Energy level alignment and nanoscale investigation of a-TiO2/Cu-Zn-Sn-S interface for alternative electron transport layer in earth abundant Cu-Zn-Sn-S solar cells

Nisika, Kulwinder Kaur, Kanika Arora, Ashraful Haider Chowdhury, Behzad Bahrami, Qiquan Qiao, Mukesh Kumar

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


Efficiency of earth abundant and pure sulfide kesterite Cu-Zn-Sn-S (CZTS) solar cell has been stagnant around 9.4% for years, while its counterpart Cu-In-Ga-Se (CIGS) reports an efficiency of more than 22%. Low open circuit voltage (VOC) is the major challenging factor for low efficiency due to severe nonradiative interface recombinations. The existence of higher defect states at the conventional CZTS-CdS interface due to undesirable energy level alignment and lattice misfit promotes trap-assisted recombinations and results in low VOC. In this work, amorphous TiO2 (E g = 3.8 eV) is proposed as a promising substitute to the conventional and low bandgap CdS (E g = 2.4 eV) layer. The surface and interface of the CZTS-TiO2 layer were investigated using X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The result reveals favorable "spike"-like conformations at the CZTS-TiO2 interface with a conduction band offset value of 0.17 eV. The nanoscale probing of the interface by Kelvin probe force microscopy across CZTS-TiO2 layers shows a higher potential barrier for interface recombination at CZTS-TiO2 in contrast to the conventional CZTS-CdS interface. Finally, the fast decay response and lower persistent photoconductivity of photogenerated carriers for CZTS-TiO2 heterojunction based photodetectors further validate our results. The energy level alignment and nanoscale interface studies signify TiO2 as a promising alternate buffer layer for earth abundant CZTS solar cells.

Original languageEnglish (US)
Article number193104
JournalJournal of Applied Physics
Issue number19
StatePublished - Nov 21 2019
Externally publishedYes

ASJC Scopus subject areas

  • Physics and Astronomy(all)


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