Charge Transport and Gradient Doping in Nanostructured Polypyrrole Films for Applications in Photocurrent Generation

Author(s)

Pozzoli, Guilherme L. ^{[1, 2]} ; Merces, Leandro ^[1] ; Yassitepe, Emre ^{[1, 3]} ; de Morais, Vitoria B. ^[1] ; de Camargo, Davi H. S. ^{[1, 2]} ; Bufon, Carlos C. Bof ^{[1, 2]}

Affiliation

^[1] Brazilian Ctr Res Energy & Mat CNPEM, Brazilian Nanotechnol Natl Lab LNNano, BR-13083970 Campinas, SP - Brazil

^[2] Sao Paulo State Univ UNESP, Postgrad Program Mat Sci & Technol POSMAT, BR-17033360 Bauru, SP - Brazil

^[3] Fed Univ Maranhao UFMA, Dept Phys CCET, BR-65080805 Sao Luis, Maranhao - Brazil

• Document type: Journal article
• Source: ACS APPLIED NANO MATERIALS; v. 3, n. 3, p. 3060-3070, MAR 2020.
• Web of Science Citations: 0

Abstract

The investigation of the charge-transport mechanism across disordered conducting and semiconducting materials is of relevance, considering the applications in modern organic and hybrid electronics. The transition from bulk to nm-thick layers may lead to unexpected physical/chemical properties as the device interfaces do influence the overall charge-carrier conduction. Here, we present an investigation of the electrical transport across vertical heterojunctions having disordered nm-thick films (polypyrrole, PPy) as the active material. The PPy structures are prepared by chemical polymerization from the pyrrole vapor phase, resulting in film thicknesses of a few tens of nanometers. The electrical characteristics of the devices are evaluated as a function of voltage and temperature, and the charge transport is found to be strongly influenced by the presence of trap states at the PPy highest occupied molecular orbital-giving rise to space-chargelimited conduction with exponential distribution of traps. The trapping-state density is calculated, and X-ray photoelectron spectroscopy revealed an increase of disorder and a reduced doping density at the PPy growth interface. As a proof of concept, the PPy films integrated within the as-fabricated vertical heterostructures are applied as photosensitive devices. The observation of photocurrent is correlated to the presence of a gradient in the doping profile (from ca. 27.6 to 17.2% when thickness decreases from 120 to 20 nm). Our findings contribute to the elucidation of the charge-trapping center's origin in the nm-thick PPy films, as well as envision further applications in photoelectrochemistry, solar cells, and water splitting. (AU)

• FAPESP's process: 18/18136-0 - Hybrid nanodevices: magnetoelectronic transport and development of sensors based on molecules/nanomembranes
• Grantee: Leandro das Mercês Silva
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 14/25979-2 - Fabrication and characterization of devices and systems based on hybrid nanomembranes
• Grantee: Carlos César Bof Bufon
• Support Opportunities: Research Grants - Young Investigators Grants
• FAPESP's process: 14/50906-9 - INCT 2014: in Functional Complex Materials
• Grantee: Fernando Galembeck
• Support Opportunities: Research Projects - Thematic Grants