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

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-ethylenedioxythiophene) (PEDOT), varying in molecular weight (Mw) 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 a higher Mw and DL demonstrates 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, work function). On the other hand, the low-quality PEDOT promotes 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, the OSC fabricated with 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 PEDOT in the attainment of highly stable OSCs, but also constitutes a valuable contribution to the existing scientific literature.