Substrate temperature dependent performance of near infrared photoresponsive organic field effect transistors based on lead phthalocyanine

• The proportion of triclinic phase in PbPc films increases with rising Tsub.
• The film grains get larger with rising Tsub.
• The increasing proportion of triclinic phase causes a stronger NIR absorption.
• The enlarged film grains give a higher carrier mobility for Tsub ≤ 140 °C.
• An optimal device performance is provided at Tsub = 140 °C.

In order to study the dependence of device performance on substrate temperature (Tsub), lead phthalocyanine (PbPc) photoresponsive organic field-effect transistors were fabricated at different substrate temperatures and characterized. We observed as Tsub rises, the photoresponsivity (R) and the maximum photo/dark current ratio (Pmax) of the devices first increase and then decrease, and an optimal device performance is provided at Tsub = 140 °C, at which the R and Pmax of the device reach maximum simultaneously. This is mainly a result of competition between the enhanced NIR absorption originating from the increasing proportion of triclinic phase in PbPc films with rising Tsub and the decreased carrier mobility at higher substrate temperatures, as evidenced by optical absorption spectrum, X-ray diffraction and atomic force microscopy investigations.

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