研究生: |
吳瑞琪 Wu, Jui-Chi |
---|---|
論文名稱: |
藉由加入界面層及熱退火處理提升有機太陽能電池效率 Improvement of Organic Solar Cell Efficiency by Adding Interlayer and Thermal Annealing |
指導教授: |
陳貞夙
Chen, Jen-Sue |
學位類別: |
碩士 Master |
系所名稱: |
工學院 - 材料科學及工程學系 Department of Materials Science and Engineering |
論文出版年: | 2010 |
畢業學年度: | 98 |
語文別: | 中文 |
論文頁數: | 121 |
中文關鍵詞: | 有機太陽能電池 、界面層 、氟化鋰 、氧化鎂 、氧化鋅 |
外文關鍵詞: | Organic solar cell, interfacial layer, LiF, MgO, ZnO |
相關次數: | 點閱:83 下載:0 |
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本研究以P3HT混合PCBM作為有機太陽能電池的主動層材料,在主動層和鋁陰極之間加入不同的界面層:LiF、MgO、ZnO。此三種界面層材料具有不同的能隙寬度以及不同的陰陽離子電負度差,基於以上性質的差異,將探討不同界面層對於太陽能電池之短路電流以及開路電壓的影響。此外,實驗在完成鍍製鋁陰極步驟後,將元件置於加熱板上進行10分鐘的熱退火處理,比較不同的熱退火溫度對P3HT:PCBM太陽能電池光電轉換效率的影響。
實驗利用原子力顯微鏡來觀察主動層上覆蓋不同界面層時的表面起伏狀況,並且經由相影像(phase image)來觀察P3HT:PCBM混合膜中成分分佈以及相分離的情況。以X光光電子能譜分析來探討各界面層添加於主動層上之後是否仍屬於該化學計量比之化合物,並觀察界面層是否和主動層材料發生反應。實驗也以紫外光-可見光光譜來觀察主動層吸光的變化情形、以拉曼光譜來量測主動層中P3HT分子鍵結共振,以及利用X光繞射分析偵測P3HT的結晶程度。太陽能電池的光電轉換效率以及各項光伏打特徵參數是利用太陽能模擬器搭配雙極性電源電表量測得到的。
實驗結果發現,添加至P3HT:PCBM主動層與鋁陰極間的界面層並不會和主動層發生反應。綜合主動層表面粗糙度的差異以及界面層因能隙寬度不同所具不同程度之電子傳輸和阻擋電洞的能力,使得添加ZnO界面層的P3HT:PCBM太陽能電池得到最高的短路電流30.24 mA/cm2,其次為添加LiF界面層時17.79 mA/cm2,再次之為添加MgO界面層時之13.57 mA/cm2,最低的短路電流值則為未添加界面層之10.63 mA/cm2。此外,由於LiF的陰陽離子電負度差極大,會在主動層和鋁陰極的界面形成強大的偶極(dipole),使得鋁的真空能階向上偏移,減少PCBM和鋁陰極之間的能障(φb)而降低電壓損失,因此添加LiF界面層元件的開路電壓相較於未添加界面層的太陽能電池增加了0.12 V。
II
添加的三種界面層材料對於P3HT:PCBM太陽能電池之填充因子數值大致相似,因此對光電轉換效率的影響乃為綜合短路電流及開路電壓之變化所得,其中:添加旋轉塗佈ZnO界面層之太陽能電池效率5.10%>添加LiF界面層之太陽能電池效率3.55%>添加MgO界面層之太陽能電池效率2.08%>未添加界面層之太陽能電池效率1.74%。
在熱退火處理方面,實驗發現經過140℃熱退火處理10分鐘、未添加界面層的P3HT:PCBM太陽能電池之主動層能達到最恰當的相分離程度,同時提高短路電流及開路電壓,故有最佳的光電轉換效率3.73%。若將添加不同界面層之太陽能電池進行140℃、10分鐘的熱退火處理,則能夠更進一步提升元件的效率:添加ZnO界面層時為6.98%、添加LiF界面層時為5.93%、添加MgO界面層時為4.61%。
Three interlayers (LiF, MgO, ZnO) are inserted between active layer and cathode of the P3HT:PCBM solar cells. Depending on their energy levels and electronegativity difference of constituent elements, these interlayers will affect the short circuit current and open circuit voltage of solar cells to different degrees. Furthermore, after depositing the aluminum cathode, some devices are subjected to thermal annealing process to gain the higher efficiency of solar cells.
Atomic force microscopy (AFM) was utilized to explore the surface roughness and phase separation of active layer via the topography and phase images, respectively. Chemical bonding states of interlayers and their interactions with the active layer were examined by X-ray photoelectron spectroscopy (XPS). The absorbance of active layer was measured by UV-Visible spectrophotometer. Raman spectrometry was carried out to detect molecular bonding resonance of P3HT. X-ray diffraction (XRD) was employed to explore the crystallization of P3HT. The cell efficiency and photovoltaic parameters were measured by solar simulator and multi-channel I-V test unit (Keithley 2400).
Combining the surface roughness of the active layer and the ability of interlayers to transport electrons or block holes from cathode, the short circuit current of P3HT:PCBM solar cells with different interlayers are showing the trend: device with ZnO interlayer (30.24 mA/cm2) > device with LiF interlayer (17.79 mA/cm2) > device with MgO interlayer (13.57 mA/cm2) > device with no interlayer (10.63 mA/cm2). Besides, owing to strong interfacial dipole moment between active layer and cathode introduced by LiF, the energy level of aluminum will be lifted upward, leading to reduction of barrier height between PCBM and Al. Thus, the device with LiF interlayer will own the largest open circuit voltage. Based on the influences on the short circuit current and open circuit voltage, efficiency of P3HT:PCBM solar cells are: 5.10% with ZnO interlayer, 3.55%
IV
with LiF interlayer, 2.08% with MgO interlayer, and 1.74% with no interlayer.
On the thermal annealing process, experiments show thermal annealing at 140 for ℃10 minutes will elevate phase separation of the active layer without interlayer, as well as increase both short circuit current and open circuit voltage, leading to an efficiency of 3.73%. When the devices with interlayers undergo thermal annealing process, their performance will improve to: 6.98% with ZnO interlayer, 5.93% with LiF interlayer, and 4.61% with MgO interlayer.
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