| Summary: | 碩士 === 國立中山大學 === 光電工程學系研究所 === 104 === In this study, the sol–gel method was employed to prepare a ZnO thin film as cathode buffer layer in inverted organic solar cells (IOSCs). We demonstrated a low temperature sol-gel process by adjusting the molar ratio of zinc acetate dihydrate (ZAD) to monoethanolamine (MEA), and successfully fabricated the inverted solar cells on flexible plastic substrate.
The zinc oxide (ZnO) sol-gel was made by dissolving ZAD and MEA in ethylene glycol monomethyl ether (EGME). The molar ratio of ZAD to MEA were set at 1:1.2, 1:1, and 1:0.8. We investigated the different characteristics of the ZnO thin films. Power conversion efficiency was enhanced when the annealing temperature of ZnO was lowered to 125℃ by using the ratio of 1:1 and 1:0.8.
In this research, we investigated the optical transmittance, surface roughness and surface morphology. Then, we discussed the reasons about the improvement of the device efficiency. The devices were fabricated using the ZnO thin films for cathode buffer layer. The structure of inverted device is ITO/ ZnO/ P3HT:PCBM/ MoO3/ Ag.
The result indicated that the thin films’ morphology made by the sol-gel in the ratio of 1:1 and 1:0.8 transferred to ripple nanostructure after two times annealing. Power conversion efficiency was enhanced because of the more light absorption in the active layer caused by the nanostructure. The short circuit current (8.59 mA/cm2 and 8.34 mA/cm2, respectively) was higher than the device with ZnO thin film which was annealed at 150℃. Inverted solar cells with 125℃ annealing temperature exhibited PCEs of 3.38% and 3.30% respectively. More than that, PCEs of the flexible device can reach up to 1.26%.
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