Design of Lead-Free and Stable Two-Dimensional Dion–Jacobson-Type Chalcogenide Perovskite A′La₂B₃S₁₀ (A′ = Ba/Sr/Ca; B = Hf/Zr) with Optimal Band Gap, Strong Optical Absorption, and High Efficiency for Photovoltaics

Searching for energetic photovoltaic absorbers is a favorable solution to the current energy crisis. As a star material for solar cells, MAPbI3 (MA = CH3NH3) has a suitable band gap, strong optical absorption, great defect tolerance, and high certified power conversion efficiency (PCE) up to 25.2%. However, the lead toxicity and poor long-term stability limit its application in photovoltaic devices. To break through these bottlenecks, we design two-dimensional (2D) Dion–Jacobson (DJ)-type (n = 3) chalcogenide perovskites A′La2B3S10 (A′ = Ba, Sr, Ca; B = Hf, Zr), with optimal band gap, strong optical absorption, high carrier mobility, and excellent optoelectronic properties, based on the powerful first-principles and advanced HSE06 calculations. Especially, we find that, superior to MAPbI3, 2D A′La2B3S10 perovskites have the following several outstanding properties. (1) They are Pb-free and environmentally friendly. (2) The structural stability is better than that of MAPbI3. (3) The direct band gap (∼1.33 eV of BaLa2Hf3S10), i.e., the optimal value of the SQ limit, is more suitable than that of MAPbI3 (∼1.55 eV) with a 0.22 eV energy-loss spectrum. (4) The carrier mobility (1.8–2.6 × 103 cm2 V–1 s–1) is larger than that of MAPbI3 (∼37 cm2 V–1 s–1). (5) The optical absorption (∼6 × 105 cm–1) in the visible range is three times stronger than that of MAPbI3 (∼2 × 105 cm–1). (6) The estimated PCE (∼30.9% in BaLa2Hf3S10) is higher than that of MAPbI3 (∼30%). These amazing characteristics indicate that 2D A′La2B3S10 perovskites are promising absorbers for photovoltaics.