An External Quantum Efficiency Model of Organic Phototransistors Excluding Photocurrent Amplification Effect

Organic phototransistors (OPTs) are expected to be excellent photodetectors. Currently, the commonly used external quantum efficiency (EQE) of OPTs is equal to the ratio of the number of the photogenerated electrons or holes contributing to photocurrent to that of incident photons. The EQE values calculated by this way are often larger than 100%, which cannot reflect the real photoelectric conversion (PEC) capability of OPTs. The reason for this is that both PEC and non‐PEC current components exist in the photocurrent of OPTs, and the PEC photocurrent component is amplified by the non‐PEC one (that is, a photocurrent amplification (PA) effect). Herein, a basic model for OPTs’ EQE* that excludes the PA effect is proposed based on the PEC process of OPTs. With it, the EQE* models for both single active layer and planar heterojunction OPTs are established, and the EQE* values of them are estimated. The photocurrent of organic phototransistors (OPTs) often consists of non‐photoelectric conversion current (Iph_injection) and photoelectric conversion current (Iph_carrier), and Iph_carrier is amplified significantly by Iph_injection, hence leading to its external quantum efficiency (EQE) to be far larger than 100%. Therefore, it is essential to explore the EQE that only depends on Iph_carrier but not Iph_injection.