Interfaces, Stability and Energy Efficiency: Photochemical Characterisation of Perovskites for Printable Photovoltaics

清洁能源是人类在21世纪世纪面临的最重要的科技挑战。对气候变化、能源独立和不可再生能源储备枯竭的担忧正在推动世界各国政府制定和实施替代能源政策和技术。为了满足人类当前日益增长的能源需求，发展低成本、大面积、稳定的光致发光器件势在必行。当前的光伏（PV）市场由晶体硅模块（>当前PV市场的85%）主导。尽管最近主流硅PV的制造成本大幅降低，但PV技术存在明显的机会，这些PV技术可以显著提高功率能量转换效率（PCE）或显著降低处理成本（在财务和嵌入式能源方面）。基于钙钛矿的太阳能电池在这两方面都有前景。基于Peroxide的太阳能电池是一种相对年轻的技术，在2009年首次报道，并且隐喻地打开了一种令人兴奋的、新的、高效的固态光伏技术的大门，该技术可以与需要真空沉积和/或昂贵的非平凡处理的硅和薄膜技术竞争。然而，稳定性和寿命问题必须得到理解和克服，以推动该领域的发展。在这里，我们的目标是研究可印刷钙钛矿光致发光材料的光化学和稳定性，目的是了解适合大规模生产的材料。该项目将专注于开发管理钙钛矿材料的光致发光（PL）特性的基本过程的详细了解。钙钛矿薄膜的PL并不像最初想象的那样简单，突出了这些材料有时令人惊讶的性质，在这里，我们试图解开PL数据，并讨论这可以告诉我们关于这些材料的信息。我们将研究一系列的钙钛矿通过荧光显微镜（FM）耦合光纤光谱仪。这允许精确控制测量环境（温度和气氛控制），并提供关于本体和局部光致发光（PL）的信息，并允许我们绘制薄膜表面，并监测暴露于各种受控环境下的光致发光随时间的演变。Percent材料往往对空气/水分、光和氧气敏感。分子氧可能是特别成问题的，因为半导体表面处的光生电子将氧还原成自由基物质和空穴，自由基物质和空穴对器件具有极强的反应性并且可能导致器件的快速劣化。我们的目标是关联的PL，PL随时间的变化，与整体光伏器件的效率和稳定性。这是一种快速而直接的筛选方法，不需要制造完整的设备来评估和优化钙钛矿性能。这将提供急需的了解这些设备的稳定性，并提供了一个明确的路线，优化和提高设备的稳定性。时间分辨PL提供的电荷载流子动力学和提取的重要信息（在电荷选择性接触的存在下），这是一个关键的性能指标。我们的目的是实现一个全球性的理解的载流子寿命和提取，实现通过严格控制的所有组件的载流子-电荷选择性接触界面，并通过这样的接口发生的电荷转移过程的动力学的评价。然后可以设计/定制电荷接触以最大化电导率，同时最小化背电子转移和复合，从而提高器件性能。

The clean generation of energy is the most important scientific and technological challenge that faces humankind in the 21st century. Concerns about climate change, energy independence, and depletion of non-renewable reserves, are pushing governments around the world to develop and implement alternative-energy policies and technologies. The development of low-cost, large area, stable photovoltaics is an absolute must to meet humankinds' current, growing, energy need. The current photovoltaic (PV) market, is dominated by crystalline silicon modules (> 85 % of the present PV market). Despite the recent substantial reductions in the manufacturing cost of mainstream silicon PV, there exists clear opportunities for PV technologies that promise either significant higher power energy conversion efficiencies (PCE) or significantly lower processing costs (both in financial and embodied energy terms). Perovskite-based solar cells, offer prospects on both fronts. Perovskite based solar cells are a relatively young technology, first reported in 2009, and have metaphorically opened the door to an exciting, new, highly efficient solid-state photovoltaic technology which could compete with silicon and thin film technologies that require vacuum deposition and/or expensive non-trivial processing. However, stability and lifetime issues must be understood and overcome to progress the field.Here we aim to look at the photochemistry and stability of printable perovskite photovoltaics with the aim to develop an understanding of materials that are suitable to manufacture at a large scale. This project will focus on developing a detailed understanding of the fundamental processes that govern the photoluminescence (PL) properties of perovskite materials. PL of perovskite thin-films is not as straightforward as initially thought highlighting the sometimes-surprising nature of these materials, here we attempt to unravel the PL data and discuss what this can tell us about these materials. We will study a series of perovskites via fluorescence microscopy (FM) coupled with an optical fibre spectrometer. This allows precise control of the measurement environment (temperature and atmosphere control) and provides information on the bulk and local photoluminescence (PL) and allows us to map the surface of the films and monitor the evolution of photoluminescence with time exposed to various controlled environments. Perovskite materials tend to be sensitive to air/moisture, light and oxygen. Molecular oxygen can be particularly problematic as photo-generated electrons at a semiconductor surface reduce oxygen to radical species and holes which are extremely reactive towards and can result in rapid degradation of devices. We aim to correlate the PL, and the changes in PL with time, with the overall PV device efficiency and stability. This is a rapid and straight forward screening method that does not need the manufacture of a complete device to evaluate and optimise the perovskite properties. This will provide much needed understanding of the stability of these devices and deliver a clear route for the optimisation and improvement of device stability.Time resolved PL provides vital information on the charge carrier kinetics and extraction (in the presence of charge selective contacts) which is a key indicator of performance. The aim is to achieve a global understanding of the charge carrier lifetime and extraction, achieved through a rigorous control of all the components of the absorber-charge selective contact interface, and an evaluation of the kinetics of charge transfer processes occurring through such interfaces. Charge contacts can then be designed/tailored to maximise conductivity, while minimising back electron transfer and recombination and thus improving device performance.