Molecular manipulation of PEDOT:PSS for efficient hole transport by incorporation of N-doped carbon quantum dots

Solution-processed poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films have great potential for organic optoelectronic applications due to their high throughput, low cost, and mechanical flexibility. However, the strong acidity and insulating nature of PSS causes a crucial deterioration of device performance. Here, we present an efficient route for addressing the limitations of PSS by molecular manipulation via incorporation of nitrogen-doped carbon quantum dots (N-CQDs) into PEDOT:PSS. The incorporation of N-CQDs significantly reduces resistance, increases work function, modifies the surface energy and smooths the surface morphology of PEDOT:PSS. In our density functional theory (DFT) calculations, inclusion of N-CQDs weakens the electrostatic interaction between PEDOT and PSS, resulting in molecular manipulation of PEDOT:PSS. Compared to conventionally oxidized CQDs (O-CQDs), N-CQDs have better effects in PEDOT:PSS matrices, including 7C-7C stacking with PEDOT and hydrophilic interaction with PSS, which can effectively induce molecular reorientation. The enhancement of charge extraction and charge injection performance of N-CQD-incorporated PEDOT:PSS are demonstrated via organic optoelectronic devices including organic photovoltaics and organic light-emitting diode with significant improvements in power conversion efficiency and quantum efficiency, respectively. Molecular manipulation via the incorporation of N-CQDs holds promise for the development of highly efficient PEDOT:PSS hole-transporting layers in various optoelectronic devices.