Carbon Nanotubes for Quantum Dot Photovoltaics with Enhanced Light Management and Charge Transport

Journal Article · Thu Nov 08 00:00:00 EST 2018 · ACS Photonics

DOI:https://doi.org/10.1021/acsphotonics.8b00982· OSTI ID:1489327

Tazawa, Yujiro ^[1]; Habisreutinger, Severin N. ^[2]; Zhang, Nanlin ^[1]; Gregory, Daniel A. F. ^[1]; Nagamine, Gabriel ^[3]; Kesava, Sameer V. ^[1]; Mazzotta, Giulio ^[1]; Assender, Hazel E. ^[1]; Riede, Moritz ^[1]; Padilha, Lazaro A. ^[3]; Nicholas, Robin J. ^[1]; Watt, Andrew A. R. ^[1]

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1. Univ. of Oxford (United Kingdom)
2. Univ. of Oxford (United Kingdom); National Renewable Energy Lab. (NREL), Golden, CO (United States)
3. Universidade Estadual de Campinas, Rua Sérgio Buarque de Holanda (Brazil)

Colloidal quantum dot (CQD)-based photovoltaics are an emerging low-cost solar cell technology with power conversion efficiencies exceeding 10%, i.e., high enough to be interesting for commercialization. Well-controlled and understood charge carrier transport through the device stack is required to make the next step in efficiency improvements. In this work, polymer-wrapped single-walled carbon nanotube (SWNT) films embedded in an insulating poly(methyl methacrylate) (PMMA) matrix and capped by a thermally evaporated Au electrode are investigated as a composite hole transport layer and optical spacer. Employing transient absorption spectroscopy we show that the SWNTs enhance the charge transfer rate from CQD to CQD, ZnO, or SWNT. In order to pinpoint the underlying mechanism for the improvement, we investigate the energetics of the junction by measuring the relative alignment of the band edges, using Kelvin probe and cyclic voltammetry. Measuring the external quantum efficiency and absorption we find that the improvement is not mainly from electronic improvements but from enhanced absorption of the CQD absorber. We demonstrate experimentally and theoretically, by employing a transfer-matrix model, that the transparent PMMA matrix acts as an optical spacer, which leads to an enhanced absorption in the absorber layer. Lastly, with these electronic and optical enhancements, the efficiency of the PbS CQD solar cells improved from 4.0% to 6.0%.

• Research Organization: National Renewable Energy Lab. (NREL), Golden, CO (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE)
• Grant/Contract Number: AC36-08GO28308
• OSTI ID: 1489327
• Report Number(s): NREL/JA-5900-73019
• Journal Information: ACS Photonics, Vol. 5, Issue 12; ISSN 2330-4022
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
36 MATERIALS SCIENCE
charge carrier transfer
colloidal quantum dots
hole transport layer
optical spacer effect
photovoltaics
single-walled carbon nanotube