Organic Thin-Film Red-Light Photodiodes with Tunable Spectral Response Via Selective Exciton Activation

Red and near-infrared light detection is vital for numerous applications, including full-color imaging, optical communication, and machine vision. However, this development is hindered by a limited choice of small band gap and narrow-bandwidth materials. Here, we report a device principle with a simple organic planar heterojunction architecture that enables a selective activation of excitons for tuning the photoresponse spectra to fabricate thin-film, filterless, red-light organic photodiodes. A sequential solution-processed active layer is formed by depositing the top layer of PC₇₁BM onto the predeposited bottom layer of doped P3HT. By adjusting the ratio of PTB7 in P3HT, an improved responsivity and a red-shift of the photoresponse peak from 645 to 745 nm are demonstrated simultaneously. Furthermore, the responsivity of 745 nm is enhanced over 5 times with a narrow full width at half-maximum of ∼50 nm at optimized doping ratio compared to the pristine PTB7 device. As a result, a high specific detectivity in excess of 10¹² Jones and broad linear dynamic range of 103 dB are achieved. This design concept shows the possibility of realizing tunable red-light selectivity even at relatively thin-film thickness, which is intriguing for the implementation of high-resolution image sensors in the near future.