水溶液製程之薄矽與砷化鎵基混合式太陽能電池

Abstract

矽基與砷化鎵基的太陽能電池的轉換效率遠高於以其他材料為主的元件，製程技術 也非常成熟，惟其發電成本過高，無法取代石油、煤氣為主的民生用電，然而隨著矽晶 片和砷化鎵晶片減薄技術的純熟，可望大幅降低晶片型太陽能電池的成本，已成為產業 的未來趨勢，然而這兩種元件的傳統製程方式，仍需要使用高耗能、高真空的設備，導 致製程成本仍居高不下，因此在本計晝中，我們提出以水溶液製程為主的混合式太陽能 電池，搭配薄矽或砷化鎵薄膜來大幅降低發電成本。利用寬能隙有機材料與矽或砷化鎵 晶片間形成的異質接面，或石墨烯-矽形成的蕭特基接面，可以有效分離載子，理論效 率可以達到20°%。而本實驗已發展出轉換效率10%的元件，其製程僅使用旋塗、熱蒸鍍金 屬等低耗能步驟，於室溫、一大氣壓等自然條件下完成，因此極有潛力成為下一代低成 本高效率太陽能電池的主流。

我們的研究預計有三個主要方向，分別為（a)高效率矽基混合型太陽能電池、（b) 薄膜化砷化鎵混合型太陽能電池、（c)石墨烯蕭特基接面混合型太陽能電池。在這三種 混合式太陽能電池的結構下，發展高效率低成本的製程，在（a)部分因矽基混合式太陽 能電池目前已可達到10°%的轉換效率，實驗室將著重於發展全水溶液製程，包括旋塗之 奈米線透明導電電極、背表面場以及表面鈍化技術，持續提高元件效率，期能達到15°% 以上的轉換效率。在(b)的部分，砷化鎵基混合式太陽能電池在實驗室仍屬於新穎課題。 因為砷化鎵的能隙較矽高，會有較大的開路電壓，而最新砷化鎵太陽能電池的進展（最 高效率28.8°%)又提出光學設計，開路電壓又與晶片息息相關，因此我們透過晶片減薄及 利用表面光子晶體的製作可以調變出光角，此計晝與英國南安普敦大學合作，以驗證太 陽能電池轉換效率的重要理論。在（c)的部分，石墨烯在目前研究已可大面積製造，用 於顯示器等工業產品的透明導電電極，因此利用石墨烯與矽結合的蕭特基接面太陽能電 池也極有潛力成為低成本的太陽能電池量產技術，然而要提高元件效率，石墨烯的摻雜 與導電性的提升是重要的課題，我們將發展水溶液製程的摻雜技術與摻混導電奈米線等 方式提高石墨烯-矽的混合式太陽能電池的元件效率。

總而言之，藉由本實驗室在過去4年建立的太陽能電池關鍵製程與量測技術，此計 晝所研發出的成果與專利技術可望提昇國際學術聲望與國家產業界的競爭力。此外本計 晝所培育的太陽能電池專業人才將有助於國内太陽能產業的技術以及研發能力的增進。

Silicon- and GaAs-based solar cells have the highest power conversion efficiencies among the available photovoltaic technologies. However, the electricity cost is still too high compared to that of fossil fuels, which limits the terrestrial applications. With the mature of wafer-thinning techniques, one can expect a price drop of wafer-based solar cells in the near future. Nevertheless, the fabrication cost, typically 25-30% of the total cost, is still significant due the essentialness of energy intensive processing procedures and equipment. Therefore, in this proposal, we introduce solution-processed approaches to fabricate high-efficiency hybrid silicon- and GaAs-based solar cells. In this frame work, we employ either highly-conductive organic materials or Graphene to form hetero- or Schottky- junction with Si or GaAs thin films. The power conversion efficiency is currently around 10%, demonstrated by us and other groups. However, the projected efficiency can be as high as 20% by means of better light management, interface defect control, and doping of the p-type organic materials and Graphene.

We propose to investigate three different material systems and device architectures, namely (a) High-efficiency organic-silicon heterojunction solar cells (b) Thin-film organic-GaAs hybrid solar cells, and (c) Graphene-silicon Shottky-junction solar cells. In topic (a), we will focus on all-solution approaches to achieve high-efficiency devices, including front and back surface passivation, back surface field, and transparent nanowire electrode by spin-coating. In (b), the concept of GaAs hybrid solar cells is fairly new. However, the recent record efficiency of GaAs solar cells (”=28.8%) suggest that the open-circuit voltage is highly related to light-management of the device. Therefore, we will collaborate with Dr. Martin Charlton, and Prof. Darren Bagnall to investigate the impact of light extraction from photonic and quasi-photonic crystals on the photovoltaic characteristics. Finally, in (c) we believe that the Graphene-silicon hybrid cells is very competitive to other technologies due the capability of large-scale production of graphene for the transparent electrode in displays. To increase the efficiency, we will investigate various approaches such as organic or nanowire doping to boost the conductivity of graphene.

In summary, the proposed approaches are rooted on our experience in solar cell development for the past six years. We are very capable of realizing the objectives set in this project due to well-established device fabrication and characterization systems in our laboratory at National Chiao Tung University. The technical trainings of graduated students and intellectual properties generated during executing the project will add invaluable contributions to industry in Taiwan.