Nanocarbon-Based Photovoltaics

Abstract

Carbon materials are excellent candidates for photovoltaic solar cells: they are Earth-abundant, possess high optical absorption, and maintain superior thermal and photostability. Here we report on solar cells with active layers made solely of carbon nanomaterials that present the same advantages of conjugated polymer-based solar cells, namely, solution processable, potentially flexible, and chemically tunable, but with increased photostability and the possibility to revert photodegradation. The device active layer composition is optimized using ab initio density functional theory calculations to predict type-II band alignment and Schottky barrier formation. The best device fabricated is composed of PC(70)BM fullerene, semiconducting single-walled carbon nanotubes, and reduced graphene oxide. This active-layer composition achieves a power conversion efficiency of 1.3%-a record for solar cells based on carbon as the active material-and we calculate efficiency limits of up to 13% for the devices fabricated in this work, comparable to those predicted for polymer solar cells employing PCBM as the acceptor. There is great promise for improving carbon-based solar cells considering the novelty of this type of device, the high photostability, and the availability of a large number of carbon materials with yet untapped potential for photovoltaics. Our results indicate a new strategy for efficient carbon-based, solution-processable, thin film, photostable solar cells.

Structure-property relations in amorphous carbon for photovoltaics

“…[1][2][3][4] Carbon nanomaterials, such as nanotubes, graphene, fullerenes, and their chemical derivatives, possess a range of favorable properties for PV. For example, thin films of carbon nanomaterials manufactured from solution can absorb a significant fraction of incident sunlight, while possessing chemical and thermal stability.…”

“…For example, thin films of carbon nanomaterials manufactured from solution can absorb a significant fraction of incident sunlight, while possessing chemical and thermal stability. 2,5 Despite these advantages, carbon nanomaterials require precisely controlled structures to be employed in solar cells. For example, recent work has shown that carbon nanotubes with specific diameters and chiralities are necessary to optimize PV devices based on nanotubes and fullerenes;…”

Graphene Derivatives: Controlled Properties, Nanocomposites, and Energy Harvesting Applications

“…As expected, graphene and graphene oxide-based materials have also been used in the active layer of the OPVs, combined with P3HT: PCBM, obtaining a maximum PCE of 1.046% [28] or even without any polymer, only using PCBM/rGO/SWCNTs as active layer, obtaining a PCE of 1.3%, but with a significant improvement in thermal stability and resistance to aging by atmosphere with oxygen [29].…”

Computer calculations across time and length scales in photovoltaic solar cells

“…For the ideal case of a sunlight pulse absorbed by Si, a pocket of excited (so-called hot) electrons is generated in the conduction band spanning a 2 eV range above the CBM. 11 Similar considerations apply to excited holes formed with a distribution of energies below the VBM. The surplus energy, given by the difference between the electron or hole energy and the conduction or valence band edge, respectively, is rapidly lost through sub-ps inelastic electron-phonon and electron-electron scattering processes.…”