<p>Solar dryers are challenged to maintain a homogeneous drying air temperature because cloud cover and rapid fluctuations in solar radiation disrupt heat supply, reducing efficiency and process reliability. Integrating phase change materials (PCMs) provides thermal energy storage that reduces these variations and limits temperature drops during low solar radiation periods. In this work, a double pass solar air heater (DPSAH) drying system was developed and tested under real outdoor conditions to achieve more stable and effective drying of agricultural products. An eco-friendly eutectic PCM doped with hexagonal boron nitride (hBN) and graphene (GN) nanoparticles was incorporated into the DPSAH and connected to a drying cabinet to promote uniform drying. Field experiments were performed on Urfa pepper in Şanlıurfa, Türkiye, a hot climate region locally. Experiments were performed at inlet air velocities of 3 m·s⁻¹, 6 m·s⁻¹, and 9 m·s⁻¹ using a two-step charging-discharging process. At each air velocity, four DPSAH dryers were compared against open sun drying. The results showed that GN-doped PCM significantly improved the drying performance. At an inlet air velocity of 6 m·s⁻¹, the PCM-GN integrated DPSAH (DG) configuration delivered the highest performance, achieving a useful heat gain of 462.6 W and an average thermal efficiency of 83.4&#xa0;%. In addition, the lowest moisture and water activity, as well as the best color preservation and highest antioxidant values, were obtained for the DG configuration at an inlet air velocity of 6 m·s⁻¹. Results confirmed that improved heat transfer in nanoparticle-doped PCM directly improved overall system performance significantly.</p>