本論文主要是研究石墨烯的阻障效果並嘗試應用在銅銦鎵硒(CIGS)太陽能電池中的背電極與吸收層間。在製作CIGS太陽能電池的CIGS吸收層時，Mo背電極在硒化過程中，一部份Mo容易被硒化成MoSe2的化合物，此化合物形成在CIGS層與Mo介面間，此MoSe2化合物有助於電池Mo背電極之歐姆接觸。但是，因為MoSe2的電阻值遠高過Mo，所以當MoSe2過厚時便會造成太陽能電池的串聯電阻過大，因此出現太陽能電池效率不佳的情況。
在銅/石墨烯試片經過低溫200oC硒化後，我們發現試片之顏色仍是銅的顏色，然而，沒有石墨烯覆蓋之銅試片其顏色呈現黑色，此黑色物質證明是銅硒化合物，此實驗代表著:石墨烯可以阻障硒氣進入與底下的銅薄膜反應。但是在550℃硒化狀況下，我們發現:即便Mo上覆蓋了轉移之石墨烯，仍然會生成MoSe2，但是與Mo層沒有石墨烯的試片相比，覆蓋有石墨烯的試片仍然具有某種程度的延緩硒化的能力。經過多次石墨烯轉移之Mo試片，其XRD圖仍然出現明顯的MoSe2訊號，藉此我們推測:高溫550oC下，硒氣壓力極大(壓力是200oC時的一萬倍以上)，硒氣應該是穿過石墨烯的晶粒(grain)晶界或缺陷，或是原本生長的石墨烯時不均勻產生之破洞，而這些狀況都可以導致硒氣體穿過石墨烯層，因而Mo被硒化了。
我們進行了多種實驗，初步驗證了多晶的石墨烯有阻障硒氣的能力，但是石墨烯的晶粒晶界、破洞或缺陷限制了石墨烯阻障硒氣的能力，將來可以使用單晶石墨烯做更進一步的實驗。

The thesis primarily investigates graphene’s capability as a barrier to block selenium diffusion for the application at the interface between absorber and back-electrode in CuInGaSe2 (CIGS) solar cells. During the selenization process to form the CIGS absorber film, a portion of the Mo electrode will be selenized to MoSe2, which film is located in between the Mo and CIGS layers. The Mo/CIGS interface become a ohmic contact when a MoSe2 layer exist. However, MoSe2 film is a highly resistive film and will results in a higher series resistance and degrade the conversion efficiency of the solar cells.
We discovered that the post 200oC selenized Cu sample did not change its color when the Cu film was covered with an as-grown graphene film. In contrast, Cu sample changed to black color if Cu surface didn’t have a graphene layer on top. This black film is copper selenium compounds. The results indicate that the graphene layer is capable of blocking Se and prevent Se reacts with the underneath Cu film. As we raised the selenization temperature to 550oC using Mo samples. XRD results show that there is a MoSe2 peak for all samples, includes the sample with a multiple-transferred graphene film on top of the Mo electrode, but its degree of Mo being selenized is much less than the sample without a graphene blocking layer. For our best knowledge, the vapor pressure of selenium is at least four-order of magnitude higher than that at 200oC (~10-3 torr), Se gas must pass through graphene grain boundaries, pin holes, or defects, such that it can selenized thin Mo film.
In summary, we have done several preliminary experiments to show that a polycrystalline graphene film has some degree Se-blocking capability. Graphene grain boundaries, pin holes or defects are the main reasons that limit its blocking capability. Further studies using single crystalline graphene layer is needed.

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