The Role of Sodium as a Surfactant and Suppressor of Non‐Radiative Recombination at Internal Surfaces in Cu₂ZnSnS₄

Abstract

It is well‐known that sodium improves the performance of Cu2ZnSnS4 (CZTS) devices, yet the mechanism of the enhancement is still not fully understood. This work aims to present a unified account of the relationships between grain boundaries in CZTS, sodium content at these boundaries, non‐radiative recombination, and surfactant effects that produce large microstructural changes. Using temperature‐dependent photoluminescence measurements, it is demonstrated that samples containing dramatically different grain sizes display identical radiative and non‐radiative decay characteristics when sufficient sodium is present in the film. It is also shown that the sodium concentration needed to efficiently passivate non‐radiative defects is significantly less that the quantity needed to obtain micrometer‐sized CZTS grains. Finally, the high densities of donor‐acceptor pairs that are observed in CZTS films appear to reside within the grains themselves, rather than at grain boundaries.

Photocatalysis: Basic Principles, Diverse Forms of Implementations and Emerging Scientific Opportunities

“…[24c,42] The recombination dissipates the harvested energy in the form of heat (nonradiative recombination) or light emission (radiative recombination). [43] The long-lived photogenerated charges on the surface have the potential to promote different redox reactions, the details of which depend on the donor or acceptor properties of the surface absorbed species.…”

Opposing effects of stacking faults and antisite domain boundaries on the conduction band edge in kesterite quaternary semiconductors

“…Since current thin-film technologies mostly rely on polycrystalline materials, physical properties of extended defects, especially grain boundaries (GBs) have been investigated to understand their effects on the device efficiency [10][11][12][13][14][15][16]. Other extended defects like stacking faults (SFs) and antisite domain boundaries (ADBs) have been less documented as compared to the GBs, but since SFs in CdTe act as electron barriers and reduce the efficiency [17][18][19][20], SFs in CZTS should be investigated.…”

Complex Interplay between Absorber Composition and Alkali Doping in High‐Efficiency Kesterite Solar Cells

“…So far the most research attention has been paid to sodium, resulting in many thorough investigations which revealed grain size enhancement, passivation of grain boundaries, and an increase in net hole concentration as the major beneficial effects of sodium treatments. [3][4][5][6] Also lithium addition has shown to improve device performance by boosting the electronic quality of the CZTSSe absorber material and grain boundaries. [7] First studies on the effect of potassium addition confirmed advantageous effects on kesterite absorber growth and optoelectronic properties similar to Na.…”

“…[3][4][5][6] Also lithium addition has shown to improve device performance by boosting the electronic quality of the CZTSSe absorber material and grain boundaries. [7] First studies on the effect of potassium addition confirmed advantageous effects on kesterite absorber growth and optoelectronic properties similar to Na.…”