Author:       2014-09-04

Because of energy shortage and environmental pollution, there is a growing research interest on solar cells aiming at exploiting solar energy with high efficiency and low cost. The current mainstream thin film solar cells, cadmium telluride (CdTe) and copper indium gallium selenide (CIGS), possess the advantages of high energy conversion efficiency, low cost, light weight and flexibility and have received widespread application. However, the toxicitity of Cd, and the elemental scarcity of Te, In and Ga raw materials restrict terawatt scale deployment of these technologies. Seeking earth-abundant, low-toxicity, low-cost materials for ef?cient solar cells is a long-standing goal for solar cell researchers.

Sb2Se3 is a very promising absorber material for thin film photovoltaics: i) Sb2Se3 has a direct band gap of 1.15 eV, very close to Si (1.12 eV) and hence the solar conversion efficiency limit for single-junction Sb2Se3 solar cell is >30%; ii) Sb2Se3 is a binary compound with fixed phase. Also, Sb2Se3 thin film could be grown at relatively low temperature (<300℃), reducing manufacturing energy consumption; iii) The constituents of Sb2Se3 is low cost (Sb and Cu has similar price, and Se is around 390 RMB/kg), earth-abundant and green (neither China nor US and EU list Sb2Seas highly toxic or carcinogenic); iv) Research on Sb2Se3 is very rare; only until Dec. 2013 is there a first report on Sb2Se3 based solar cells. In this sense, Sb2Se3 has very attractive material and optoelectronic properties, promising the fabrication of high-efficiency, low-cost thin film photovoltaics.

Prof. Jiang Tang’s group at Wuhan National Laboratory for Optoelectronics has focused on Sb2Se3 solar cells and achieved some research progress:

i)  Ying Zhou et. al. first dissolved elemental antimony and selenium into hydrazine to obtain a stable precursor solution, fabricated Sb2Se3 thin films through spin-coating and thermal annealing, and further studied the band structure, fluorescence, doping density, carrier mobility and other basic physical and optical properties of Sb2Se3. They also built a Sb2Se3/TiO2 heterojunction thin film solar cells and obtained a solar conversion efficiency of 2.26 % (for full details, please refer to http://onlinelibrary.wiley.com/doi/10.1002/

aenm.201301846)

ii)  By taking advantage of high vapor pressure of Sb2Se3, Xinsheng Liu and Jie Chen et. al. produced Sb2Se3 thin films through thermal evaporation. Through careful optimization, as-prepared Sb2Se3 thin films demonstrated excellent optical and electronic properties. Furthermore, they built a substrate FTO/Sb2Se3/CdS/ZnO/ZnO:Al/Au solar cells and achieved  a 2.1% device efficiency (please refer to http://pubs.acs.org/doi/abs/10.1021/

am502427s)

  iii) Meanwhile, Miao Luo et. al. prepared superstrate CdS/Sb2Se3 solar cells also employing thermally evaporated Sb2Se3film and got a 1.9% conversion efficiency. As-prepared device showed excellent storage stability and light stability. They further applied a comprehensive analysis on device physics revealing the CdS/Sb2Se3 junction quality and the doping profile in the Sb2Seabsorber. Last they also analyzed the limiting factor in their devices (for details please refer to http://scitation.aip.org/content/aip/journal/apl/104/17/10.1063/

1.4874878).

  iv) Very recently, Meiying Leng et. al. introduced an additional selenization step to anneal the thermally evaporated Sb2Se3 absorber layer. In such a way the selenium vacancy (VSe), a detrimental recombination center in Sb2Se3, could be largely suppressed and thus resulted in a superstrate CdS/Sb2Se3 having device efficiency of 3.7%. They further applied biased external quantum efficiency and photoresponse study to uncover the selenization mechanism in detail (please refer to http://scitation.aip.org/content/aip/journal/apl/105/8/

10.1063/1.4894170)

These work are financially supported by the “National 1000 Young Talents” project, the National Natural Science Foundation of China (61274055, 61322401), the seed project of WNLO, the Fundamental Research Funds for the Central Universities, HUST (0118187043), and China Postdoctoral Science Foundation (2013M542015).