Chemical Physics and NanoLund, Lund University , PO Box 118, 22100 Lund, Sweden.
School of Chemistry & Chemical Engineering, Key Laboratory of Mesoscopic Chemistry of MOE and Jiangsu Key Laboratory of Vehicle Emissions Control, Nanjing University , 22 Hankou Rd, Nanjing 210023, China.
ACS Nano. 2017 Jun 27;11(6):5391-5404. doi: 10.1021/acsnano.6b07407. Epub 2017 May 16.
Organo-metal halide perovskites are some of the most promising materials for the new generation of low-cost photovoltaic and light-emitting devices. Their solution processability is a beneficial trait, although it leads to a spatial inhomogeneity of perovskite films with a variation of the trap state density at the nanoscale. Comprehending their properties using traditional spectroscopy therefore becomes difficult, calling for a combination with microscopy in order to see beyond the ensemble-averaged response. We studied photoluminescence (PL) blinking of micrometer-sized individual methylammonium lead iodide (MAPbI) perovskite polycrystals, as well as monocrystalline microrods up to 10 μm long. We correlated their PL dynamics with structure employing scanning electron and optical super-resolution microscopy. Combining super-resolution localization imaging and super-resolution optical fluctuation imaging (SOFI), we could detect and quantify preferential emitting regions in polycrystals exhibiting different types of blinking. We propose that blinking in MAPbI occurs by the activation/passivation of a "supertrap" which presumably is a donor-acceptor pair able to trap both electrons and holes. As such, nonradiative recombination via supertraps, in spite being present at a rather low concentrations (10-10 cm), is much more efficient than via all other defect states present in the material at higher concentrations (10-10 cm). We speculate that activation/deactivation of a supertrap occurs by its temporary dissociation into free donor and acceptor impurities. We found that supertraps are most efficient in structurally homogeneous and large MAPbI crystals where carrier diffusion is efficient, which may therefore pose limitations on the efficiency of perovskite-based devices.
有机金属卤化物钙钛矿是新一代低成本光伏和发光器件最有前途的材料之一。它们的溶液可加工性是一个有益的特性，尽管这导致钙钛矿薄膜在纳米尺度上存在陷阱态密度的空间不均匀性。因此，使用传统光谱法理解它们的性质变得很困难，需要与显微镜结合，以便超越整体平均响应。我们研究了微米级单个甲脒碘化铅（MAPbI）钙钛矿多晶和长达 10μm 的单晶微棒的光致发光（PL）闪烁。我们利用扫描电子显微镜和光学超分辨率显微镜将其 PL 动力学与结构相关联。通过结合超分辨率定位成像和超分辨率光学波动成像（SOFI），我们可以在表现出不同类型闪烁的多晶体中检测和量化优先发射区域。我们提出，MAPbI 的闪烁是通过“超陷阱”的激活/失活引起的，超陷阱可能是一种既能捕获电子又能捕获空穴的施主-受主对。因此，尽管超陷阱的浓度（10-10 cm）相当低，但通过超陷阱的非辐射复合比通过材料中浓度更高的所有其他缺陷态（10-10 cm）要有效得多。我们推测，超陷阱的激活/失活是通过其暂时离解为自由施主和受主杂质来发生的。我们发现，超陷阱在结构均匀且载流子扩散效率高的大 MAPbI 晶体中效率最高，这可能会对基于钙钛矿的器件的效率造成限制。
