Current challenges and future prospects for a highly efficient (>20%) kesterite CZTS solar cell: A review

CZTS has kesterite structure and the composition's formula is Cu2ZnSn(S/Se)(4). The efficiency of CZTS-Se (Copper-Zinc-Tin-Sulphur-Selenium) solar cell, similar to 12.6%, is much lower than the efficiency of CIGS (Copper-Indium-Gallium-Selenium) solar cell, similar to 22.6%. But the CZTS-Se may be the counterpart of the CIGS and the efficiency may be increased up to 32.2% as theoretically predicted by the Shockley-Queisser (SQ) limit. In solar cell technology, it has been depicted that the efficiency of the solar are affected by the two parameters: (i) variation of the solar insolation and (ii) quality of the materials. Besides this, the narrow phase stability of quaternary phases, unfavorable band alignments, mid-gap states and band tails are main reasons of deficit in the efficiency of kesterite due to the coexistence of the secondary and ternary phases, carrier recombination at the interfaces, defects and series resistances. As a result, the kesterite solar cell has the fluctuated open circuit voltage and the loss of energy. In addition to this, the champion CZTS-Se solar cell is not so environmental friendly because Se is the toxic and the rare earth element. This review provides the vital approaches by discussing the proper materials processing and the appropriate solution to enhance the efficiency of kesterite (CZTS, CZTSe and CZTS/Se) solar cells. Due to the large area quality, high absorption and low-cost materials of the kesterite, it may be used directly in harvesting the solar energy. We have also discussed how to reduce the recombination of the electron-hole pairs by using the interfacial layer so that the efficiency of the kesterite solar cells can be improved.