第三章 結果與討論
3.8 電荷深層能階瞬間光譜儀(Q-DLTS)研究
為了進一步探討CdSe/ZnS量子點在元件中的特性，我們使用Q-DLTS 儀器來研究元件中的電荷陷域，其計算理論在第二章已介紹過。Fig. 3-27 為元件ITO/PEDOT/MEH-PPV/Al在施加電壓為△V= + 1V不同充電時間下 的Q-DLTS圖譜，隨著充電時間的增加，釋放出來的電荷有趨於飽和的趨 勢。利用公式可將圖譜分解成四個不同的波峰，分別標示為Peak I、Peak II、Peak III和Peak IV，分解的圖譜顯示於Fig. 3-28，四個不同的波峰即表 示至少有四個不同的陷域(trap)存在於元件中，接著利用在不同溫度下所紀 錄的Q-DLTS圖譜，如Fig. 3-29 所示，即可計算出每一個陷域的參數，每 一個陷域隨著溫度改變而位移的圖譜分別列於Fig. 3-30、3-31 和 3-32，利 用第二章的公式( 3 )，從-ln (τT2) v.s. 1/KT圖譜的斜率和截距可以得到活化 能EA和陷域交錯區域σ，Peak I、Peak II和Peak III每一個陷域的arrhenius圖 形則分別表示於Fig. 3-33、3-34 和 3-35，陷域密度NT則是利用每個波峰的
為摻混濃度 0.4 % CdSe/ZnS 量子點元件的 Peak V 波峰隨著溫度變化的圖 形和此陷域的 arrhenius 圖形。兩個不同摻混濃度元件的每一個陷域參數結 果整理並列於 Table 3-6。CdSe/ZnS 量子點經過計算的陷域活化能大約介 於 0.1~0.15 eV，和之前的研究比較，相似的奈米粒子活化能可以被觀察到
Fig. 3-27. Q-DLTS spectra measured on a ITO/PEDOT:PSS/MEH-PPV/ Al device using an offset V0 = 0V, a charging voltage ΔV = + 1V for different charging time from 1 ms to 1 s at T=300 K.
0
Fig. 3-28. Decomposition of the Q-DLTS spectra recorded in MEH-PPV diode at 300 K obtained with a charging time tc = 1 s and a charging voltage ΔV = + 1
Fig. 3-29. Q-DLTS spectra measured on a ITO/PEDOT:PSS/MEH-PPV/Al device using a charging voltage ΔV = + 1V and charge time time tc = 1 s for different temperature from T=270-320 K.
0
Fig. 3-30. Peak I obtained from the Q-DLTS spectra recorded in a ITO/
PEDOT:PSS/MEH-PPV/Al diode for different temperatures in the range 270 - 320 K with a charging time tc = 1 s, a charging voltage: ΔV = + 1 V.
Fig. 3-31. Peak II obtained from the Q-DLTS spectra recorded in a ITO
/PEDOT:PSS/MEH-PPV/Al diode for different temperatures in the range 270 - 320 K with a charging time tc = 1 s, a charging voltage: ΔV = + 1 V.
0
Fig. 3-32. Peak III obtained from the Q-DLTS spectra recorded in a ITO
/PEDOT:PSS/MEH-PPV/Al diode for different temperatures in the range 270 - 320 K with a charging time tc = 1 s, a charging voltage: ΔV = + 1 V.
Fig. 3-33. Arrhenius curve for Peak I of the ITO/PEDOT:PSS/MEH-PPV/Al device.
-7,4 -7,2 -7 -6,8 -6,6 -6,4 -6,2
36 36,5 37 37,5 38 38,5 39 39,5 40 1/kT (eV
-1)
-ln( τT
2)
Fig. 3-34. Arrhenius curve for Peak II of the ITO/PEDOT:PSS/MEH-PPV/Al device.
-10,5 -10 -9,5 -9 -8,5
36 37 38 39 40 41 42
1/kT (eV
-1) -l n (τ T
2)
Fig. 3-35. Arrhenius curve for Peak III of the ITO/PEDOT:PSS/MEH-PPV/Al device.
0
Fig. 3-36. Q-DLTS spectra measured on a ITO/PEDOT:PSS/MEH-PPV + 0.2 % QD/Al device using a charging voltage ΔV = + 1V and charge time time tc = 1 s for different temperature from T=270-320 K.
0
Fig. 3-37. Decomposition of the Q-DLTS spectra recorded in MEH-PPV+0.2%
QD diode at 300 K obtained with a charging time tc = 1 s and a charging voltage ΔV = + 1V.
0 50 100 150 200 250 300
1 2 3 4 5 6 7
Δ Q (p C )
log(τ) (τ: us)
270 K 320 K
Fig. 3-38. Peak V obtained from the Q-DLTS spectra recorded in a ITO / PEDOT:PSS/MEH-PPV+0.2%QD/Al diode for different temperatures in the range 270 - 320 K with a charging time tc = 1 s, a charging voltage: ΔV = + 1V.
-11 -10,9 -10,8 -10,7
36 37 38 39
1/kT (eV
-1) -l n (τ T
2)
Fig. 3-39. Arrhenius curve for Peak V of the ITO/PEDOT:PSS/MEH-PPV + 0.2
%QD/Al device.
0
Fig. 3-40. Q-DLTS spectra measured on a ITO/PEDOT:PSS/MEH-PPV + 0.4 % QD/Al device using a charging voltage ΔV = + 1V and charge time time tc = 1 s for different temperature from T=270-320 K.
0
Fig. 3-41. Decomposition of the Q-DLTS spectra recorded in MEH-PPV+0.4%
QD diode at 300 K obtained with a charging time tc = 1 s and a charging voltage ΔV = + 1V.
0 100 200
0 1 2 3 4 5 6 7
Δ Q (pC )
log(τ) (τ: us) 320K
270K
Fig. 3-42. Peak V obtained from the Q-DLTS spectra recorded in a ITO/
PEDOT:PSS/MEH-PPV+0.4%QD/Al diode for different temperatures in the range 270 - 320 K with a charging time tc = 1 s, a charging voltage: ΔV = + 1V.
-11.2 -11 -10.8 -10.6
36 37 38 39
1/kT (eV
-1) -l n( τT
2)
Fig. 3-43. Arrhenius curve for Peak V of the ITO/PEDOT:PSS/MEH-PPV + 0.4
%QD/Al device.
0
Fig. 3-44.Comparision of Q-DLTS spectra recorded in pure MEH-PPV and adding 0.2% and 0.4% QD diodes at 300 K with a charging time tc = 1 s, a charging voltage: ΔV = + 1V.
Table. 3-6. Summary of the trap parameters in ITO/PEDOT/MEH-PPV+ (CdSe/ZnS) / Al devices.
Sample name trap