PEDOT quality: another key factor determining the thermal stability of organic solar cells

Abstract

Understanding the key factors influencing the stability of organic solar cells (OSCs) is imperative for the advancement of organic electronics. Herein, a range of poly(3,4-ethylenedioxythiophenes) (PEDOTs), varying in the molecular weight (M_w) and doping level (DL), were synthesized to unveil the impact of the quality of PEDOT hole transporting materials (HTMs) on the thermal stability of OSCs for the first time. It is shown that higher M_w and DL values demonstrate enhanced efficacy in preserving the p-doping characteristics of PEDOTs during thermal aging, thereby enabling the HTM to manifest more stable electrical properties (i.e. conductivity and work function). On the other hand, low-quality PEDOTs promote the formation of larger crystalline structures in the active layer, which are more susceptible to decomposition during thermal aging. Both effects contribute to the achievement of exceptional device stability, as demonstrated by a low efficiency decay rate of approximately 28%. However, an OSC fabricated with a moderate-quality PEDOT exhibits a high decay rate of 38% due to the trade-off between these two effects. This study not only showcases a promising future for precise quality control of PEDOTs in the attainment of highly stable OSCs, but also constitutes a valuable contribution to the existing scientific literature.