Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) serves as one of the most common choice for the hole transport layer (HTL) in organic solar cells (OSCs), offering distinct advantages including water processability, optical transparency, and easy commercial availability. However, the hygroscopic nature of the PSS component in PEDOT:PSS can lead to moisture absorption, resulting in the formation of pinholes and charge recombination sites at the interface, which significantly deteriorate device performance and stability. OSC devices with the modified HTL by simple thermal crosslinking method maintained comparable photovoltaic performance to conventional PEDOT:PSS-based ones, while exhibiting significantly enhanced water resistance, operational stability, and mechanical robustness. This approach offers a simple and effective way toward high-efficiency, long-lifetime OSCs.