| Summary: | 博士 === 國立成功大學 === 光電科學與工程學系 === 102 === This thesis is divided into two part: firstly, we investigated the roles of poly(ethylene oxide) polymer been used as an effective buffer with Al electrode to markedly improve the electrode interface and enhance the open-circuit voltage (VOC) and the power conversion efficiency (PCE) of poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61-butyric acid methyl ester (PCBM)-based bulk-heterojunction (BHJ) solar cells. A unique process by thermally co-evaporating the poly(ethylene glycol) dimethyl ether (PEGDE, Mn ca. 2,000) polymer with Al metal simultaneously at different ratios in vacuum (10-6 torr) was developed to prepare the electrode buffers. The VOC and PCE for devices fabricated with Al electrode are 0.44V and 1.64%, respectively, and largely improved to 0.58V and 4.00% applying PEGDE:Al (2:1)/Al electrode under standard 1 Sun AM 1.5 simulated solar irradiation.
Secondly, we fabricated methylammonium lead iodide (CH3NH3PbI3)/fullerene (C60), donor/acceptor planar-heterojunction (PHJ) solar cells. The deposition of a thin C60 (acceptor) layer in vacuum on CH3NH3PbI3 perovskite (donor) creates a hybrid PHJ for fabricating solar cells. CH3NH3PbI3 perovskite harvests the wild range of light from visible-to-near infrared and transports the positive charges. The CH3NH3PbI3/C60 PHJ devices exhibits the promising photovoltaic performance. In addition, the magnitudes of VOC and PCE elevate to 0.65 and 0.75 V, 2.4 % and 2.1 % using PCBM and indene-C60 bisadduc (ICBA), respectively, of higher lowest unoccupied molecular orbital (LUMO) level, instead of C60 as the acceptor. These results verify the functions of CH3NH3PbI3 perovskite/C60 or C60 derivatives PHJ to the modulation of the photovoltaic parameters and the development of newly designed, hybrid, efficient solar cells. We also find the difference between the highest occupied molecular orbital (HOMO) level of CH3NH3PbI3 perovskite and the Fermi level of ITO dominates the voltage output of the device. With ITO films on glass or on the polyethylene terephthalate (PET) flexible substrate with different work functions, we show significant VOC enhancement (920mV).
Applying a thin nickel-oxide (NiOx) interlayer between glass/ indium-tin-oxide (ITO) electrode and light absorbing CH3NH3PbI3 perovskite significantly increases the photovoltaic performance of perovskite/fullerene-derivative PHJ solar cells. First, NiOx electrode-interlayer is a p-type semiconductor of high work function of 5.4 eV, which is close to the valence band edge level of CH3NH3PbI3 perovskite (5.4 eV). The alignment of energy level minimizes the interfacial energy losses for the hole transfer and optimizes the photovoltage output of device. Second, CH3NH3PbI3 perovskite films prepared by the spin-coating process on glass/ITO/NiOx substrate exhibit a relatively smooth morphology than those deposited on glass/ITO/ PEDOT:PSS substrate. The conformal coverage of the perovskite film enhances the light harvesting, reduces the leakage current, increases JSC, and elevates the PCE of the devices. The best performing cell with the configuration of glass/ITO/NiOx/CH3NH3PbI3 perovskite/PCBM/bathocuproine/Al presents a VOC = 0.92 V, a JSC = 12.43 mA/cm2, and a FF = 0.68, corresponding to a PCE of 7.8 %.
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