Institute of Physical Chemistry , Polish Academy of Sciences , Kasprzaka 44/52 , 01-224 Warsaw , Poland.
J Am Chem Soc. 2018 Jun 13;140(23):7232-7238. doi: 10.1021/jacs.8b03191. Epub 2018 Jun 1.
Organic-inorganic lead halide perovskites are a promising family of light absorbers for a new generation of solar cells, with reported efficiencies currently exceeding 22%. A common problem of solar cells fabricated using these materials is that their efficiency depends on their cycling history, an effect known as current-voltage ( J- V) hysteresis. Potassium doping has recently emerged as a universal way to overcome this adverse phenomenon. While the atomistic origins of J- V hysteresis are still not fully understood, it is essential to rationalize the atomic-level effect of protocols that lead to its suppression. Here, using K MAS NMR at 21.1 T we provide for the first time atomic-level characterization of the potassium-containing phases that are formed upon KI doping of multication and multianion lead halide perovskites. We find no evidence of potassium incorporation into 3D perovskite lattices of the recently reported materials. Instead, we observe formation of a mixture of potassium-rich phases and unreacted KI. In the case of Br-containing lead halide perovskites doped with KI, a mixture of KI and KBr ensues, leading to a change in the Br/I ratio in the perovskite phase with respect to the undoped perovskite. Simultaneous Cs and K doping leads to the formation of nonperovskite Cs/K lead iodide phases.
有机-无机卤化铅钙钛矿是新一代太阳能电池有前途的光吸收剂家族，其报道的效率目前超过 22%。使用这些材料制造的太阳能电池的一个常见问题是，其效率取决于其循环历史，这种效应称为电流-电压（J-V）滞后。钾掺杂最近已成为克服这种不利现象的通用方法。虽然 J-V 滞后的原子起源仍不完全清楚，但对于导致其抑制的协议的原子水平效应进行合理化是至关重要的。在这里，我们使用 21.1 T 的 K MAS NMR 首次提供了在多阳离子和多阴离子卤化铅钙钛矿中用 KI 掺杂时形成的含钾相的原子水平表征。我们没有发现钾掺入最近报道的材料的 3D 钙钛矿晶格中的证据。相反，我们观察到富含钾的相和未反应的 KI 的形成。在用 KI 掺杂的含 Br 的卤化铅钙钛矿的情况下，会形成 KI 和 KBr 的混合物，从而导致钙钛矿相与未掺杂钙钛矿相比 Br/I 比发生变化。同时 Cs 和 K 掺杂会导致非钙钛矿 Cs/K 碘化铅相的形成。
