溶液製程石墨烯／矽異質接面太陽電池分析

石墨烯是一擁有優良特性的二維材料，可以被運用於各種光電元件之中。然而傳統利用化學氣相沉積法 (Chemical Vapor Deposition; CVD) 於銅箔上成長石墨烯薄膜並進行轉印的做法，還是有面臨一些挑戰，像是轉印過程中聚甲基丙烯酸甲酯 (Polymethylmethacrylate; PMMA)的殘留、單原子層石墨烯的汙染或損壞等。在本論文中，我們利用簡單的溶液石墨烯製程做法來製作太陽電池，可以省去耗時的轉印步驟與可以在低溫的室溫情況下進行，做出的電池轉換效率也暫達到了5.19%可比較的程度，僅僅藉由控制溶液塗佈的參數，還可以控制石墨烯在崎嶇金字塔型矽結構上的層數堆疊情形。在製程過程中，我們利用石墨烯乙醇分散液與旋轉塗佈機，將片狀的石墨烯旋轉塗佈於選定的矽基板之上，並鍍上電極，形成異質接面電池。藉由改變各電池片的旋塗參數，進行各種特性量測，找到最佳參數。在I-V特性量測的部分，轉換效率可以達到5.19%，其它特性參數的部分，開路電壓(Open-Circuit Voltage; Voc)為0.45V; 填充因子(Fill-Factor; FF)為50.7%; 而短路電流密度(Short-Circuit Current Density; Jsc)為 23.3 mA/cm2。在結構特性上，我們有使用掃描式電子顯微鏡(Scanning Electron Microscopy; SEM)觀察平坦矽及金字塔型矽基板與其上的石墨烯; 也有進行拉曼光譜(Raman spectra)量測，觀察到石墨烯的主要譜峰G、D、2D，整個光譜顯示石墨烯成功的分佈在基板上，但是由較為微弱的2D訊號、G/2D的比值、半峰全寬等譜線特性分析，發現石墨烯的厚度會堆疊至10nm以上; 同時我們也進行了原子力顯微鏡（Atomic Force Microscope; AFM）量測，觀察到2D圖、剖面高度掃描圖及3D表面掃描圖，藉由AFM圖形觀察到石墨烯在矽上的分佈以及堆疊的高度。在此論文的實驗中，我們僅使用石墨烯分散液、矽基板為主要材料，搭配旋轉塗佈機、濺鍍機，就可以在短時間製作出有效的太陽電池。可大面積製作、價格便宜等特性也可運用在未來相關的元件發展之上。

關鍵字

石墨烯；異質接面太陽電池；特性觀察；電性量測

並列摘要

Graphene/silicon heterojunction solar cells attract intensive interest due to unique properties of graphene, simple device structure and the cost-effective process. In recent years, researchers have successfully fabricated high quality graphene using chemical vapor deposition (CVD). However, there is still some difficulty to transfer as-grown graphene onto large-area and textured substrates. The challenges include PMMA residue and damage or contamination of atomic layer graphene. Here, we report the solution-processed graphene/silicon heterojunction solar cell with a power conversion efficiency of 5.19%, which is comparable to the solar cells fabricated by transfer process. By using our proposed solution process, the device can be simply fabricated under low temperature without complex transfer procedures and the layer of graphene coated on the pyramidal silicon wafer can also be easily controlled. In the fabrication procedure, by using the graphene-dispersed ethanol solution, we are able to spin the sheets of graphene onto the top of the selected silicon substrate via spin coating method. Then, we sputter the silver on the top as electrodes of a heterojunction solar cell. We optimize the best performance of the solar cell by varying the parameters of spin-coating procedure, such as spin times and spin speed. In the current density-voltage (J-V) characteristic measurement, the power conversion efficiency of the solar cell reach the level of 5.19%, while the open circuit voltage(Voc) is 0.45V, fill factor (FF) is 50.7%, and short-circuit current density(Jsc) is 23.3 mA/cm2. To investigate the morphology of the graphene on planar and pyramidal silicon, the Scanning Electron Microscope(SEM), Raman spectra, and Atomic Force Microscope(AFM) were taken. The Raman spectra results show the main D-, G-, and 2D-peaks of graphene. The spectral results display that the graphene sheets were successfully distributed over the surface of the substrate. But according to the relatively weak 2D peak, ratio of G to 2D, and the Full Width at Half Maximum(FWHM) of 2D peak, we find that the thickness of stacked graphene sheets will be up to 10nm or more. We also conducted the AFM measurements, and observed the 2D view, section height scans, and 3D surface scans. In this experiment, we use only graphene-dispersed solution and silicon substrate as the main materials to produce an effective solar cell in a short time. Large-area, low-temperature, and costly can also be great advantages in the future works on the development of related optical devices.

並列關鍵字

Graphene ； Heterojunction solar cells ； Characterization ； Electrical properties

參考文獻

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溶液製程石墨烯／矽異質接面太陽電池分析

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