in the inorganic slab diagonally to the [101] direction of the basic unit cell. This leads to an increase of Pb-I-Pb angles along the direction of the wave. Generally, both series show larger in-plane bond angles resulting from the additional bulkiness of the spacers compensating for the MA's small size. Larger bond angles have been shown to decrease the bandgap which is seen here with the bulkier IBA leading to both larger in-plane angles and lower bandgaps except for = 2, in which the modulated structure has a lower bandgap because of its larger Pb-I-Pb angles. Photo-response was tested for the = 4 compounds and confirmed, signaling their potential use in solar cell devices. We made films using an MACl additive which showed good crystallinity and preferred orientation according to grazing-incidence wide-angle scattering (GIWAXS). As exemplar, the two = 4 samples were employed in devices with champion efficiencies of 8.22% and 7.32% for IBA and IAA, respectively.
二维（2D）卤化物钙钛矿因其稳定性和光学可调性在光电器件中具有巨大潜力，但在修饰有机间隔基时对无机层的微妙影响仍不清楚。在这里，我们引入了两个同系的Ruddlesden-Popper（RP）结构系列，使用支链异丁基铵（IBA）和异戊基铵（IAA）阳离子，通式为（RA）（MA）PbI（RA = IBA，IAA；MA = 甲铵 = 1 - 4）。令人惊讶的是，IAA = 2的成员导致了第一个调制的2D钙钛矿结构，在无机平板中出现了与基本晶胞[101]方向对角的周期性为50.6 Å的波纹。这导致沿波方向的Pb - I - Pb角增加。一般来说，这两个系列都显示出较大的面内键角，这是由于间隔基额外的体积补偿了MA的小尺寸。已表明较大的键角会降低带隙，在这里可以看到，除了 = 2的情况外，体积更大的IBA导致更大的面内角度和更低的带隙，在 = 2的情况下，调制结构由于其更大的Pb - I - Pb角而具有更低的带隙。对 = 4的化合物进行了光响应测试并得到证实，表明它们在太阳能电池器件中的潜在用途。我们使用MACl添加剂制备了薄膜，根据掠入射广角散射（GIWAXS）显示出良好的结晶度和择优取向。作为示例，两个 = 4的样品分别用于器件中，IBA和IAA的最佳效率分别为8.22%和7.32%。
