ABSTRACT
Photoinduced energy conversion processes are at the center of many green and renewable energy technologies.1−7 Materials widely used for photo-energy conversion are classic semiconductors, especially those at the nanoscale, such as silicon nanoparticles, semiconductor quantum dots (QDs), or nanorods.3,4,8−15 Since the discovery of fullerenes,16 carbon nanomaterials have been widely pursued for their photon-harvesting and photoinduced redox characteristics relevant to energy conversion applications.17−20 In fact, fullerene derivatives are among the most popular materials used in organic or related photovoltaic devices.21−27
Carbon nanotubes (CNTs) are also photoactive, with high optical absorption cross-sections (for both one-and multiphoton excitations),28−31 rich excited state properties,32−36 and efcient photoinduced charge-transfer processes.35,37,38 CNTs have been investigated extensively for potential applications in photo-energy conversions.39−42 For example, CNTs have been integrated successfully into organic photovoltaic devices as part of the photoactive layer, and as highly prospective materials to replace counter electrodes and transparent conductive oxide (TCO) layers. The rst use of CNTs as electron acceptors in bulk-heterojunction solar cells was reported in 2002, when researchers blended single-walled carbon nanotubes (SWCNTs) with polythiophenes and observed an increase in the photocurrent by two orders of magnitude.43 In another report, the use of CNTs in dye-sensitized solar cells (DSSCs) has doubled the efciency of such photoelectrochemical solar cells.44 It has also
16.1 Introduction ..........................................................................................................................463 16.2 Optical Absorption ...............................................................................................................464 16.3 Photoexcited State Properties ............................................................................................... 467
16.3.1 Photoluminescence Emissions .................................................................................. 467 16.3.2 Charge Separation and Transfers .............................................................................. 471
16.4 Photoinduced Energy Conversion ......................................................................................... 475 16.4.1 CNTs in Photocatalytic Water Splitting and CO2 Conversion .................................. 475 16.4.2 CNTs in Solar Cells .................................................................................................. 478
16.4.2.1 CNTs in Bulk Heterojunction ....................................................................480 16.4.2.2 CNTs in Dye-Sensitized Solar Cells .......................................................... 483 16.4.2.3 CNTs in Transparent Electrodes ................................................................488
