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, machine vision, etc. However, this development is hindered by a limited choice of small bandgap and narrow bandwidth materials. Here, we report a device principle with a simple organic planar heterojunction architecture which enables a selective activation of excitons for tuning the photoresponse spectra to fabricate thin-film, filter-less, red-light organic photodiodes. A sequential solution-processed active layer is formed by depositing the top layer of PC71BM onto the pre-deposited bottom layer of doped P3HT. By adjusting the ratio of PTB7 in P3HT, an improved responsivity and a red-shift of photoresponse peak from 645 nm to 745 nm are demonstrated simultaneously. Furthermore, the responsivity of 745 nm is enhanced over 5 times with narrow full-width-at-half-maximum of ~50 nm at optimized doping ratio compared to pristine PTB7 device. As a result, a high specific detectivity in excess of 10^12 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.