Abstract
NaSbSe2 has recently shown great potential to be a light-absorber semiconductor in thin-film solar cells. Our first-principles calculations show that NaSbSe2 has a quasi-direct bandgap (1.11 eV indirect vs 1.18 eV direct gap), which is beneficial for increasing the lifetime of minority carriers. The optical absorption coefficient is high (exceeding 10−4 cm−1 for visible light) because of the direct band-edge transition from the (Sb-5s/5p + Se-4p) valence band to (Sb-5p + Se-4p) conduction band. The formation of the dominant acceptor defects such as NaSb, VNa, and VSb makes it difficult to dope NaSbSe2 to n-type, and thus, only the intrinsic p-type conductivity has been observed. Se-rich conditions are found to produce high concentration of hole carriers and low concentration of recombination-center defects, so we propose that the Se-rich conditions should be adopted for fabricating high efficiency NaSbSe2 solar cells. Furthermore, the mixed-anion NaSb(S,Se)2 alloys are predicted to be highly miscible with a low formation enthalpy and a low miscibility temperature (below room temperature), and their bandgaps can be tuned almost linearly from 1.1 to 1.6 eV, covering the optimal bandgap range for single-junction solar cells. Therefore, we propose that alloying provides a promising method for optimizing the performance of NaSbSe2-based solar cells.
Highlights
The search for promising light-absorbing semiconductors has become a very hot topic in the field of high-efficiency solar cells
Experiments show that NaSbS2 has a bandgap of ∼1.5–1.8 eV,20,24 slightly larger than the optimal bandgap (∼1.4 eV)25,26 of the light-absorber in single-junction solar cells
In addition to that Se-rich condition which is in favor of the formation of high carrier concentration, we suggest that the Se-rich condition is needed during the synthesis of NaSbSe2
Summary
The search for promising light-absorbing semiconductors has become a very hot topic in the field of high-efficiency solar cells. Besides CH3NH3PbI3, recent studies reveal that other materials containing partially oxidized post-transition-metal cations, such as In+, Tl+, Pb2+, Sn2+, Sb3+, and Bi3+, have similar lone-pair states and superior photovoltaic properties.. Besides CH3NH3PbI3, recent studies reveal that other materials containing partially oxidized post-transition-metal cations, such as In+, Tl+, Pb2+, Sn2+, Sb3+, and Bi3+, have similar lone-pair states and superior photovoltaic properties.14–19 Among such materials, a novel ternary chalcogenide semiconductor NaSbS2 has attracted increasing attention.. Experiments show that NaSbS2 has a bandgap of ∼1.5–1.8 eV, slightly larger than the optimal bandgap (∼1.4 eV) of the light-absorber in single-junction solar cells. It has a large optical absorption coefficient (104–105 cm−1) for the visible light.. First-principles simulations provide a scitation.org/journal/apm theoretical basis for NaSbS2 being a promising solar cell lightabsorber material.
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