Design of solar cell materials via soft X-ray spectroscopy

• Published in: Journal of electron spectroscopy and related phenomena Vol. 190; pp. 2 - 11
• Main Authors: Himpsel, F.J., Cook, P.L., de la Torre, G., Garcia-Lastra, J.M., Gonzalez-Moreno, R., Guo, J.-H., Hamers, R.J., Kronawitter, C.X., Johnson, P.S., Ortega, J.E., Pickup, D., Ragoussi, M.-E., Rogero, C., Rubio, A., Ruther, R.E., Vayssieres, L., Yang, W., Zegkinoglou, I.
• Format: Journal Article
• Language: English; French; German
• Published: Elsevier B.V 01.10.2013
• Subjects: Band offset; Design engineering; Devices; Diamond; Dye molecule; Dyes; Photovoltaic cells; Photovoltaics; Porphyrins; Soft x-rays; Solar cell; Solar cells; Spectroscopy; X-ray absorption spectroscopy; Solar cell; Diamond; X-ray absorption spectroscopy; Band offset; Dye molecule; Photovoltaics
• ISSN: 0368-2048; 1873-2526
• DOI: 10.1016/j.elspec.2012.10.002

► The use of soft X-ray spectroscopy for developing new materials for solar cells is illustrated. ► A generic layout of a solar cell is given, which facilitates the discussion of the energy levels involved in a solar cell and their optimization. ► Systematic measurements of organometallic dyes are presented in combination with density functional theory. ► The data reveal trends that are useful for tailoring materials for solar cells. ► A solar cell design based on thin film p-type diamond as donor is used as example. This overview illustrates how spectroscopy with soft X-rays can assist the development of new materials and new designs for solar cells. The starting point is the general layout of a solar cell, which consists of a light absorber sandwiched between an electron donor and an electron acceptor. There are four relevant energy levels that can be measured with a combination of X-ray absorption spectroscopy and photoelectron spectroscopy, as illustrated for an organic dye as absorber attached to a p-doped diamond film as donor. Systematic measurements of organometallic dyes (phthalocyanines and porphyrins) as a function of the metal atom are presented for the metal 2p and N 1s absorption edges. In combination with density functional theory one can discern trends that are useful for tailoring absorber molecules. A customized porphyrin molecule is investigated that combines an absorber with a donor and a linker to an oxide acceptor. The bridge to device fabrication is crossed by correlating spectroscopic features with the photocurrent in hematite photoanodes for water splitting. For speeding up the development of new materials and designs of solar cells a feedback loop between spectroscopy, theory, synthesis and device fabrication is envisioned.