N-type organic thermoelectrics: demonstration of ZT > 0.3

Abstract

The ‘phonon-glass electron-crystal’ concept has triggered most of the progress that has been achieved in inorganic thermoelectrics in the past two decades. Organic thermoelectric materials, unlike their inorganic counterparts, exhibit molecular diversity, flexible mechanical properties and easy fabrication, and are mostly ‘phonon glasses’. However, the thermoelectric performances of these organic materials are largely limited by low molecular order and they are therefore far from being ‘electron crystals’. Here, we report a molecularly n-doped fullerene derivative with meticulous design of the side chain that approaches an organic ‘PGEC’ thermoelectric material. This thermoelectric material exhibits an excellent electrical conductivity of >10 S cm−1 and an ultralow thermal conductivity of <0.1 Wm−1K−1, leading to the best figure of merit ZT = 0.34 (at 120 °C) among all reported single-host n-type organic thermoelectric materials. The key factor to achieving the record performance is to use ‘arm-shaped’ double-triethylene-glycol-type side chains, which not only offer excellent doping efficiency (~60%) but also induce a disorder-to-order transition upon thermal annealing. This study illustrates the vast potential of organic semiconductors as thermoelectric materials.

Revisiting doping mechanisms of n-type organic materials with N-DMBI for thermoelectric applications: Photo-activation, thermal activation, and air stability

“…In another article, a slight gain of mass above 90°C was evidenced and assigned to oxidation. 18 To shed light on the behaviour of N-DMBI upon thermal annealing, we heated up N-DMBI-H powder at 120°C for 2 hours in ambient conditions and analysed the residue without purification. The UV-Vis absorbance and NMR spectra of the residue are compared to the signatures of the neat N-DMBI-H, the N-DMBI + cation and the crystal 3 mainly composed of the amide derivative (Figure 4).…”

“…15 It was associated with various hosts such as carbon nanotubes 16 , conductive polymers 17 , and fullerene derivatives which led to the highest figure of merit ever reported for single-host organic thermoelectrics (ZT = 0.34 at 120°C). 18 We summarized some recent uses of N-DMBI-H in the organic thermoelectric field in Table S1.…”

Amphipathic Side Chain of a Conjugated Polymer Optimizes Dopant Location toward Efficient N‐Type Organic Thermoelectrics

“…The carrier density is modulated by molecular doping, which often involves a redox reaction with a strong reducing agent (n-type dopant). [13][14][15][16][17] As such, the quest for n-type conjugated polymers with high electron mobility and large electron affinity has become an obvious way to advance n-type polymeric thermoelectrics. Fortunately, molecular strategies for tuning transport properties and energetics have been extensively investigated in other research fields such as organic field-effect transistors and organic photovoltaics, [18,19] and abundant experience has been accumulated.…”

Thermoelectric Materials: Current Status and Future Challenges

“…(Lu et al, 2021) Interestingly, the vinyl derivative of the same polymer (TBDPPV) exhibited a higher maximum electrical conductivity of 90 S cm -1 compared to TBDOPV-T, however the optimal recorded PF is slightly lower with a value of 76 μW m -1 K -2 , but is still among the highest performing n-type organic polymers to date. In terms of zT which is less frequently reported for organic materials than the power factor, due to the challenges associated with accurately measuring the thermal conductivity, the current best performing organic thermoelectric materials have zT-values of 0.42 (ptype) (Kim et al, 2013) and 0.34 (n-type) (Liu et al, 2020a) at room temperature and 120 C, respectively.…”