Effect of hygroscopicity of the hole transport layer on the stability of organic solar cells

Organic solar cells (OSCs) are in high demand due to the need to power micro-powered and wireless indoor electronic devices. However, OSCs have significant disadvantages, such as poor environmental stability, lower efficiency, and low photo stability. Consequently, they have not been commercialized. OSCs are highly dependent on the hole transport layer (HTL). Acidity, hygroscopicity, environmental stability, and the hole transport ability of the HTLs are strongly correlated with the overall performance of OSCs. Many studies have examined how acidity and hole transport capability of HTL affect OSC performance, but hygroscopicity has never been studied. Therefore, in this study, we examined the effect of HTL hygroscopicity on the stability of OSC. Two different materials with the same acidity level—polystyrene sulfonate (PSS)-doped polyaniline (PANI) and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)—were used as an HTL of poly (3-hexylthiophene): [6, 6]-indene-C60 bisadduct active material-based OSC. Thermogravimetric analysis confirmed that PANI:PSS was less hygroscopic than the PEDOT:PSS. Furthermore, the stability study of the OSCs revealed that PANI:PSS based OSC had a longer stability than PEDOT:PSS based OSC.