Organic photodetectors have garnered significant attention due to their broader wavelength of detection, light weight, flexibility, and ease of device processing. In this work, two transistor-type organic photodetectors were developed using pentacene as the active medium. Two dielectric layers, namely hexamethyldisilazane (HMDS) and polymethyl methacrylate (PMMA), at two different substrate temperatures of 25 and 35 °C, were utilized to evaluate the role of the passivation layer and temperature on the growth morphology of pentacene thin film and their photodetection performance. The photo-detecting characteristics including charge carrier mobility, photoresponsivity, photosensitivity, photodetectivity, threshold voltage, Ion − Ioff ratio, and external quantum efficiency, were analyzed for a broadband UV visible spectrum. At higher substrate temperatures, the HMDS-based photodetectors have shown superior performance, achieving maximum mobility and external quantum efficiency values of ~ 6 cm2 V‒1 s‒1 and 13%, respectively, in the UV-A and violet-blue regions of the visible spectrum. Comparatively, reduced performance was observed in PMMA-based devices, which exhibited values of ~ 4 cm2 V‒1 s‒1 and 7%, respectively, at higher substrate temperatures. Under ambient condition, device exhibited Ion − Ioff ratio of 103, photoresponsivity of ~ 2–3 AW‒1, and photodetectivity of order of 108 Jones at 35 °C of substrate temperature. When the drain-source current is in the order of milliampere, the obtained gate current is in the range of nanoampere which is negligible. This demonstrates the effectiveness of both the HMDS and PMMA layers in preventing the leakage current and contribution to the drain-source current, with their lower thickness. The stability tests conducted under ambient conditions revealed that pentacene with HMDS dielectric layer demonstrated better device performance, while with PMMA dielectric layer exhibited superior stability at elevated temperature. The results indicate that by properly engineering the phototransistor with high dielectric and growth morphology, the photodetection characteristics can be tuned and improved. The achieved performances of pentacene thin film devices at higher substrate temperature is comparable and even better in comparison with the reported performances of similar devices.

Influence of substrate temperature and polymer dielectric on broadband photodetection characteristics of pentacene-based phototransistors

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发表日期：

2025年3月13日

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Sreegowri Vishnu Bhat,
Periyasamy Angamuthu Praveen,
Vigneshwaran Selvanathan,
Thangavel Kanagasekaran

摘要

Organic photodetectors have garnered significant attention due to their broader wavelength of detection, light weight, flexibility, and ease of device processing. In this work, two transistor-type organic photodetectors were developed using pentacene as the active medium. Two dielectric layers, namely hexamethyldisilazane (HMDS) and polymethyl methacrylate (PMMA), at two different substrate temperatures of 25 and 35 °C, were utilized to evaluate the role of the passivation layer and temperature on the growth morphology of pentacene thin film and their photodetection performance. The photo-detecting characteristics including charge carrier mobility, photoresponsivity, photosensitivity, photodetectivity, threshold voltage, I_on − I_off ratio, and external quantum efficiency, were analyzed for a broadband UV visible spectrum. At higher substrate temperatures, the HMDS-based photodetectors have shown superior performance, achieving maximum mobility and external quantum efficiency values of ~ 6 cm² V^‒1 s^‒1 and 13%, respectively, in the UV-A and violet-blue regions of the visible spectrum. Comparatively, reduced performance was observed in PMMA-based devices, which exhibited values of ~ 4 cm² V^‒1 s^‒1 and 7%, respectively, at higher substrate temperatures. Under ambient condition, device exhibited I_on − I_off ratio of 10³, photoresponsivity of ~ 2–3 AW^‒1, and photodetectivity of order of 10⁸ Jones at 35 °C of substrate temperature. When the drain-source current is in the order of milliampere, the obtained gate current is in the range of nanoampere which is negligible. This demonstrates the effectiveness of both the HMDS and PMMA layers in preventing the leakage current and contribution to the drain-source current, with their lower thickness. The stability tests conducted under ambient conditions revealed that pentacene with HMDS dielectric layer demonstrated better device performance, while with PMMA dielectric layer exhibited superior stability at elevated temperature. The results indicate that by properly engineering the phototransistor with high dielectric and growth morphology, the photodetection characteristics can be tuned and improved. The achieved performances of pentacene thin film devices at higher substrate temperature is comparable and even better in comparison with the reported performances of similar devices.