Triumphing over Charge Transfer Limitations of PEDOT Nanofiber Reduction Catalyst by 1,2-Ethanedithiol Doping for Quantum Dot Solar Cells

Charge transfer between a conducting polymer-based counter electrode (CE) and a polysulfide (S 2– /S n 2– ) electrolyte mediator is a key limitation to improvements of solar energy conversion efficiency (ECE) in quantum-dot-sensitized solar cells (QDSCs). In this paper, 1,2-ethanedithiol (EDT) was doped into nanofibrous poly(3,4-ethylenedioxythiophene) (PEDOT NF) to overcome the charge transfer limitation between PEDOT NF and S 2– /S n 2– . EDT not only helps to reduce the aggregation and thus enhance the linearization of the PEDOT chains but also changes the molecular conformation of the PEDOT chains from a benzoid to a quinoid structure. EDT-doped PEDOT NF-based CEs showed almost 3.7 times higher conductivity, better electrocatalytic activity, and improved compatibility with S 2– /S n 2– in an aqueous electrolyte. As a result, the charge transfer resistance between the polymer-based CE and the S 2– /S n 2– electrolyte was significantly reduced, resulting in over 3% ECE in QDSCs, more than double that of a bare PEDOT NF-based CE.