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

Abstract

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 paper, 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. With these electronic and optical enhancements, the efficiency of the PbS CQD solar cells improved from 4.0% to 6.0%.

Improving Charge Collection from Colloidal Quantum Dot Photovoltaics by Single-Walled Carbon Nanotube Incorporation

“…For example, Ihly et al demonstrated a remarkable performance enhancement of perovskite solar cell by introducing a SWNT interlayer between the perovskite layer and the HTL, which was attributed to the rapid hole extraction from the absorber layer with extremely slow back-transfer/recombination . In addition, Tazawa et al applied poly­(3-hexylthiophene-2,5-diyl)-wrapped SWNT to the CQDPV by embedding the composites into the poly­(methyl methacrylate) matrix, serving as a HTL, and observed significantly improved J SC owing to the fast carrier transfer . Both reports suggest that the SWNT incorporation into a solar cell can render lossless charge-transporting behavior within the device, resulting in improved charge carrier collection and, consequently, enhanced solar cell performance.…”

“…36 In addition, Tazawa et al applied poly(3-hexylthiophene-2,5-diyl)-wrapped SWNT to the CQDPV by embedding the composites into the poly(methyl methacrylate) matrix, serving as a HTL, and observed significantly improved J SC owing to the fast carrier transfer. 37 Both reports suggest that the SWNT incorporation into a solar cell can render lossless charge-transporting behavior within the device, resulting in improved charge carrier collection and, consequently, enhanced solar cell performance. Also, another report suggested that improved stability in air could be achieved by introducing a semiconducting SWNT interlayer below the Au electrode.…”

Critical Review on Interrelationship of Electro-Devices in PV Solar Systems with Their Evolution and Future Prospects for MPPT Applications

“…Green disposal at the end of the product lifecycle is also conceivable, as nanomaterial-based solar cells have the potential to be made entirely of carbon through rigorous separation, purification, and enrichment methods that guarantee the inherent properties of pure carbon at ideal levels [104]. Fourth-generation: nano photovoltaic Graphene-silicon 18.8% [87] 0-1 TBD TBD TBD Graphene-quantum dot 13.7% [88] Graphene-perovskite 16.1% [89] Graphene/perovskitequantum dot 17.9% [90] Graphene/quantum dot-perovskite 19.8% [91] Graphene-DSSC 11.5% [92] Carbon nanotubes-silicon 20.1% [93] Carbon nanotubes-quantum dot 6.00% [94] Carbon nanotubes-perovskite 37.4% [95] Carbon nanotubes-DSSC 10.3% [96] Graphene/carbon nanotubes-silicon 17.5% [97] Carbon nanotubes/graphenequantum dot 8.28% [98] Carbon nanotubes/silicon/graphenequantum dot 14.9% [99] Graphene/carbon nanotubes-perovskite 19.6% [100] Carbon nanotubes/graphene-DSSC 8.34% [101] These organic nanomaterials are also highly flexible as they can take on other forms of structure [105]. With their flexibility, scientists have created a variety of solar cells that silicon cannot produce.…”