The question of designing high electron mobility polymers by increasing the planarization using diffusive nonbonding heteroatom interactions in diketopyrrolopyrrole polymers is addressed in this. For this, three different diketopyrrolo[3,4‐c]pyrrole (DPP) derivatives with thienyl‐, 2‐pyridinyl‐, and phenyl‐flanked cores are copolymerized with an electron‐rich thiophene unit as well as an electron‐deficient 3,4‐difluorothiophene unit as comonomer to obtain diverse polymeric DPPs which vary systematically in their structures. The crystallinity differs significantly with clear trends on varying both flanking unit and comonomer. The optical gap and energy levels depend more on the nature of the flanking aryl units rather than on fluorination. Additionally, the charge transport properties are compared using different methods to differentiate between interface or orientation effects and bulk charge carrier transport. In organic field effect transistor devices with very high electron as well as hole mobilities (up to 0.6 cm2 V−1 s−1) are obtained and fluorination leads to a more pronounced n‐type nature in all polymers, resulting in ambipolar behavior in otherwise p‐type materials. In contrast, space‐charge limited current measurements show a strong influence of the flanking units only on electron mobilities. Especially, the elegant synthetic strategy of combining pyridyl flanking units with difluorothiophene as the comonomer culminates in a record bulk electron mobility of 4.3 × 10−3 cm2 V−1 s−1 in polymers.
We report a systematic investigation on the role of excess PbI content in CHNHPbI perovskite film properties, solar cell parameters and device storage stability. We used the CHNHI vapor assisted method for the preparation of PbI-free CHNHPbI films under a N atmosphere. These pristine CHNHPbI films were annealed at 165 °C for different time intervals in a N atmosphere to generate additional PbI in these films. From XRD measurements, the excess of PbI was quantified. Detailed characterization using scanning electron microscopy, X-ray diffraction, UV-Visible and photoluminescence for continuous aging of CHNHPbI films under ambient condition (50% humidity) is carried out for understanding the influence of different PbI contents on degradation of the CHNHPbI films. We find that the rate of degradation of CHNHPbI is accelerated due to the amount of PbI present in the film. A comparison of solar cell parameters of devices prepared using CHNHPbI samples having different PbI contents reveals a strong influence on the current density-voltage hysteresis as well as storage stability. We demonstrate that CHNHPbI devices do not require any residual PbI for a high performance. Moreover, a small amount of excess PbI, which improves the initial performance of the devices slightly, has undesirable effects on the CHNHPbI film stability as well as on device hysteresis and stability.
Doped semiconductor polymers are gaining huge interest as materials in future energy conversion applications such as low-power polymeric thermoelectrics (TEs), because they are light weight, flexible, printable, and suitable for large area applications like wearable technologies. [1-4] The basic challenge in TE, however, lies in efficient doping of the organic semiconductors (OSCs), because OSCs have extremely low intrinsic charge carrier concentrations and hence very low electrical conductivities in the range of 10 −6 to 10 −12 S cm −1. Molecular doping, [5] commonly used to increase the electrical conductivities of OSCs, involves the addition of a redox active organic or inorganic molecule as dopant. These dopants are capable of accepting (for p-type doping) or donating electrons to OSCs (for n-type doping), thereby generating free holes or electrons in OSCs. For p-type doping, acceptor dopants such as I 2 , [6] FeCl 3 , [7] molybdenum tris(1,2-bis(trifluoromethyl) ethane-1,2-dithiolene) (Mo(tfd) 3), [8] tetrafluorotetracyano-quinodimethane (F 4 TCNQ) and
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