Flexible Si/PEDOT:PSS heterojunction photodetectors with excellent interface contact quality for NIR detection

Flexible Si/PEDOT:PSS heterojunction photodetectors have gained widespread attention due to their excellent performance and low preparation cost, however, the presence of defects on the Si surface that generate surface states and the poor hydrophilicity of PEDOT:PSS that leads to poor contact between Si and PEDOT:PSS have been limiting the performance of the devices; In this study, an inverted pyramidal structure Si substrate with the smaller specific surface area was selected and the Si to PEDOT:PSS interface quality was improved by doping the PEDOT:PSS solution with the fluorosurfactant FC4430 and vinyltrimethoxysilane (VTMO). It was found that the doping of fluorosurfactant FC4430 could reduce the contact angle of PEDOT:PSS solution on IP substrate from 104.5° to 23°, which greatly enhanced the hydrophilicity of PEDOT:PSS without affecting the electrical properties of the films. The doping of VTMO forms Si-O-Si bonds at the Si/PEDOT:PSS interface, which passivates the defects on the silicon surface and at the same time forms a cross-linking network to improve the adhesion of the PEDOT:PSS, which enables the device to exhibit an extremely low dark current of 4.08 × 10−8 mA. Meanwhile, the prepared flexible Si/PEDOT:PSS photodetector exhibits excellent performance, with a responsivity of 8.74 mA/W, a detectivity of 1.21 × 1012 Jones, and a response speed of 120/480 μs under 0 V bias voltage and laser irradiation at a wavelength of 980 nm. Finally, the bending stability of the device was evaluated and the device performance remained above 95 % of the initial value after 50 bending cycles.