Crystal engineering and thin-film deposition strategies towards improving the performance of kesterite photovoltaic cell

With high absorption coefficient (104 cm−1), optimal bandgap (~1.5 eV), low toxicity and the abundance of its constituent elements, kesterite (Cu2ZnSnS4 or CZTS) displays the properties of an ideal photovoltaic material. Kesterite is structurally analogous to chalcopyrite (Cu2InGaS2 or CIGS) and can thus be produced through the already established techniques for the synthesis of commercial CIGS. Though CIGS- and CdTe-based thin-film solar cells have attained levels of power efficiency values (up to ~22%) that compare with that of crystalline silicon-based wafer solar cell, they contain rare earth elements (indium, tellurium and Cd) that are toxic. This article reviews the crystal structure formation and properties of CZTS. Material synthesis, thin-film deposition methodologies and different layers that have been developed for kesterite-based photovoltaic (PV) cell are reported. Factors that hinder high-power conversion efficiency, including large open-circuit voltage deficit (Voc,def), are discussed. Strategies, such as alloy formation, which have been employed to overcome the limitations of using kesterite in PV cell applications are presented, together with the future direction in the quest for improving the performance of kesterite PV cell devices.