應用於鈣鈦礦光伏元件之半導體材料其結晶控制及研究

在本篇論文中，我們的研究目標主要著眼在組成鈣鈦礦光伏元件中的幾種半導體材料。近年來，鈣鈦礦光伏元件的技術和元件表現迅速成長，被認為能發展出一項極具潛力的太陽能產業。為了將這項技術由學術界轉移至產業界，以利在未來更進一步商業化，快速而大面積的生產高效能鈣鈦礦光伏元件或模組便成為一項相當重要的課題。為了要達成此一目標，不僅要能夠對材料本質特性有更加深入的研究和了解，同時也要能開發出有效且節能的薄膜鍍膜方式。在研究材料本質特性方面，可以利用單晶低缺陷密度的特性，將其作為一個相當好的研究平台和對象。此外，了解並調控材料在結晶時的過程和反應可以幫助更有效的形成高結晶性的薄膜。因此，我們由控制結晶的想法出發，研究了包括有機無機鈣鈦礦和氧化物薄膜等材料，期望這份研究能夠深入探討鈣鈦礦的特性、提供了解鈣鈦礦特性的手段、以及開發出利於量化生產的製程，為鈣鈦礦光伏元件邁向產業化鋪路。有機無機鈣鈦礦單晶在做為各種光電元件的應用上展現出極高的潛力。晶面的品質對於元件表現具有相當程度的影響。此外，亦有報導推斷在鈣鈦礦材料上，不同晶面可以展現出不同的光電表現。目前有許多團隊開發出各種成長鈣鈦礦單晶的手段，然而，礙於沒有一種方式可以有效而精確的調控鈣鈦礦單晶其暴露的晶面種類和比例，在有機無機鈣鈦礦這個研究領域中，不同晶面對於光電乃至於其他特性的影響仍不明確。在本研究中，我們提供一種相當簡易、利用配位基控制表面能，進一步控制單晶暴露晶面的單晶成長方式。在鈣鈦礦單晶成長溶液中，逐量增加油胺濃度時，可以發現單晶的形狀逐漸由常見十二面體轉為立方體，相對應的暴露晶面也由原本的(100)和(112)轉變為(110)和(002)。經由進一步的鑑定可知，該單晶的組成成分和結構並不因油胺濃度的影響而有所差別。因此，藉由這種方法，我們確實可以在排除其他可能影響因素的情況下，研究鈣鈦礦材料其不同晶面對於光電特性的影響。為了驗證這一概念，我們以不同晶面的鈣鈦礦單晶製作了光偵測器。因此，這項研究結果可幫助人們更加了解鈣鈦礦材料的本質特性。在鈣鈦礦光伏元件中，金屬氧化物常被選作為載子選擇層。利用合適的金屬氧化物，鈣鈦礦光伏元件可以展現出更高的元件效率與更長的操作壽命。溶膠凝膠法因為具有低成本、易於量產、對環境無害等特性，不論是在學術界或工業界，皆常被用於製備各種氧化物薄膜。在採用溶膠凝膠法將有機金屬前驅物轉化為具結晶之金屬氧化物時，一般需使用較高的燒結溫度和較長的燒結時間。為了降低製程的熱預算以及生產成本以便拓寬基材的選擇條件和開發更多的應用，我們對於氧化物的溶膠凝膠法進行一系列的研究。我們發現藉由添加四甲基氫氧化銨於溶膠凝膠前驅物溶液中，在加熱的過程中，由四甲基氫氧化銨釋放出的氫氧根能夠快速地跟有機金屬前驅物反應，生成金屬氫氧化物。在提升了金屬氫氧化物的生成速度後，金屬氧化物也可以更快速的生成。利用這種方法，溶膠凝膠反應所需的溫度和時間都可大幅地降低。在製備應用於鈣鈦礦光伏元件的氧化物薄膜時，熱處理的溫度可以降低將近50 oC，而熱處理的時間也可以縮短至原先的一半。除此之外，由於該方法並沒有對金屬元素有特定的選擇性，因此具有相當的潛力可以廣泛運用在各種以溶膠凝膠法製備的金屬氧化物上。我們實作並證明了氧化鎳、氧化鈷、氧化銅、氧化鈦、以及氧化銦皆可以透過此一方式降低反應的溫度與時間。因此這項研究提供了一種節能且有效的製備高結晶性氧化物薄膜的方法。

關鍵字

鈣鈦礦太陽能電池；單晶；晶面工程；氧化物薄膜；低溫製程

並列摘要

In this dissertation, we focus on the semiconducting materials for the fabrication of perovskite photovoltaics. The emerging perovskite photovoltaics is an appealing high performance and low cost technology which may revolutionize the photovoltaic society. In order to commercialize this new technology, high efficiency perovskite photovoltaics made from large-scale high-throughput solution process need to be realized. To achieve this goal, not only a thorough research on the material properties but also an energy conservative deposition strategy are required. Controlling the single crystal growth process can give us more insight into the intrinsic material properties. In addition, understanding and modulating the procedures of crystallization can lead to efficient formation of highly crystalline thin film. Therefore, we start from the perspective of crystallization control including organic inorganic hybrid perovskite and metal oxide thin film, hoping our study can unveil the fundamental characteristics of those materials and dictate promising approaches to the commercialization of perovskite photovoltaics. Organic inorganic hybrid perovskite single crystals are potential materials for the application of high performance optoelectronic devices. The exposed surface of single crystals can dramatically affect the measured properties. Facet-dependent behaviors are also speculated. However, impeded by the lack of facile facet engineering strategy for inorganic organic hybrid perovskites, the relationship between different facets and respective performance remains elusive. In this work, we present a simple approach of ligand-mediated crystal growth to control the shape and the exposed facets of methylammonium lead iodide single crystals. The addition of oleylamine ligand can trigger the continuous morphological transition from dodecahedral-shaped single crystal enclosed by (100)T and (112)T to cubic-shaped single crystal enclosed by (110)T and (002)T while maintaining the material composition and crystalline phase. The mechanism governs the facet engineering phenomenon was investigated. We fabricated single crystal based photodetectors and carried out the first unambiguous study on the relationship between facet structure and device performance. This report opens a new paradigm to reveal the facet-dependent properties and to enhance the device performance of single crystal. Using metal oxide thin films in perovskite photovoltaics as selective layer can lead to the devices with high energy conversion efficiency and long-term stability. Bearing the advantages such as cost-effective, large-scalable, well-established, and environmentally benign, sol-gel chemistry is widely used across academy and industry to fabricate metal oxide thin films. In typical sol-gel process, high annealing temperature and long annealing time are usually required to transform amorphous organometal precursor into crystalline metal oxide. Reducing the thermal budget required for their crystallization process can relax the fabrication limitation and expand their possible applications. We show that with the addition of adequate amount of tetramethylammonium hydroxide in precursor solution, not only the required thermal treatment time and temperature for sol-gel reaction can be significantly reduced but also the quality of the film can be improved. The enhanced reaction rate can be ascribed to the presence of hydroxyl anions, which facilitates the formation of metal hydroxide and subsequent metal oxide. Additionally, the strategy developed here can be applied to multiple kinds of metal oxides. By this method, the processing temperature can be lowered by at least 50 oC and time can be shortened by half for the fabrication of perovskite photovoltaics. Significantly, the hydroxide-assisted strategy we developed here shows no specificity in terms of the type of metal. The sol-gel reaction of metal oxides ranging from NiO, Co3O4, CuO, TiO2, and In2O3 can be manipulated by this strategy, leading to reduced annealing temperature and shortened annealing time. Our results open up new paradigm to fabricate highly crystalline metal oxide thin films quickly at energy saving low temperature using solution process.

並列關鍵字

perovskite photovoltaics ； single crystals ； facet engineering ； metal oxide thin films ； low temperature fabrication

參考文獻

1. Kojima, K. Teshima, Y. Shirai, T. Miyasaka J. Am. Chem. Soc., 2009, 131, 6050-6051.

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