Nanocrystal Precursors to Doped Cesium Metal Halide Perovskite Photovoltaics

太阳是地球上最丰富的可持续能源的潜在来源。 用于发电的太阳能电池需要吸收太阳能并将其光子转化为电子的材料，这一过程称为光电子学。 最近，基于无机-有机卤化物钙钛矿材料的材料已经实现了接近硅太阳能电池的有前景的太阳能功率转换效率，并且可以使用低成本的基于溶液的制造方法由地球丰富的元素制成。 然而，目前的有机-无机钙钛矿光伏器件在空气中存在水分的情况下降解，并且有机组分是这种缺乏稳定性的一个原因。该项目的目标是开发完全由无机纳米晶体制成的新型钙钛矿太阳能电池材料。这种方法的创新之处在于，通过将含有铯和氯化物元素的不同类型的纳米晶体融合在一起，钙钛矿在水分中的稳定性将大大提高。作为与该项目相关的教育活动的一部分，太阳能光伏概念将被整合到宾夕法尼亚州费城费城材料日的实践演示中，作为加强STEM教学的州教育标准的一部分。本研究的总体目标是采用胶体纳米晶体的化学诱导烧结来生产用于太阳能光伏器件的铯金属卤化物钙钛矿的掺杂的多晶薄膜。 碘化铯铅和碘化铯锡钙钛矿相材料与用于太阳能光伏的混合有机/无机甲基铵碘化铅钙钛矿材料具有许多属性。 然而，相对于有机金属卤化物钙钛矿材料，全无机铯钙钛矿的挥发性和化学反应性都较低，但在大气水分的存在下仍然不稳定。 假设用氯化物掺杂将稳定钙钛矿形式的碘化铯铅。 为了进行氯化物掺杂，使用非均相反应烧结混合氯化铯铅和碘化铯铅纳米晶的固体膜。通过这种方法，可以合成非平衡，混合的双折射薄膜。 这种基于纳米晶的方法还使得有可能使用原位温度依赖性吸收光谱法跟踪合成反应的进展和产物，以在微观水平上检测混合和相分离，从而阐明动力学与化学控制过程。 这里提出的分析方法提供了一个机会，以机械地理解两种不同的卤化物钙钛矿相的固有的相容性，以促进混合晶体钙钛矿薄膜的整体相稳定性。

The sun represents the most abundant potential source of sustainable energy on earth. Solar cells for producing electricity require materials that absorb the sun's energy and convert its photons to electrons, a process called photovoltaics. Recently, materials based on inorganic-organic halide perovskite materials have achieved promising solar energy power conversion efficiency approaching that of silicon solar cells, and can be made from earth-abundant elements using lower-cost, solution based fabrication methods. However, present organic-inorganic perovskite photovoltaic devices degrade in the presence of moisture in air, and the organic component is one reason for this lack of stability. The goal of this project is develop new class of perovskite solar cell materials that are made entirely of inorganic, nanometer sized crystals. The innovative aspect of this approach is that by fusing together different types of nanocrystals which contain the elements cesium and chloride, the stability of the perovskite in moisture will be much improved. As part of the educational activities associated with this project, solar photovoltaic concepts will be integrated into hands-on demos at Philly Materials Day in Philadelphia, PA, as part of an effort to reinforce state education standards in STEM teaching. The overall goal of this research is to employ chemically-induced sintering of colloidal nanocrystals to produce doped, polycrystalline thin films of cesium metal halide perovskites for use in solar photovoltaic devices. Cesium lead iodide and cesium tin iodide perovskite phase materials share many attributes with the hybrid organic/inorganic methylammonium lead iodide perovskite materials for solar photovoltaics. However, relative to organic metal halide perovskite materials, the all-inorganic cesium perovskites are both less volatile and less chemically reactive, but are still not stable in the presence of atmospheric moisture. It is hypothesized that doping with chloride will stabilize the cesium lead iodide in the perovskite form. To carry out the chloride doping, a hetergenous-phase reaction is used to sinter solid films of mixed cesium lead chloride and cesium lead iodide nanocrystals. By this approach, non-equilibrium, mixed nanocrystal thin films can be synthesized. This nanocrystal-based approach also makes it possible to follow the progress and products of the synthesis reactions with in-situ, temperature-dependent absorption spectroscopy to detect both mixing and phase-separation at microscopic levels, allowing for elucidation of kinetically vs. thermodynamically controlling processes. The analytical approaches proposed here present an opportunity to mechanistically understand the intrinsic miscibility of two dissimilar halide perovskite phases to promote the overall phase stability of mixed crystal perovskite thin films.