Improved performance of lead phthalocyanine phototransistor by template inducing effect based on optimized-thickness copper phthalocyanine layers

Organic phototransistors (OPTs) have captured a growing attention over the years due to their advantages of lightweight, flexibility, low cost and large area fabrication. Especially, how to improve the single-layer device performance is an essential issue. Here, we report that the performance of lead phthalocyanine (PbPc) single-layer near-infrared OPT was improved by inserting different-thickness (1, 2.5, 5 and 8 nm) copper phthalocyanine (CuPc) template inducing layers (TILs). We found that different-thickness CuPc TILs present different continuity and the corresponding PbPc films show different crystallinity, exhibiting different template inducing effects. The maximum mobility, photoresponsivity, specific detectivity and photosensitivity of 8.6 × 10−5 cm2V−1s−1, 2.3 A/W, 4.0 × 1011 Jones and 82.7, respectively, were obtained when the thickness of CuPc TIL is 2.5 nm rather than that of 0, 1, 5 and 8 nm. This may be because the 2.5-nm CuPc TIL that is quasi-continuous and highly ordered approximate-monolayer produces an optimal template inducing effect, and therefore the upper PbPc film holds the highest triclinic crystallinity and content, resulting in the highest carrier mobility and the highest near-infrared light absorption efficiency in the series of OPTs. This work can provide a guideline for improving the performance of single-layer organic photodetectors.