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方面表现出惊人的增长，目前效率超过22%。然而，固有的稳定性问题，例如，湿气和热分解以及所得水溶性铅盐的毒性可能最终阻碍它们的广泛应用。因此，该领域的主要挑战之一是找到具有良好光电性能的无毒且稳定的钙钛矿。这就需要深入了解载流子动力学和光伏特性的这种系统。在当前的提案中，该提案建立在Lenzer，Oum和Schlettwein小组对卤化物钙钛矿的先前研究的基础上，因此，我们希望研究基于铋，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-超连续谱探测（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时间尺度上的UV-Vis-NIR范围，将与适用于分析薄光伏有源层的电学表征方法相结合，以研究一组定义明确的钙钛矿薄膜和基于双钙钛矿和空位有序的低密度半导体器件。三维钙钛矿结构。通过这种方式，我们将获得光致载流子分离，运输，冷却和复合动力学的微观理解。电气特性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。高质量的薄膜将沉积在一系列基板上，以建立简单的钙钛矿界面系统，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。除了上一个资助期使用的光谱/显微镜技术外，我们还将新实施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，这种新的设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.