Investigations of charge separation and migration in lead-free perovskite-based thin films and devices for photovoltaics using ultrafast broadband optical techniques and electrical characterization methods

在过去的几年里，铅基卤化物钙钛矿薄膜在光伏性能上表现出了惊人的提高，目前达到了超过22%的效率。然而，与水分和热分解以及由此产生的水溶性铅盐的毒性等有关的固有稳定性问题可能最终阻碍其广泛应用。因此，该领域的主要挑战之一是寻找具有良好光电性能的无毒且稳定的钙钛矿。这需要对载流子动力学和此类系统的光伏特性有深入的了解。在目前的提案中，它建立在Lenzer， Oum和Schlettwein小组先前对卤化物钙钛矿的研究基础上，因此，我们想要研究大量未开发的电荷载流子动力学和有前途的无铅钙钛矿薄膜和基于铋，锑，钯，锡和铟的器件。基于泵浦-超连续探针（PSCP）光谱/显微镜的强大时间分辨激光技术，覆盖从飞秒到毫秒的紫外-可见-近红外范围，将与适用于薄光伏活性层分析的电表征方法相结合，研究一组定义良好的钙钛矿薄膜和基于双钙钛矿和空位有序低维钙钛矿结构的器件。通过这种方式，我们将对光致载流子分离、输运、冷却和复合动力学有一个微观的认识。电学表征将针对界面中的体特性和接触形成，以及完整的太阳能电池，确定这些系统的电流-电压曲线，功率转换效率和外部量子效率的光谱依赖性。无铅钙钛矿的制备将采用湿化学方法，包括自旋镀膜、物理气相沉积和脉冲激光沉积方法。高质量的薄膜将沉积在一系列衬底上，以建立简单的钙钛矿界面系统，以及采用介孔和平面的n-i-p和p-i-n结构的完整光伏器件。除了之前资助期内使用的光谱学/显微镜技术外，我们将新实施PSCP宽带瞬态反射光谱：对于透明样品，这将与瞬态透射光谱同时使用，以确定反射率和透射率的变化。此外，这种新装置将使我们能够研究太阳能电池中强吸收和不透明的钙钛矿薄膜。

Over the last years, lead-based halide perovskite thin films have shown a phenomenal rise in photovoltaic performance, currently reaching efficiencies exceeding 22%. However, intrinsic stability problems related to, e.g., moisture and thermal decomposition as well as the toxicity of the resulting water-soluble lead salts might eventually hamper their widespread application. One of the main challenges in the field is therefore finding nontoxic and stable perovskites with good optoelectronic properties. This requires a deep understanding of the carrier dynamics and the photovoltaic properties of such systems. In the current proposal, which builds on previous studies by the Lenzer, Oum and Schlettwein groups on halide perovskites, we would therefore like to investigate the largely unexplored charge carrier dynamics and electrical properties of promising lead-free perovskite thin films and devices based on bismuth, antimony, palladium, tin and indium. Powerful time-resolved laser techniques based on pump - supercontinuum probe (PSCP) spectroscopy / microscopy covering the UV-Vis-NIR range over time scales from femtoseconds to milliseconds will be employed in combination with electrical characterization methods adapted to the analysis of thin photovoltaic active layers to investigate a well-defined set of perovskite thin films and devices based on double-perovskites and vacancy-ordered low-dimensional perovskite structures. This way we will obtain a microscopic understanding of the photoinduced charge carrier separation, transport, cooling and recombination dynamics. Electrical characterization will aim at the bulk properties and contact formation in the interfaces as well as at complete solar cells determining the current-voltage curves, power conversion efficiency and the spectral dependence of the external quantum efficiency of these systems. The lead-free perovskites will be prepared by wet-chemistry approaches involving spin-coating, physical vapor deposition and pulsed laser deposition methods. High-quality thin films will be deposited on a range of substrates to establish simple perovskite interface systems as well as complete photovoltaic devices employing n-i-p and p-i-n architectures, both mesoporous and planar. In addition to the spectroscopy / microscopy techniques used in the previous funding period, we will newly implement PSCP broadband transient reflection spectroscopy: For transparent samples, this will be simultaneously used with transient transmission spectroscopy to determine both, changes in reflectance and transmittance. In addition, this new setup will enable us to study the strongly absorbing and opaque perovskite thin films in solar cells.