Photocrosslinkable bromine-functionalized poly(3-hexylthiophene) (P3HT-Br) copolymers designed for application in solution-processed organic photovoltaics are prepared by copolymerization of 2-bromo-3-(6-bromohexyl) thiophene and 2-bromo-3-hexylthiophene. The monomer ratio is carefully controlled to achieve a UV photocrosslinkable layer while retaining the π–π stacking feature of the conjugated polymers. The new materials are used as electron donors in both bulk heterojunction (BHJ) and bilayer type photovoltaic devices. Unlike devices prepared from either P3HT:PCBM blend or P3HT-Br:PCBM blend without UV treatment, photocrosslinked P3HT-Br:PCBM devices are stable even when annealed for two days at the elevated temperature of 150 °C as the nanophase separated morphology of the bulk heterojunction is stabilized as confirmed by optical microscopy and grazing incidence wide angle X-ray scattering (GIWAXS). When applied to solution-processed bilayer devices, the photocrosslinkable materials show high power conversion efficiencies (∼2%) and excellent thermal stability (3 days at 150 °C). Such performance, one of the highest obtained for a bilayer device fabricated by solution processing, is achieved as crosslinking does not disturb the π–π stacking of the polymer as confirmed by GIWAXS measurements. These novel photocrosslinkable materials provide ready access to efficient bilayer devices thus enabling the fundamental study of photophysical characteristics, charge generation, and transport across a well-defined interface.

http://absimage.aps.org/image/MAR09/MWS_MAR09-2008-000095.pdf

Photo-crosslinkable Polythiophenes for Efficient Thermally Stable Organic Photovoltaics

A series of polymer photodetectors with device configuration of ITO/PEDOT:PSS/P3HT:PC61BM/C60/Al were prepared by using P3HT as the donor material and PC61BM as the acceptor material. By regulating the content of 1,8-diiodooctane (DIO) (V/V: 1%, 3%, 5%) as a processing additive, the morphology of the active layer can be greatly improved. With C60 as the hole blocking layer, the dark current density of the device can be reduced by about an order of magnitude. When employing 3% DIO (V/V) in the active layer processing, the photodetetcors present the best performance, and the detectivity of the device is 1.52×1012 Jones at 540 nm under a bias of −0.1 V. Moreover, it also has a wider linear dynamic range of 60 dB as well as faster response speed (τr/τf=0.53/0.71 µs) than those of devices with other content of DIO additives.

Effect of 1,8-Diiodooctane Content on the Performance of P3HT:PC61BM Bulk Heterojunction Photodetectors

In recent years, nanoparticulate materials have aroused interest in the field of organic electronics due to their high versatility which increases the efficiency of devices. In this work, four different stable conformations based on the organic semiconductors P3HT and PC71BM were synthesized using the nanoprecipitation method, including blend and core-shell nanoparticles. All nanoparticles were obtained free of surfactants and in aqueous suspensions following the line of ecologically correct routes. The structural and optoelectronic properties of the nanoparticles were investigated by dynamic light scattering (DLS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV-visible absorption spectroscopy and UV-visible photoluminescence (PL). Even in aqueous media, the blend and core-shell nanoparticles exhibited a greater light absorption capacity, and these conformations proved to be effective in the process of dissociation of excitons that occurs at the P3HT donor/PC71BM acceptor interface. With all these characteristics and allied to the fact that the nanoparticles are surfactant-free aqueous suspensions, this work paves the way for the use of these colloids as a photoactive layer of organic photovoltaic devices that interface with biological systems.

/pdf/synthesis-of-organic-semiconductor-nanoparticles-with-3tmwceiz.pdf

Synthesis of Organic Semiconductor Nanoparticles with Different Conformations Using the Nanoprecipitation Method

Different quantum dot (QD)-based supramolecules subsuming crab-shape poly(3-hexylthiophene) (P3HT) short chain/graphene quantum dot (GQD) and half crab-shape P3HT short chain/carbon quantum dot (CQD), patterned P3HT/GQD and P3HT/CQD long chain, fibrillar P3HT/GQD, and fibrillar P3HT/CQD nanostructures were fabricated to stabilize P3HT:[6,6]-phenyl C71 butyric acid methyl ester (PC71BM) solar cells during air aging. The P3HT crystals were composed of face-on ((100) and (002) prisms) and edge-on ((020) and (002) growth planes) oriented chains with distinct qualities of crystallinity. Within 1.5 months of aging in 36% humidity at 34°C, P3HT:PC71BM photovoltaics and some of their modified states were no longer applicable and went down to 0% efficacy. Only the photoactive layers modified by the fibrillar P3HT/CQD (1.74% and 790 Ω cm2), crab-shape P3HT/GQD (0.45% and 896 Ω cm2), patterned P3HT/GQD (0.29% and 918 Ω cm2) and fibrillar P3HT/GQD (3.39% and 670 Ω cm2) supramolecules reflected non-zero performances. The decreasing slopes of photovoltaic characteristics versus the aging time were the slowest for the fibrillar P3HT/GQD-based solar cells, and performances of 6.50% (14.05 mA cm−2, 66.11%, and 0.70 V), 5.70% (13.34 mA cm−2, 62.79%, and 0.68 V), 4.53% (12.51 mA cm−2, 56.60%, and 0.64 V) and 3.39% (11.67 mA cm−2, 51.83%, and 0.56 V) were recorded during 0, 30, 60 and 90 days of air aging, respectively. Single crystallinity of P3HT fibrils, on one hand, and flat structure of GQDs, on the other hand, were the origins of this phenomenon. More stabilized photovoltaics depicted longer half-life with respect to less stabilized ones, e.g., 93 versus 19 days for P3HT:PC71BM:fibrillar P3HT/GQD and P3HT:PC71BM systems, respectively.

https://link.springer.com/content/pdf/10.1007/s11664-021-09182-2.pdf

Zunju Zhang

Papers

Improved stability in P3HT:PCBM photovoltaics by incorporation of well-designed polythiophene/graphene compositions