Developing an effective strategy to suppress dark current for high-performance planar photodetectors

Abstract

The performance of organic photodetectors (OPDs) has been dramatically improved due to the use of bulk heterojunction (BHJ) active layers. However, blending a donor and acceptor in the BHJ film still results in a large extent of bimolecular recombination and increased energetic disorder. This leads to an increase in dark current density (J_d) and a decrease in responsivity (R), which constrains the progress of OPDs towards higher specific detectivity (D*). Herein, in line with the widely-used blend casting (BC) method for BHJ layers, sequential deposition (SD) can also enable similar or even better morphology and device performance for OPDs. Here, we fabricated OPDs with polymer donor PM6 and non-fullerene acceptor BO-4Cl in different structures to investigate the impact of device engineering on molecular stacking and charge recombination. The SD ortho-structured OPD achieved a low J_d of 8.60 × 10⁻⁹ A cm⁻² and D* of 8.76 × 10¹² Jones under −0.1 V bias. More interestingly, by introducing P(VDF-TrFE) as an intrinsic layer to regulate the built-in electric field of the devices, the SD OPDs achieved much lower J_d (1.40 × 10⁻⁹ A cm⁻²) and higher D* (2.26 × 10¹³ Jones) under the same conditions. Our results suggest that the device by the SD method can efficiently suppress the bimolecular recombination and improve crystallization, providing an alternative pathway for developing solution-processed high-performance OPDs.