(Li,Na)SbS2 as a promising solar absorber material: A theoretical investigation

NaSbS2 has been proposed as a novel photovoltaic material, but its band gap is not suitable for single-junction solar cells. In the present study, the systematic first-principles calculations were carried out to investigate the structural, mechanical, electronic and optical properties of ASbS2 (A = Li, Na, K) and Na1-xLixSbS2 solid solutions. These structures show good structural stability compared to CH3NH3PbI3. The results indicate that all the structures are indirect band gap semiconductors. The band gap of ASbS2 increases gradually when the alkali metal changes from Li to K. The band gap of NaSbS2 can be tuned by manipulating the amount of Li doping. The Na1-xLixSbS2 solid solutions have suitable band gaps for light-absorber semiconductors in solar cells. Moreover, the suitable band gap of NaSbS2 can be also obtained under moderate pressure. The mechanical properties of these materials are also analyzed, and the results indicate that they are brittle materials except for KSbS2. The optical absorption coefficients of these compounds are large over 10−5 cm−1 in the visible light region. We find that alloying can provide a feasible and effective approach for improving the photovoltaic performance of NaSbS2-based solar cells.