Highly Passivated n‐Type Colloidal Quantum Dots for Solution‐Processed Thermoelectric Generators with Large Output Voltage

• Published in: Advanced energy materials Vol. 9; no. 28
• Main Authors: Nugraha, Mohamad I., Kim, Hyunho, Sun, Bin, Desai, Saheena, de Arquer, F. Pelayo Garcia, Sargent, Edward H., Alshareef, Husam N., Baran, Derya
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.07.2019
• Subjects: colloidal quantum dots; Colloiding; Electric potential; ligands; n‐type thermoelectrics; Power factor; Quantum dots; Seebeck effect; solution‐processed semiconductors; Thermal conductivity; Thermoelectric generators; Thermoelectric materials; Voltage
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.201901244

Colloidal quantum dots (CQDs) are attractive materials for thermoelectric applications due to their simple and low‐cost processing; advantageously, they also offer low thermal conductivity and high Seebeck coefficient. To date, the majority of CQD thermoelectric films reported upon have been p‐type, while only a few reports are available on n‐type films. High‐performing n‐ and p‐type films are essential for thermoelectric generators (TEGs) with large output voltage and power. Here, high‐thermoelectric‐performance n‐type CQD films are reported and showcased in high‐performance all‐CQD TEGs. By engineering the electronic coupling in the films, a thorough removal of insulating ligands is achieved and this is combined with excellent surface trap passivation. This enables a high thermoelectric power factor of 24 µW m−1 K−2, superior to previously reported n‐type lead chalcogenide CQD films operating near room temperature (<1 µW m−1 K−2). As a result, an all‐CQD film TEG with a large output voltage of 0.25 V and a power density of 0.63 W m−2 at ∆T = 50 K is demonstrated, which represents an over fourfold enhancement to previously reported p‐type only CQD TEGs. Efficient n‐type colloidal quantum dot (CQD) thermoelectric films are realized by engineering the interdot electronic coupling using halide salts that allow a thorough removal of insulating ligands. In combination with excellent surface trap passivation, this strategy leads to a high electrical conductivity of 12 S cm−1 and enables the fabrication of all‐CQD p–n thermoelectric generator with large output voltage.