Isolated Fe Sites Mediated Construction of WO ₃ Homojunctions for Superior Electronic Sensors

Homojunctions, constructed by different crystal structures or phases of the same material, are widely used in electronic and energy devices. However, the straightforward construction of semiconductor homojunctions by solution methods has been challenging. Herein, as a proof-of-concept, we report an isolated Fe-atom induced growth of hexagonal WO₃ on monoclinic WO₃ by a facile solution process. This approach allows for easy modulation of the ratio of monoclinic to hexagonal phases simply by adjusting the Fe concentration, thereby tuning not only the surface reaction properties but also the electronic conductivity of the materials. As a result, an optimized hexagonal/monoclinic WO₃ homojunction with 0.25 at. % Fe delivers significantly improved response (to 10 ppm of NO₂) by a factor of 65, as well as excellent selectivity, repeatability, and a ppb-level detection of NO₂. This work provides an efficient strategy for designing semiconductor homojunctions and sheds light on the structure-property relationship of homojunctions.