Benefiting from the capability to translate ultraviolet optical signals into electrical outputs, ultraviolet photodetectors (UV PDs) have aroused tremendous research concerns and been widely applied in environmental monitoring, military reconnaissance, space exploration and biopharmaceutical detection. Photogenerated carrier non-radiative recombination is one of the most critical challenges restricting the photoelectric conversion efficiency, detection sensitivity and stability of semiconductor PDs. This study investigates the bio-hybrid behavior of pyomelanin secreted with Pseudoalteromonas lipolytica (P. lipolytica) as an electron transport layer (ETL) on SnO2, elucidates the mechanism by which pyomelanin enhances the performance of FTO/ SnO2/pyomelanin/Au PDs, and explores the work function modulation process of pyomelanin as a potential alternative ETL material. Bacterially secreted pyomelanin is isolated and purified, and heterojunctions are constructed with SnO2 thin films via spin-coating, followed by fabrication of vertical-structure PDs. The biohybrid behavior of pyomelanin on the semiconductor is characterized by surface morphology, phase structure, electrical, optical, and band-structure measurements. The photodetection performance is evaluated under different visible wavelengths, light intensities, pyomelanin annealing temperatures, and applied bias voltages.
Results show that the SnO2 thin film on FTO consists of uniform rutile SnO2 nanoparticles in 20-50 nm. The spin-coated pyomelanin layer exhibits good coverage and integrity, forming a Schottky contact with SnO2. With the increase of the annealing temperature, the electrical conductivity of pyomelanin increases while its work function decreases. The photodetection performance is achieved at a pyomelanin annealing temperature of 60 ℃. At a bias of -2 V, the responsivity and specific detectivity reach 54.20 × 103 mA/W and 4.58 × 1015 Jones, respectively. Compared with the device without pyomelanin, the photoresponse is enhanced by a fold of 3.10, and the dark current is reduced by a fold of 9.30. The device demonstrates excellent weak-light detection capability and high durability upon long-term (500 days) exposure to ambient air and exhibits photoresponse in the visible range of 400-600 nm, enabling multi-band detection.
The performance enhancement mechanism is systematically analyzed as follows: Abundant polar groups contained in pyomelanin effectively improve the solution wettability and film-forming quality on the semiconductor surface, which greatly mitigates interfacial defect states originating from the high specific surface area of SnO2 nanoparticles. Combined with its favorable intrinsic electrical conductivity, pyomelanin significantly accelerates the interfacial transmission of photogenerated electrons. Benefiting from the unique reversible redox cycling characteristic of pyomelanin, the pyomelanin layer efficiently promotes internal electron migration and severely suppresses the non-radiative recombination of photogenerated electron-hole pairs, which fundamentally improves the photoelectric conversion efficiency. Moreover, a narrow-bandgap organotin intermediate phase with a band gap (Eg) of lower than 1.88 eV is formed at the pyomelanin/SnO2 heterojunction interface, which broadens the photoresponse range and endows the device with visible-light detection capability. Appropriate annealing treatment can induce esterification and polymerization reactions of pyomelanin molecules, increase the graphitization degree of the pigment layer, further optimize its electrical conductivity and reduce the work function, thereby synergistically optimizing the overall photodetection performance. This study proposes a novel bio-inorganic hybridization strategy combining natural bacterial pigment and traditional semiconductor materials, and provides a low-cost, non-toxic, facile-preparation and high-stability alternative ETL material for high-performance optoelectronic and photodetection devices.
Key words
photodetectors /
SnO2 /
pyomelanin /
bio-hybrid
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Funding
National Natural Science Foundation of China (12564006); Defense Industrial Technology Development Program; Guizhou Provincial Basic Research Program (Grant Nos. MS MS[2026] 300, MS [2026] 296, MS [2025] 203, MS [2025] 206)
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