| Summary: | 博士 === 國立臺灣大學 === 化學研究所 === 106 === This thesis can be divided into 2 parts. The first was concentrated on designing and synthesizing donor materials for the organic photovoltaics (OPVs). The second part was focused on developing of electron transporting materials for the perovskite solar cells (PVSCs).
In the first part, we have synthesized and characterized a series of diketopyrrolopyrrole (DPP)-oligothiophene copolymers, of which the number of regioregular oligothiophene ring (2T, 3T and 4T) and the arrangement of the alkyl side-chain on regioirregular quarterthiophene (4T0, 4T1 and 4T2) are variable. The side chains with regioregular lead to more planar copolymer backbones and higher short circuit current (JSC), but backbone torsion (due to regioirregular side chains) generates greater open-circuit voltages (VOC) for DPP-oligothiophene copolymers. The increasing thiophene ring progressively raises HOMO energy level of copolymers but marginally affects their band gaps. Additionally, the HOMO energy level was found declined significantly with side-chain regioirregularity, because of reducing length of π-conjugation. The HDDPP4T0 exhibits the strongest absorption, extensive network structure, and high hole mobility (µh = 6.04 × 10-4 cm2 V-1 s-1). These characteristics contribute to the exceptional high JSC of 18.96 mA cm-2 for OPV with PCE = 6.12%. However, the HDDPP4T1 having an optimal combination of π-conjugation and energy level affords the second highest VOC (0.73 V) and the third highest JSC (16.89 mA cm-2), resulting the best PCE of 7.51 % among all. X-ray scattering, transmission electron microscopy, atomic force microscopy, and space-charge-limited-current (SCLC) easurements reveal that the solvent additive of diphenylether (DPE) enables PC71BM-blended copolymers thin film in crystallinic fibril with enhanced hole mobility.
In the second part, we have developed and demonstrated three solution processable perylene diimides, i.e., X-PDI, X = H, F, or Br, as nonfullerene electron accepting and electron transporting materials in inverted PVSCs. Whereas H-PDI or F-PDI performs
unsatisfactorily, our best PVSC is based on Br-PDI exhibiting PCE of 3.23%, which is just a bit shy of 4.13% of fullerene (PC61BM) PVSCs. Through a series of physical, spectroscopic, and microscopic studies, we have understood that the low solubility of F-PDI is a major factor causing the poor quality of the thin film, rendering virtually no photovoltaic effect for F-PDI. Although the solubility of H-PDI is better than F-PDI, the inferior electron mobility and conductivity make H-PDI PVSCs have relatively worse performance. Having the highest solubility, electron mobility, and conductivity among X-PDI, Br-PDI based PVSCs are almost as efficient as PC61BM based PVSCs. Within the ZnO NP as a CBL in the PVSCs, the PCEs of PVSCs based on X-PDI or PC61BM are significantly improved to 7.78%, 10.50%, and 11.07%, respectively.We infer that the CBL of ZnO NP has the function of interspacelling on the defect of X-PDI or PC61BM thin film, reducing the direct contact of Ag cathode to the perovskite material. Due to the strong molecular interaction, F-PDI aggregates significantly in thin film, creating too many and too large defects to be remedied or improved with or without CBL of ZnO NP. Very poor electron mobility and conductivity of F-PDI are two other factors devastating its PVSCs. Through this study, we have demonstrated that the simple mono-bromine substituted perylene diimide (Br-PDI), is solution processable and has potential for use as a non-fullerene electron accepting and electron transporting material in inverted PVSCs.
|
|---|
