Mixed Two-Dimensional Organic-Inorganic Halide Perovskites for Highly Efficient and Stable Photovoltaic Application

Abstract

Solar cells made of hybrid organic-inorganic perovskite (HOIP) materials have attracted ever-increasing attention due to their high efficiency and easy fabrication. However, issues regarding their poor stability remain a challenge for practical applications. Engineering the composition and structure of HOIP can effectively enhance the thermal stability and improve the power conversion efficiency (PCE). In this work, mixed two-dimensional (2D) HOIPs are systematically investigated for solar-power harvesting using first-principles calculations. We find that their electronic properties depend strongly on the mixed atoms (Cs, Rb, Ge and Pb) and the formation energy is related to the HOIP's composition, where the atoms are more easily mixed in SnI-2D-HOIPs due to low formation energy at the same composition ratio. We further show that optimal solar energy harvesting can be achieved on the solar cells composed of mixed SnI-2D-HOIPs because of reduced bandgaps, enhanced mobility and improved stability. Importantly, we find that the mixed atoms (Cs, Rb, Ge and Pb) with the appropriate composition ratios can effectively enhance the solar-to-power efficiency and show greatly improved resistance to moisture. The findings demonstrate that mixed 2D-HOIPs can replace the bulk HOIPs or pure 2D-HOIPs for applications into solar cells with high efficiency and stability.

Keywords: effective mass; electronic properties; first-principles calculation; mixed 2D HOIPs; solar-energy harvesting; stability.

Figure 1

(a) Optimized structures of BA₂MA₂B₃X₁₀ (B = Pb²⁺ or Sn²⁺; X = Br⁻ or I⁻) with the mixed Cs/Rb atoms. (b) Relaxed structures of BA₂MA₂Sn₃I₁₀ with the mixed Ge/Pb atoms. Sn/Pb = silver gray; Cs/Rb = purple; Ge/Pb = green; I/Br = bronze; N = blue; C = gray; H = white.

Figure 2

Formation energies of BA₂MA₂B₃X₁₀ (B = Pb²⁺ or Sn²⁺; X = Br⁻ or I⁻) mixed with (a) Cs atom and (b) Rb atom. (c) Formation energy of BA₂MA₂Sn₃I₁₀ mixed with the Ge or Pb atom.

Figure 3

Bandgaps of BA₂MA₂B₃X₁₀ (B = Pb²⁺ or Sn²⁺; X = Br⁻ or I⁻) mixed with (a) Cs atom and (b) Rb atom. (c) Bandgaps of BA₂MA₂Sn₃I₁₀ mixed with Ge or Pb atom.

Figure 4

Carrier effective mass for 2D-HOIPs by mixing Cs/Rb atom at different concentrations (0%, 25%, 50%, 75% and 100%): (a) SnI-2D-HOIPs, (b) PbI-2D-HOIPs, (c) SnBr-2D-HOIPs, and (d) PbBr-2D-HOIPs.

Figure 5

Carrier effective mass for 2D-HOIPs by mixing Ge/Pb atom at different concentrations (0%, 25%, 50%, 75% and 100%): (a) SnI-2D-HOIPs and (b) SnBr-2D-HOIPs.

Figure 6

(a) Formation energies of the 2D SnI-based systems with various mixed atoms (Cs, Rb, Ge, and Pb). (b) Bandgaps of the 2D SnI-based systems with various mixed atoms (Cs, Rb, Ge, and Pb). (c) Carrier effective masses for the 2D SnI-based systems with various mixed atoms (Cs, Rb, Ge, and Pb).

Figure 7

(a) Adsorption sites of water molecules. (b) Adsorption energies of water molecule for the various atoms (Cs, Rb, Ge, and Pb) mixed 2D SnI-based systems. The dashed line in (b) indicates the lowest H₂O-adsorption energy on the pure 2D SnI-based system.