Strategic Insights into Semiconducting Polymer Thermoelectrics by Leveraging Molecular Structures and Chemical Doping

Abstract

Thermoelectric (TE) materials can realize the direct transformation between heat and electricity, thereby facilitating the recycling of waste heat. Semiconducting π-conjugated polymers (π-CPs) have been largely explored as organic TE materials thanks to the facile molecular tunability of their electronic properties, their room-temperature solution-processability, their intrinsic low thermal conductivity, and their outstanding mechanical flexibility. In this Focus Review, we describe two key strategieschemical doping and structural tailoringin polymeric TEs for strengthening TE power factors of π-CPs. First, the doping mechanisms are unraveled by a sequential process of charge transfer and free carrier release, followed by the introduction of various doping methods for enhancing the chemical doping. Second, the design principles for polymeric structures including the π-backbone and side-chain engineering are presented. Third, supplementary strategies such as polymer chain alignment and construction of polymer blends are identified. Finally, the existing prime obstacles to future development are discussed and an outlook on feasible solutions to resolving them is provided.

Minimized Energy Loss at the Buried Interface of p‐i‐n Perovskite Solar Cells via Accelerating Charge Transfer and Forming p–n Homojunction

“…When the doping process is over, the F6TCNNQ dopants accept electrons and become F6TCNNQ •− anions while holes left in the polymer film. Commonly, the p-type doping process is occurred spontaneously when the dopant's lowest unoccupied molecular orbital is lower than the HOMO of the hosts (PTAA: 5.13 eV, Poly-TPD: 5.32 eV), [18,20] as shown in Figure 1c. The doping process can be divided into two consecutive procedures including charge transfer and release of free carrier.…”

“…[ 22 ] However, the doping level is limited in a sequential doping system because the dopants are difficult to enter the crystalline domains of polymers. [ 18 ] In this case, the new strategy called anion‐exchange is proposed by Yamashita and co‐workers, which can effectively enhance the doping level of poly(2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene) films. [ 23 ] In the p‐i‐n PVSCs, efficient strategies are needed to be explored to enhance the electrical properties of HTLs, which is of vital importance for enhancing charge transfer efficiency and reducing E loss at the HTL/perovskite buried interface.…”

“…Molecular doping strategies including mixed doping and sequential doping are effective ways to improve the carrier mobility and density of semiconducting polymers. [18,19] For mixed molecular doping strategy, the amount of dopant should be precisely controlled, otherwise excessive dopant will degrade the quality and electronic properties of the polymer film, thus limiting its application. [20,21] Differently, the sequential doping can avoid the presence of excessive dopants and preserve the morphology of polymer films by immersing the as-prepared polymer films into the dopant solutions or vapor-depositing the dopants on their surfaces.…”

Optimizing the doping efficiency and thermoelectric properties of isoindigo-based conjugated polymers using side chain engineering

“…Therefore, considerable research efforts have been devoted to investigating the thermoelectric properties of these polymers, with the goal of improving their performance and developing new applications. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] Inherently conjugated polymers exhibit relatively low s, and chemical doping, which occurs alongside the charge transfer between the host polymer and dopant molecules, is indispensable for increasing the carrier concentration in doped polymer films. The dopants (usually FeCl 3 [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] and 7,7,8,8-tetracyanoquinodimethane (TCNQ) [42][43][44][45][46][47][48][49][50][51][52][53][54] derivative...…”

“…Therefore, considerable research efforts have been devoted to investigating the thermoelectric properties of these polymers, with the goal of improving their performance and developing new applications. 8–25…”