Efficient transparent organic light-emitting diodes (OLEDs) with improved stability based on conductive, transparent poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) electrodes are reported. Based on optical simulations, the device structures are carefully optimized by tuning the thickness of doped transport layers and electrodes. As a result, the performance of PEDOT:PSS-based OLEDs reaches that of indium tin oxide (ITO)-based reference devices. The efficiency and the long-term stability of PEDOT:PSS-based OLEDs are significantly improved. The structure engineering demonstrated in this study greatly enhances the overall performances of ITO-free transparent OLEDs in terms of efficiency, lifetime, and transmittance. These results indicate that PEDOT:PSS-based OLEDs have a promising future for practical applications in low-cost and flexible device manufacturing.