Gold nanoparticles (Au NPs) at larger sizes (e.g. >5 nm) are extensively utilised across various fields, including biology, medicine, optoelectronics, and Raman signal enhancement. This study demonstrates that incorporating colloidal Au NPs within methylammonium lead iodide (MAPI) perovskite and amorphous selenium (a-Se) devices enhances their optical response and direct X-ray detection. Direct detection X-ray systems convert X-ray photons into electrical signals without an intermediate step, offering superior image quality with high resolution and detail. These systems exhibit increased sensitivity and efficiency over indirect detection methods, helping to minimise radiation exposure to patients. It also enables rapid image acquisition and reduced noise, making them essential within dynamic imaging scenarios. 

The primary materials researched for creating these direct detection devices include a-Se, silicon and, recently, perovskites. Au NPs have gained prominence in optical detection and power conversion, notably improving power conversion efficiency in perovskite solar cells and enhancing detector properties under optical illumination. The main explanation for this enhancement is the plasmon field effect, which aligns well for optical use cases, but in the realm of X-rays, the Auger effect also becomes a subject of interest. 

Our approach used a MAPI solar cell device as a template (ITO/SnO₂/MAPI/Spiro-Li/Au). We introduced colloidal Au NPs into the perovskite precursor solution. For Solar Cell performance, our reference device obtained a champion PCE of 15.8%, and the champion device with Au NP reached 16.8%. Under X-rays generated by a Cu source, an 80% increase in X-ray sensitivity was achieved by adding the AU NPs. For a-Se devices, the NPs were applied via drop-casting between layers of thermally vapour-deposited a-Se. The peak optical response of the a-Se devices had a maximum increase of 2.5 times, with a strong Au NP size dependence. For the X-ray response of the a-Se devices, while Au NPs alone did not enhance X-ray response, adding a scintillator on the device surface led to a more than 50% increase in X-ray signal.