| Summary: | 博士 === 國立成功大學 === 化學工程學系 === 104 === In this dissertation, three interfacial modification strategies of energy level alignment, balance charge transporting, and smooth surface morphology were applied on perovskite solar cells (PVSCs) and polymer light-emitting diodes (PLEDs) for achieving high efficiency. In the organic optoelectronic devices, three problems reduce the device performance, injection/extraction barrier energy from the mismatch with work function of electrode and energy level of organic semiconductors, recombination from the carrier accumulation in solar cells, and leakage current from the incomplete coverage of interfacial layer. Here, three strategies were applied for solving above problems for enhancing device performance.
In the first part, energy level alignment by interfacial dipole was applied for enhancing the hole injection and extraction. The hydrophilic ammonium bromide (NH4Br) with ammonium group was spun-cast atop the ITO to increase its work function via interfacial dipole. The hydrogen binding formation between ITO and NH4Br by the XPS spectra build the interfacial dipole with the direction toward ITO to lower down the vacuum level of ITO and enhance the hole injection. With that successful results, the methyl ammonium iodide part in CH3NH3PbI3 might create hydrogen bonding with ITO. Hence, perovskite thin film was prepared directly atop ITO electrode via solvent washing process to achieve 11.02 % of power conversion efficiency (PCE). The high efficiency results from the enhancement of ITO work function and hydrogen boning formation to increase the Voc to 1.01 V.
In the second part, balance charge transporting was applied via increasing the conductivity of PEDOT:PSS and blocking hole from tetraoctylammonium bromide (TOAB) respectively for PVSCs and PLEDs. The imbalance carrier transporting will cause charge accumulation at the interface to create recombination loss. PEDOT:PSS, which is the common hole transporting layer, was treated via CuBr2 to reduce its resistivity from 115.6 to 0.082 Ω.cm. The reduction of resistivity results in the 1.11 times enhancement of Jsc with the best PCE of 14.59%. The 1.86 times enhancement of Jsc from CuBr2 treated low conductivity of PEDOT:PSS, indicating the enhancement of Jsc from the carrier balance transporting. The results of XPS reveal the conductivity enhancement of PEDOT:PSS from the insulating PSS removal from the increase in the ratio between PEDOT and PSS. In PLED, most luminescence layers are p-type semiconductors. To enhance the exciton formation, sufficient hole blocking is important. Accordingly, TOAB was applied as electron injection layer (EIL) for enhancing device the performance. Three luminescence layers, G-PF, SY-PPV, and P3HT with various energy levels were used to investigate the hole blocking ability of TOAB. Compared with Ca based devices, TOAB based PLEDs shows higher current efficiency due to its hole blocking ability. Investigating the current ratio of Al and TOAB/Al devices, the hole blocking ability of TOAB increase with the decrease in the hole injection barriers. The P3HT-based device shows highest light intensity (401 cd m-2) due to sufficient hole blocking capability to form exciton.
In the third part, smooth surface morphology was applied via blending three EILs including polyethylenimine ethoxylated (PEIE), poly (vinylpyrrolidone) (PVP), and tetraoctylammonium bromide (TOAB). The AFM images show that TOAB significantly reduces the roughness of the aggregated PEIE:PVP film. It is corroborated from XPS results that the additional hydrogen bonding formed from the interaction between PEIE and PVP, being reduced with the addition of TOAB into the thin film. Accordingly, Ternary device respectively shows 1.12 and 1.09 times the current efficiency and the power efficiency of PEIE device (11.24 cd m-2 and 10.69 lm W-1), which is higher than that of in the PEIE:PVP (Binary) device (11.96 cd m-2 and 10.14 lm W-1).
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