Graphitic Carbon Nitride Nanostructures as Molecular Modifier for PEDOT:PSS Hole Transport Layer in Polymer Solar Cells

In this article, we introduced graphitic carbon nitride (g-C
₃
N
₄
), a two-dimensional graphene-like material, tuning electronic properties of PEDOT:PSS via secondary doping. The incorporation of g-C
₃
N
₄
nanosheets (NS) and quantum dots (QDs) to the aqueous solution of PEDOT:PSS weakens the coulombic interaction between PEDOT and PSS chains, leading to the formation of expanded coil/linear conformational structure. Thereby, increasing the conductivity of doped PEDOT:PSS films by 75% and 30%, respectively, for the optimal doping concentrations of NS and QDs. The polymer solar cell employing these films as hole transport layer (HTL) yielded the power conversion efficiency of 7.65% and 6.44% for NS and QDs, respectively, compared to 5.45% for the reference devices with pristine PEDOT:PSS as HTL. This improvement in photovoltaic performance can be attributed to the increase in short circuit current, carrier mobility, fill factor, and reduced series resistance. The reduced contact barrier, owing to smooth NS and QDs modified HTL, facilitates the charge transport by reducing the overall device resistance by 88% and 30% for NS and QDs, respectively. The modification in the molecular structure of PEDOT:PSS because of the incorporation of NS and QDs resulted in improved device stability retaining almost 40% of the initial PCE even after 200 min of continuous illumination. The results demonstrate a systematic strategy of improving the conductivity and mobility of HTL, resulting in enhanced device performance.