Theoretical Calculations For A Series Of Polymer Photoelectric Materials

The organic optoelectronic materials have been extensively used in the filed of organic photovoltaic cells, light emitting diodes, organic field-effect transistors, and organic sensors. Polymer photovoltaic cells (PSCs) have attracted attentions due to their potential low cost, light weight, flexibility, and easy manufacturing. In the past decade, the power conversion effect (PCE) has reached8.3%. However, the low PCE is still an obstacle to their commercialization. The quantum chemical calculations not only can explain the photoelectric conversion mechanism of PSC, but also can predict new polymers with excellent photovoltaic performance. This thesis is aimed at the subject, and systematically and detailedly studies a series of polymers for PSC. The studies include the photoelectric conversion mechanism and design of benzodithiophene-like polymers, the photovoltaic performance prediction of pyridazine-like polymers, and the potential study of the furofuran polymers for solar cells. In addition, after nearly two decades of research and development, the polymer light-emitting diodes (PLEDs) have been the targets of some researchers due to their wide viewing angle, low drive voltage, large area display, self-luminance, high-resolution, fast response, and simple process. At present, high performance blue, green, red, and white light-emitting polymers are required to realize PLED-based displays, whereas only a few blue light-emitting polymers show good performance in comparison with other light-emitting polymers. In the thesis, the photophysical properties of five blue light-emitting polymers based on spirobifluorene applied in PLED materials have been studied by quantum chemistry.Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations have been employed to model PBDTTBT to rationalize the relationship between the experimentally observed properties and the structural features in PSC. Besides, according to PBDTTBT, we designed four benzodithiophene-like copolymers, PBDTTTP, PBDTTTO, PBDTTTPD, and PBDTTFPD. In order to investigate their potentials as donors in PSC based on PC70BM, several parameters of determining the performance of solar cells, stability, open-circuit voltage, and short-circuit current, have been researched through analyzing their structure and properties stability, abilities of harvesting influx photons from the sun, abilities of exciton generation and separation, carrier injection ability, and hole mobility. Comparing the four designed copolymers with PBDTTBT, we conclude that PBDTTTP and PBDTTTO have more favorable photovoltaic properties due to their better structure and properties stability, more easily harvest the maximum of the photon flux from the sun, lower bandgaps, deeper HOMO levels, and larger hole mobility. Consequently, PBDTTTP and PBDTTTO are promising candidates for polymer BHJ solar cells.Based on pyridazine,[1,2,5]thiadiazolo[3,4-d] pyridazine,[1,2,5]oxadiazole[3,4-d]pyridazine, isothiazolo[3,4-d]pyridazine, and isoxazolo[3,4-d]pyridazine, fifteen polymers have been theoretically studied to test their potential as donors for PSC. Those polymers contained five homopolymers (PP, PTP, POP, PITP, and PIXP) and ten copolymers (PTHP, PTHTP, PTHOP, PTHITP, PTHIXP, PDTHP, PDTHTP, PDTHOP, PDTHITP, PDTHEXP). Herein, the copolymers were composed of the above five compounds and thiophene incorporated with1:1and1:2ratios. The fifteen polymers have been examined in terms of the open-circuit voltage, band gap, absorption spectra, hole transport property, and short-circuit current. The results indicate that the incorporation of thiophene greatly improves the photovoltaic performance of polymer/PC61BM cells. Especially PDTHTP, PDTHOP,PDTHITP, and PDTHIXP are champion materials for donors in designed polymer solar cells.Four copolymers (PBTP, PBOP, PBTPD,and PBFPD) based on benzodithiophene and pyridazine derivatives were presented to study their potentials as donors in polymer bulk-heterojunction solar cell based on PC61BM. Several parameters of determining the performance of solar cells, the abilities of absorbing sunlight, structure and properties stability, and photovoltaic properties have been studied in terms of analyzing their absorption spectra, antioxidation property, photo stability, abilities of exciton generation and dissociation, carrier injection ability, hole mobility, and open-circuit voltage by employing density functional theory. The results indicate that all the copolymers are favorable candidates for polymer solar cells, especially PBTP and PBOP.The structural, electronic, and optical properties of poly(3-hexylthiophene)(P3HT) have been comprehensively studied by density functional theory (DFT) to rationalize the experimentally observed properties. Rather, we employed periodic boundary conditions (PBC) method to simulate the polymer block, and used Marcus theory for describing charge transport properties. The simulated results of P3HT are consistent with the experiment in band gaps, absorption spectra, and hole mobilities. Based on the same calculated methods as well as P3HT, a series of polymers have been designed on the basis of the two types of building blocks, furofurans and furofurans substituted with cyano (CN) groups, to investigate suitable polymers toward polymer solar cell (PSC) materials. The calculated results reveal that the polymers substituted with CN groups have good structural stability, low-lying FMO energy levels, wide absorption spectra, large charge-transfer rates, and small hopping barriers, which are due to their good rigidity and conjugation relative to P3HT. Besides, the insertion of CN groups improves the performance of PSC due to decreasing band gaps and hopping energy barriers, improving structure and properties stability, enhancing carrier mobilities, and broadening the absorption spectra in visible region. Synthetically considering the properties of affecting PSC, we conclude that PFF3a and PFF3b in the designed polymers are the champion candidates toward PSC relative to P3HT.The photophysical properties of five blue light-emitting polymers based on spirobifluorene applied in polymer light-emitting diodes (PLED) materials have been studied by quantum chemistry. In order to understand the intrinsic reasons for the different performances displayed by the polymers, we carried out density functional theory (DFT) and Marcus theory investigations on their oligomers in terms of structure and properties stability, absorption and emission properties, and carrier injection and transport properties. Especially, some important parameters which had not been reported to our knowledge were given in this contribution, such as the ionization potentials (IPs), electron affinities (EAs), reorganization energies (λ), ke/kh (the ratio between the electron transfer rate (ke) and hole transfer rate (kh)), and the radiative lifetimes (τ). The main results indicate that the co-oligomers of PCC-1, PCC-2, and PCC-3with push-pull interactions produced by the existing D-A segments have better carrier injection and transport properties than the oligomers of PSF and PCF. Especially PCC-2co-oligomer, its large radiation lifetime (7.46ns) and well balanced and adequate carrier transport guarantee its champion performance for PLED. The calculated results coincide with the experimental ones. Besides, PNF of structurally similar to PCC-2has similar photoelectric properties to PCC-2in theory, and the fluorescence emission of PNF co-oligomer is superior to PCC-2co-oligomer. Therefore, we predict that PNF is a promising candidate for PLED.