The path towards a high-performance solution-processed kesterite solar cell ☆

A power conversion efficiency record of 10.1% was achieved for kesterite absorbers, using a Cu2ZnSn(Se,S)4 thin-film solar cell made by hydrazine-based solution processing. Key device characteristics were compiled, including light/dark J–V, quantum efficiency, temperature dependence of Voc and series resistance, photoluminescence, and capacitance spectroscopy, providing important insight into how the devices compare with high-performance Cu(In,Ga)Se2. The record kesterite device was shown to be primarily limited by interface recombination, minority carrier lifetime, and series resistance. The new level of device performance points to the significant promise of the kesterites as an emerging and commercially interesting thin-film technology. Copyright © 2011 John Wiley & Sons, Ltd.

Device characteristics of a 10.1% hydrazine-processed Cu2ZnSn(Se,S)4 solar cell

Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) based solar cells are promising candidates for low cost solar cells due to the natural abundance and low toxicity of the constituent elements. Here, we present the first reported synthesis of colloidal CZTS nanocrystals using a simple solution-phase method. Solar cells fabricated using selenized CZTS nanocrystal inks had a power conversion efficiency of 0.74% under AM1.5G illumination.

Synthesis of Cu2ZnSnS4 Nanocrystal Ink and Its Use for Solar Cells

Kesterite materials (Cu2ZnSn(S,Se)4) are made from non-toxic, earth-abundant and low-cost raw materials. We summarise here the structural and electronic material data relevant for the solar cells. The equilibrium structure of both Cu2ZnSnS4 and Cu2ZnSnSe4 is the kesterite structure. However, the stannite structure has only a slightly lower binding energy. Because the band gap of the stannite is predicted to be about 100 meV lower than the kesterite band gap, any admixture of stannite will hurt the solar cells. The band gaps of Cu2ZnSnS4 and Cu2ZnSnSe4 are 1.5 and 1.0 eV, respectively. Hardly any experiments on defects are available. Theoretically, the CuZn antisite acceptor is predicted as the most probable defect. The existence region of the kesterite phase is smaller compared with that of chalcopyrites. This makes secondary phases a serious challenge in the development of solar cells. Copyright © 2012 John Wiley & Sons, Ltd.

Nobuyuki Sasaguchi

Papers

Preparation and evaluation of Cu2ZnSnS4 thin films by sulfurization of EB evaporated precursors