Abstract In this study a high‐performance hybrid X‐ray detector incorporating CdSe nanoplatelets (NPLs) is presented into a PBDB‐T(Poly[[4,8‐bis[5‐(2‐ethylhexyl)‐2‐thienyl]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl]‐2,5‐thiophenediyl[5,7‐bis(2‐ethylhexyl)‐4,8‐dioxo‐4H,8H‐benzo[1,2‐c:4,5‐c′]dithiophene‐1,3‐diyl]]polymer):ITIC (2,2′‐[[6,6,12,12‐Tetrakis(4‐hexylphenyl)‐6,12‐dihydrodithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene‐2,8‐diyl]bis[methylidyne(3‐oxo‐1H‐indene‐2,1(3H)‐diylidene)]]bis[propanedinitrile])organic semiconductor matrix. Organic semiconductors offer advantages such as flexibility and low‐cost fabrication, but their limited X‐ray sensitivity restricts their application in radiation detection. To overcome this, hybrid active layers incorporating inorganic nanomaterials such as CdSe nanoplatelets have emerged as promising candidates for enhancing performance. The 5‐monolayer CdSe NPLs are synthesized with precise thickness control, exhibiting strong absorption and photoluminescence at 556 nm, which effectively matches the emission spectrum of CsI(Tl) scintillators. The hybrid active layer is optimized by investigating various PBDB‐T:ITIC ratios and CdSe NPLs concentrations. The optimal device configuration, achieved with a 1:1 ratio of PBDB‐T:ITIC and 1.5 mg of CdSe NPLs, demonstrates a power conversion efficiency of 7.18% and a photocurrent density of 18.74 mA/cm − 2 . The incorporation of CdSe NPLs enhanced the X‐ray detector's sensitivity by 31.9% compared to the pure organic device, reaching 1.86 mA/Gy cm − 2 . The enhanced performance is attributed to the improved light absorption and charge transport properties of the hybrid active layer, despite a slight increase in surface roughness. This work demonstrates the potential of organic–inorganic hybrid systems for next‐generation X‐ray detection applications.