This journal is c The Royal Society of Chemistry 2013 Chem. Soc. Rev. Cite this: DOI: 10.1039/c3cs60054h Nanochemistry and nanomaterials for photovoltaics Guanying Chen, ab Jangwon Seo,w b Chunhui Yang* a and Paras N. Prasad* bc Nanochemistry and nanomaterials provide numerous opportunities for a new generation of photo- voltaics with high solar energy conversion efficiencies at low fabrication cost. Quantum-confined nanomaterials and polymer–inorganic nanocomposites can be tailored to harvest sun light over a broad range of the spectrum, while plasmonic structures offer effective ways to reduce the thickness of light- absorbing layers. Multiple exciton generation, singlet exciton fission, photon down-conversion, and photon up-conversion realized in nanostructures, create significant interest for harvesting underutilized ultraviolet and currently unutilized infrared photons. Nanochemical interface engineering of nanoparticle surfaces and junction-interfaces enable enhanced charge separation and collection. In this review, we survey these recent advances employed to introduce new concepts for improving the solar energy conver- sion efficiency, and reduce the device fabrication cost in photovoltaic technologies. The review concludes with a summary of contributions already made by nanochemistry. It then describes the challenges and opportunities in photovoltaics where the chemical community can play a vital role. A. Background A1. Introduction Meeting ever-growing energy needs is one of the important challenges of the twenty-first century. Fossil fuels (coal, oil and natural gas) provide energy sources for our needs now; how- ever, they will run out of stock considering the high consump- tion rate. 1,2 Power generation through burning fossil fuels also raises a significant concern of damage to environment, as large amounts of carbon dioxide and sulfur dioxide are released in the burning process. 1,2 A quest for new alternative renewable energy sources is urgent and necessary. There are about one hundred and twenty thousand terawatts of solar power irradiating earth. Globally, humans consume only fifteen terawatts. 3 Harnessing solar energy through photo- voltaic (PV) technology has the potential to provide a virtually unlimited supply of usable energy that is sustainable and environmentally benign in operation. 4–10 However, economical implementation of PV technology on a global scale requires critical advances in both materials and devices to decrease the cost and increase the power conversion efficiency. 11–14 Nano- chemistry and nanomaterials open up new opportunities to achieve higher solar energy conversion efficiencies at lower fabrication costs, as they allow the use of inexpensive materials and inexpensive processing technologies to harvest sunlight by efficiently capturing photon energy over a broad spectral range, and then quickly separating and collecting photo-generated charge carriers. 15–22 Spectral tuning in semiconductor quantum- confined nanomaterials, 23 sensitizing dyes, 14 and polymers, 18,20 allows the band-gap of a single-junction device to be optimally matched over a broad range of the solar spectrum to efficiently produce photon-generated charge carriers. It also allows fabri- cation of tandem or multi-junction solar cells which sequen- tially harvest the Sun’s constituent spectral components in tandem, 24,25 accomplishing power-conversion efficiencies potentially up to 68% through a significant reduction of losses associated with intra-band relaxations. 3 Nanochemistry can be utilized to tailor numerous nanointerfaces in these solution- processed nanostructured PV cells, which provides great oppor- tunity to enable efficient photo-induced charge separation and produce significantly improved charge transport and collec- tion. Multi-exciton generation, 26 singlet exciton fission, 27 plasmonic-induced light trapping, 16,17 as well as photon up-conversion and down-conversion, 28–30 realized in nano- structures, provide a range of novel approaches to harvest underutilized ultraviolet and currently unutilized infrared (IR) photons with high efficiencies, breaking the Shockley–Queisser limit set for a single junction solar device. 31 In addition, a School of Chemical Engineering and Technology, Harbin Institute of Technology, Harbin, Heilongjiang 150001, People’s Republic of China. E-mail: yangchh@hit.edu.cn b Department of Chemistry and the Institute for Lasers, Photonics, and Biophotonics, University at Buffalo, State University of New York, Buffalo, New York 14260, United States. E-mail: pnprasad@buffalo.edu c Department of Chemistry, Korea University, Seoul 136-701, Korea † Present address: Center for Supramolecular Optoelectronic Materials, Department of Materials Science and Engineering, Seoul National University, Seoul 151-744, Korea. Received 7th February 2013 DOI: 10.1039/c3cs60054h www.rsc.org/csr Chem Soc Rev REVIEW ARTICLE Published on 18 July 2013. Downloaded by University at Buffalo Libraries on 18/07/2013 23:16:07. View Article Online View Journal