Experimental and Theoretical Study into Interface Structure and Band Alignment of the Cu2Zn1- x Cd x SnS4 Heterointerface for Photovoltaic Applications

Sachin R Rondiya; Yogesh Jadhav; Nelson Y Dzade; Raihan Ahammed; Tanmay Goswami; Abir De Sarkar; Sandesh Jadkar; Santosh Haram; Hirendra N Ghosh

doi:10.1021/acsaem.9b02314

Experimental and Theoretical Study into Interface Structure and Band Alignment of the Cu₂Zn_{1- x} Cd _x SnS₄ Heterointerface for Photovoltaic Applications

ACS Appl Energy Mater. 2020 Jun 22;3(6):5153-5162. doi: 10.1021/acsaem.9b02314. Epub 2020 May 5.

Authors

Sachin R Rondiya¹, Yogesh Jadhav², Nelson Y Dzade³, Raihan Ahammed¹, Tanmay Goswami¹, Abir De Sarkar¹, Sandesh Jadkar⁴, Santosh Haram², Hirendra N Ghosh¹

Affiliations

¹ Institute of Nano Science and Technology, Mohali, Punjab 160062, India.
² Department of Chemistry, Savitribai Phule Pune University, Pune 411007, India.
³ School of Chemistry, Cardiff University, Cardiff, CF10 3AT, Wales United Kingdom.
⁴ Department of Physics, Savitribai Phule Pune University, Pune 411007, India.

Abstract

To improve the constraints of kesterite Cu₂ZnSnS₄ (CZTS) solar cell, such as undesirable band alignment at p-n interfaces, bandgap tuning, and fast carrier recombination, cadmium (Cd) is introduced into CZTS nanocrystals forming Cu₂Zn_1-x Cd _x SnS₄ through cost-effective solution-based method without postannealing or sulfurization treatments. A synergetic experimental-theoretical approach was employed to characterize and assess the optoelectronic properties of Cu₂Zn_1-x Cd _x SnS₄ materials. Tunable direct band gap energy ranging from 1.51 to 1.03 eV with high absorption coefficient was demonstrated for the Cu₂Zn_1-x Cd _x SnS₄ nanocrystals with changing Zn/Cd ratio. Such bandgap engineering in Cu₂Zn_1-x Cd _x SnS₄ helps in effective carrier separation at interface. Ultrafast spectroscopy reveals a longer lifetime and efficient separation of photoexcited charge carriers in Cu₂CdSnS₄ (CCTS) nanocrystals compared to that of CZTS. We found that there exists a type-II staggered band alignment at the CZTS (CCTS)/CdS interface, from cyclic voltammetric (CV) measurements, corroborated by first-principles density functional theory (DFT) calculations, predicting smaller conduction band offset (CBO) at the CCTS/CdS interface as compared to the CZTS/CdS interface. These results point toward efficient separation of photoexcited carriers across the p-n junction in the ultrafast time scale and highlight a route to improve device performances.