Post‐Treated Self‐Assembled Monolayer‐Driven Low‐Noise Self‐Powered Organic Photonic Conversion Devices

Combining energy harvesting and photodetection within a single organic device enables self‐powered sensing platforms to be built around integrated photodetector (PD) photovoltaics. The hole transport layer (HTL) of these devices governs the charge extraction dynamics that determine their performance. [2‐(9H‐carbazol‐9‐yl)ethyl]phosphonic acid (2PACz), a widely used self‐assembled monolayer HTL offering a modified work function (WF) and simple solution processing, forms surface aggregates during deposition that degrade the interfacial uniformity and raise the trap density at the hole‐extracting contact. To address this limitation, a posttreatment with 2‐chloronicotinic acid (INA) is applied to the 2PACz interface. INA reduces the surface aggregates and restores the interfacial uniformity while preserving the established ability of 2PACz to modify the WF. A PM6:L8‐BO‐based device using a treated interface delivers power conversion efficiencies of 16.7% under 1‐sun (AM 1.5 G) and 29.8% under 1000 lx illumination (2700 K LED) in the PV mode. In self‐powered PD mode, the treated device exhibits low noise current of 9.19 fA and a directly measured noise equivalent power of 40.4 fW (device area = 0.1 cm 2 , bandwidth = 1 Hz), corresponding to a specific detectivity of 7.81 × 10 12 cm·Hz 1/2 ·W −1 and a linear dynamic range of 147.7 dB.