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，基于铅的卤化物钙钛矿薄膜在光伏性能方面有了显著的提高，目前效率达到了22%以上。然而，与水分和热分解等有关的固有稳定性问题以及由此产生的水溶性铅盐的毒性最终可能阻碍其广泛应用。因此，该领域的主要挑战之一是寻找无毒、稳定、具有良好光电性能的钙钛矿。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，我们基于Lenzer、Oum和Schlettwein小组之前对卤化物钙钛矿所做的研究，因此我们想要研究基于铋、锑、钯、锡和铟的有前途的无铅钙钛矿薄膜和器件的电荷载流子动力学和电学性质。基于泵浦-超连续谱(PSCP)光谱/显微镜的强大的时间分辨激光技术覆盖了从飞秒到毫秒的UV-VIS-NIR范围，将结合适合于分析薄光伏有源层的电学表征方法来研究一组定义良好的基于双钙钛矿和空位有序低维钙钛矿结构的钙钛矿薄膜和器件。通过这种方式，我们将对光生载流子的分离、输运、冷却和复合动力学有一个微观的了解。电学特性将针对界面和完整的太阳能电池中的体属性和接触形成，以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。无铅钙钛矿将通过湿化学方法制备，包括旋涂、物理气相沉积和脉冲激光沉积方法。将在一系列衬底上沉积高质量的薄膜，以建立简单的钙钛矿型界面系统以及采用n-i-p和p-i-n结构的完整光伏器件，包括介孔和平面结构。除了上一个资助期使用的光谱/显微技术外，我们还将新实施PSCP宽带瞬变反射光谱：对于透明样品，这将与瞬变透射光谱同时使用，以确定反射率和透射率的变化。此外，这种新的装置将使我们能够研究太阳能电池中的强吸收和不透明的钙钛矿型薄膜。

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.