Sensitive Self-Driven Single-Component Organic Photodetector Based on Vapor-Deposited Small Molecules

Typically, organic solar cells (OSCs) and photodetectors (OPDs) comprise an electron donating and accepting material to facilitate efficient charge carrier generation. This approach has proven successful in achieving high-performance devices but has several drawbacks for upscaling and stability. This study presents a fully vacuum-deposited single-component OPD, employing the neat oligothiophene derivative DCV2-5T in the photoactive layer. Free charge carriers are generated with an internal quantum efficiency of 20 % at zero bias. By optimizing the device structure, a very low dark current of 3.4 · 10^-11 A cm^-2 at -0.1 V is achieved, comparable to the dark current of state-of-the-art bulk heterojunction OPDs. This optimization results in specific detectivities of 1· 10¹³ Jones (based on noise measurements), accompanied by a fast photoresponse (f_-3dB = 200 kHz) and a broad linear dynamic range (> 150 dB). Ultrafast transient absorption spectroscopy unveils that charge carriers are already formed at very short time scales (< 1 ps). The surprisingly efficient bulk charge generation mechanism is attributed to a strong electronic coupling of the molecular exciton and charge transfer states. This work demonstrates the very high performance of single-component OPDs and proves that this novel device design is a successful strategy for highly efficient, morphological stable and easily manufacturable devices.