Review of electronic and optical properties of semiconducting π‐conjugated polymers: applications in optoelectronics

Abstract

A general overview of the optoelectronic properties of π -conjugated polymers is presented. Two types of polymer are discerned: interchangeable structures of the same energy (degenerate), such as polyacetylene; and non-degenerate polymers, such as poly(para-phenylene). The band structures of degenerate and non-degenerate polymers are related to their conductivities in doped and non-doped states. In both cases, disorder and impurities play an important role in conductivity. Polarons, bipolarons and excitons are detailed with respect to doping and charge transfers. Given the fibrillic nature of these materials, the variable range hopping (VRH) law for semiconducting polymers is modified to account for metallic behaviours. Optoelectronic properties-electroluminescence and photovoltaic activity-are explained in terms of HOMO and LUMO bands, polaron-exciton and charge movement over one or more molecules. The properties of H-or J-type aggregates and their effects on transitions are related to target applications. Device structures of polymer light-emitting diodes are explicitly linked to optimising polaron recombinations and overall quantum efficiencies. The particularly promising use of π -conjugated polymers in photovoltaic devices is discussed.

Block copolymer strategies for solar cell technology

“…Improvements relative to PCBM, 77 which has been exceptionally successful as a processable acceptor since its inception, have been made. However, such progress has been at a slower pace than the aforementioned low band-gap polymers, perhaps due to the inherent tendency of polymers to prefer hole conduction 28 and the difficulties of working with weakly soluble fullerenes. 78 Phenyl-C 71 -butyric acid methyl ester (PC 71 BM) has proved useful 79 due to its increased light absorption at higher wavelengths with respect to PC 61 BM.…”

“…OPVs, on the other hand, have higher exciton binding energies and, therefore, excitons must reach a material interface with a lowest unoccupied molecular orbital (LUMO) offset to produce separated electrons and holes. 21 The photovoltaic mechanism in organic devices has been discussed at length in the literature, 19,[22][23][24][25][26][27][28][29] therefore, here, we only briefly outline the process for readers new to the field. Figure 1 shows the individual steps involved in the dominant process that converts light into an electrical current: (i) the incoming photon excites an electron from the HOMO to the LUMO of the donor material to (ii) create an exciton, (iii) which traverses the donor material to a donor-acceptor interface where (iv) the excited electron separates from its bound hole onto the LUMO of the acceptor.…”

Photoluminescent energy transfer from poly(phenyleneethynylene)s to near‐infrared emitting fluorophores

“…The highly efficient energy transfer 1 and exciton migration processes 2 in conjugated polymers can be exploited in various electronic applications [3][4][5][6][7][8][9][10][11] and in amplifying sensor responses. [12][13][14][15][16][17][18][19] Highly sensitive, amplified quenching of polymer emission has been accomplished with various quenchers in solution as well as in the solid state.…”

Effect of Imidazole and Surfactant on the Opto-Electrical Properties of PEDOT Thin Films via Vapor Phase Polymerization

“…[3][4][5] By virtue of their potential applications in flexible electronic devices such as biosensors, 6 OLED displays, 7 electrochromic windows, 8 and photovoltaics, 9 electrically conducting polymers have recently become the objects of intensive research. Nonetheless, their high contact resistance, difficulties with organic/inorganic patterning, poor adhesion, and several other major and minor issues are still yet to be addressed prior to their fruitful and advantageous use.…”