Achieving high electrical conductivity and thermoelectric power factor simultaneously for n‐type organic thermoelectrics is still challenging. By constructing two new acceptor‐acceptor n‐type conjugated polymers with different backbones and introducing the 3,4,5‐trimethoxyphenyl group to form the new n‐type dopant 1,3‐dimethyl‐2‐(3,4,5‐trimethoxyphenyl)‐2,3‐dihydro‐1H‐benzo[d]imidazole (TP‐DMBI), high electrical conductivity of 11 S cm−1 and power factor of 32 μW m−1 K−2 are achieved. Calculations using Density Functional Theory show that TP‐DMBI presents a higher singly occupied molecular orbital (SOMO) energy level of −1.94 eV than that of the common dopant 4‐(1, 3‐dimethyl‐2, 3‐dihydro‐1H‐benzoimidazol‐2‐yl) phenyl) dimethylamine (N‐DMBI) (−2.36 eV), which can result in a larger offset between the SOMO of dopant and lowest unoccupied molecular orbital (LUMO) of n‐type polymers, though that effect may not be dominant in the present work. The doped polymer films exhibit higher Seebeck coefficient and power factor than films using N‐DMBI at the same doping levels or similar electrical conductivity levels. Moreover, TP‐DMBI doped polymer films offer much higher electron mobility of up to 0.53 cm2 V−1 s−1 than films with N‐DMBI doping, demonstrating the potential of TP‐DMBI, and 3,4,5‐trialkoxy DMBIs more broadly, for high performance n‐type organic thermoelectrics.
A novel n‐type copolymer dopant polystyrene–poly(4‐vinyl‐N‐hexylpyridinium fluoride) (PSpF) with fluoride anions is designed and synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. This is thought to be the first polymeric fluoride dopant. Electrical conductivity of 4.2 S cm–1 and high power factor of 67 µW m–1 K–2 are achieved for PSpF‐doped polymer films, with a corresponding decrease in thermal conductivity as the PSpF concentration is increased, giving the highest ZT of 0.1. An especially high electrical conductivity of 58 S cm–1 at 88 °C and outstanding thermal stability are recorded. Further, organic transistors of PSpF‐doped thin films exhibit high electron mobility and Hall mobility of 0.86 and 1.70 cm2 V–1 s–1, respectively. The results suggest that polystyrene–poly(vinylpyridinium) salt copolymers with fluoride anions are promising for high‐performance n‐type all‐polymer thermoelectrics. This work provides a new way to realize organic thermoelectrics with high conductivity relative to the Seebeck coefficient, high power factor, thermal stability, and broad processing window.
Colloidal
quantum dot (CQD) solar cells have benefited from rapidly
rising single-junction efficiencies in recent years and have shown
promise in multijunction and color-tuned applications. However, within
the context of next-generation solar cells, CQD photovoltaics still
have an efficiency deficit compared to mature technologies. Here,
we use one-dimensional optoelectronic solar cell simulations to show
that much of this efficiency deficit in the highest-performing PbS
CQD solar cells can be attributed to the hole transport layer (HTL).
We find that increasing both the doping density and, counterintuitively,
the electron mobility in this layer should have the largest impact
on performance, attributed to the nontrivial role that the HTL plays
in photon absorption. We use stoichiometry control through sulfur
infusion of the standard CQD HTL materials to improve the carrier
mobilities and doping density. This work resulted in a clear performance
improvement, to 10.4% power conversion efficiency in the best device.
Nominally p-doped conductive polymers that display n-type Seebeck coefficients are intriguing because of the possibly high n-type power factors and the complex p-to-n switching mechanism. This study reports a diketopyrrolopyrrole (DPP strong acceptor)-based polymer with a dichlorinated dithienylethene (ClTVT) weak donor unit sequentially doped with solutions of varied FeCl 3 concentrations as a p-n switchable thermoelectric. Polymer films doped with dilute and moderate FeCl 3 solution concentrations (up to 40 mmol/L) exhibit positive (ca. 100 μV/K) and negative (ca. tens of μ/K) Seebeck coefficients and high electrical conductivities of 80 and 130 S cm −1 , respectively. After rinsing, the conductivity increases to 170 S cm −1 for both p-type and ntype, with Seebeck coefficients slightly more positive/less negative and Seebeck voltage time evolution consistent with their being completely electronic. The power factor of 15 μW/m K 2 was unusually high for a p-to-n inversion material. However, polymer films doped with a high-concentration FeCl 3 solution (50 mmol/L) without rinsing show a high composite Seebeck coefficient of −2400 μV K −1 . We propose that this high Seebeck coefficient arises from a contribution of Cl-ion thermodiffusion in a near-surface layer. Supporting evidence for this is an analogous, even higher negative Seebeck coefficient obtained from the much less conjugated/conductive polymer poly(p-phenylene oxide) (PPO) on which FeCl 3 was applied to form a layer that was removed on rinsing.
N‐Type thermoelectrics typically consist of small molecule dopant+polymer host. Only a few polymer dopant+polymer host systems have been reported, and these have lower thermoelectric parameters. N‐type polymers with high crystallinity and order are generally used for high‐conductivity (
σ
${\sigma }$
) organic conductors. Few n‐type polymers with only short‐range lamellar stacking for high‐conductivity materials have been reported. Here, we describe an n‐type short‐range lamellar‐stacked all‐polymer thermoelectric system with highest
σ
${\sigma }$
of 78 S−1, power factor (PF) of 163 μW m−1 K−2, and maximum Figure of merit (ZT) of 0.53 at room temperature with a dopant/host ratio of 75 wt%. The minor effect of polymer dopant on the molecular arrangement of conjugated polymer PDPIN at high ratios, high doping capability, high Seebeck coefficient (S) absolute values relative to
σ
${\sigma }$
, and atypical decreased thermal conductivity (
κ
${\kappa }$
) with increased doping ratio contribute to the promising performance.
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