混合型太陽能電池

混合型太陽能電池種類繁多，在此針對有機物與矽晶與砷化鎵介 面做探討，異質接面的電池在早期就有相關的研究[10，11]，結合有 機材料的便宜性和矽晶製程技術成熟， 混合兩種的優點，就是混合 型太陽能電池的優點，現在許多新型的電子元件被發表在文獻中，例 如生物感測器[12]及氣體偵測器[13]和太陽能電池[14-18]。

矽晶異質接面太陽能電池

混合型異質接面太陽能電池，見圖 2-13，主要是由有機物與矽 晶形成一寬能隙異質接面，類似於 HIT(Heterojunction with

intrinsic thinlayer)結構之太陽能電池[19]，用一寬能隙材料作為 電子或電洞阻擋層。目前已達到大面積尺寸矽晶太陽能效率最高紀 錄:24.7%[20]，超越同質矽的單晶矽太陽能電池。在結構中，寬能帶 材料是非晶矽，作為電子或電洞阻擋層，若以有機半導體材料取代非 晶矽，作為電子或電洞阻擋層，利用有機物降低製程的複雜度與製造

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1990 就有研究團隊以 poly-(CH³)³Si-Cyclooctatetraene 與 n-type 矽結合[24]此類太陽電池種類眾多，目前有多種有機材料被應用於與

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當作 n－type 矽晶中的電子阻擋層。PEDOT 是導電高分子材料，具有 較好的化學性質、熱穩定性。許多太陽能電池的研究是以 PEDOT：PSS

／n－type Silicon 為異質接面的太陽能電池，且效率可高達 9%以上 [32-35]。關於 PEDOT：PSS 導電度的提升[36-38]，我們選用 PSS 與 PEDOT 之比例為 1：2.5，這樣比例的導電度用在目前太陽能電池是最 好的。

砷化鎵異質接面太陽能電池

IBM在1972年製作異質接面GaAs太陽能電池[40，41，42]，利用液 相磊晶法成功地長出異質接面的砷化鎵太陽能電池， 隨後有研究團 隊用MOCVD 精準的控制摻雜濃度製作出更高效率的電池，利用在射極 層（emitter layer）長視窗層，使效率大幅提升。

砷化鎵異質接面太陽能電池主要是由有機溶液與砷化鎵晶圓組 成的，能帶圖如圖2-15。近幾年，許多砷化鎵混合型太陽能電池是由 PEDOT：PSS／n－type GaAs組成，有些團隊用GaAs nanowire 去做蝕 刻，在將有機溶液用旋轉塗佈或是浸泡的方法附著上去，但效率都不 高，轉換效率在6%左右[43,44,45,46]。砷化鎵可提供比較大的開路 電壓，但效率不高的原因則是因為電流密度偏低，若能改善，才能大

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有可為。

砷化鎵這種材料本身也無法在半導體表面形成穩定的氧化物，需 要藉著成長合適的磊晶結構來改善表面復合速率過高的問題， 表面 復合速率過高也進而影響短波長的外部量子轉換效率，有三個解決辦 法，其一將半導體材料表面鈍化（passivation），其二為成長具有 較高濃度的正面表面電場層(front surface field, FSF)，其原理與 矽太陽能電池的背面表面電場(back surface field, BSF)相似[47]。

其三則為具有較大能隙的窗口層(window layer)，可以反射少數載子 遠離表面，並且可以讓大部分的光通過不影響下方電池對光的吸收 量。

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表 2-1 各種太陽能光譜的量測標準

圖 2-1 太陽光光譜

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圖 2-2 太陽輻射的光譜

圖 2.3 AM 值定義

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圖 2-4 太陽能電池構造圖

圖 2-5 p-n 接面示意圖

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圖 2-6 光電流機制

圖 2-7 P-N JUCTION

(a)在接面處 p 或 n 型半導體的多數載子擴散進入 n 或 p 型半 導體；

(b)原先在半導體靠近「接面區」的載子與來自另一區半導體的載子 發生複合的現象。最後，留下帶電的施體與受體離子。

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圖 2-8 照光的理想太陽能電池等效電路

圖 2-9 照光的實際太陽能電池等效電路

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圖 2-10 照光下，太陽能電池的 IV 圖

圖 2-11 I-V 量測結果示意圖

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圖 2-12 太陽能等效電路

圖 2-13 (a)HIT 結構之太陽能電池 (b)理想的能帶校準(Band Alignment)

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圖 2-14 太陽能電池能帶圖

(a)傳統 n⁺-p-p⁺太陽能電池之能帶 (b)以適當調控能階之有機物作 為電子電洞阻擋層的混合型太陽能電池能帶圖

圖 2-15 GaAs 和 PEDOT:PSS 能階示意圖

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