We herein report an investigation of ultralarge graphene oxide (UL-GO) sheet/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin composite layers fabricated by spin coating on an indium–tin-oxide (ITO) anode as hole transport layer (HTL) in polymer light-emitting diodes (PLEDs), as well as polymer solar cells (PSCs). Monolayer UL-GOs were first synthesized based on a novel solution-phase method involving pre-exfoliation of graphite flakes which were then mixed into the PEDOT:PSS solution in various specific amounts. The PEDOT:PSS composite film mixed with 0.04 wt% UL-GO by weight exhibits a conductivity of 749.4 S cm⁻¹ and a transmittance of 88.6% at 550 nm. The PEDOT:PSS/GO HTL shows enhanced charge carrier transport because of improved conductivity by the weakening of the coulombic attraction between PEDOT and PSS by the functional groups on GO nanosheets, and the formation of an extended conductive network. Moreover, it can effectively block electrons and reduce resistance in the HTL, leading to better injection and transport of holes and lower turn-on voltage and resulting in a higher overall efficiency in PLEDs. Similarly, it remarkably increases the short circuit current (J_sc), and PSC efficiency because of a remarkable reduction of exciton quenching that results in higher charge extraction in PSCs. The optimized PLEDs and PSCs with a PEDOT:PSS/GO composite HTL layer show a maximum luminosity of 725.6 cd m⁻² (at 10.6 V) for PLEDs, as well as a power conversion efficiency of 3.388% for PSCs, which were improved by ∼11% and 12%, respectively, compared to reference PLEDs and PSCs with a PEDOT:PSS layer.