Lead-Free MA₂CuCl_xBr_4–x Hybrid Perovskites

Abstract

Despite their extremely good performance in solar cells with efficiencies approaching 20% and the emerging application for light-emitting devices, organic-inorganic lead halide perovskites suffer from high content of toxic, polluting, and bioaccumulative Pb, which may eventually hamper their commercialization. Here, we present the synthesis of two-dimensional (2D) Cu-based hybrid perovskites and study their optoelectronic properties to investigate their potential application in solar cells and light-emitting devices, providing a new environmental-friendly alternative to Pb. The series (CH3NH3)2CuCl(x)Br(4-x) was studied in detail, with the role of Cl found to be essential for stabilization. By exploiting the additional Cu d-d transitions and appropriately tuning the Br/Cl ratio, which affects ligand-to-metal charge transfer transitions, the optical absorption in this series of compounds can be extended to the near-infrared for optimal spectral overlap with the solar irradiance. In situ formation of Cu(+) ions was found to be responsible for the green photoluminescence of this material set. Processing conditions for integrating Cu-based perovskites into photovoltaic device architectures, as well as the factors currently limiting photovoltaic performance, are discussed: among them, we identified the combination of low absorption coefficient and heavy mass of the holes as main limitations for the solar cell efficiency. To the best of our knowledge, this is the first demonstration of the potential of 2D copper perovskite as light harvesters and lays the foundation for further development of perovskite based on transition metals as alternative lead-free materials. Appropriate molecular design will be necessary to improve the material's properties and solar cell performance filling the gap with the state-of-the-art Pb-based perovskite devices.

Two-dimensional organic-inorganic hybrid perovskite: from material properties to device applications

“…Thus, the preparation methods of 3D perovskite films are supposed to be introduced in 2D perovskite films after fine-tuning. The majority of 2D perovskite films reported by now are prepared by one-step spin-coating methods [14,40,49,79,80], to be specific, depositing precursor solutions (organics and metal halides dissolved in solvents, e.g., DMF or DMSO/GBL(1/1)) on substrates. By adjusting the ratio of the precursors, the dimension of perovskite is changed.…”

Lead‐Free Hybrid Perovskite Absorbers for Viable Application: Can We Eat the Cake and Have It too?

“…Both devices exhibited good air stability with less than 5% decrease of the efficiencies after 1 d in the air with humidity of 50% without encapsulation. Later, Cortecchia et al39 reported Cl‐doped MA 2 CuBr 4 perovskites, and found that the Cl was essential for stabilizing MA 2 CuCl x Br 4− x perovskites against copper reduction and enhancing the perovskite crystallization. By tuning the Br/Cl ratio, the optical absorption can be adjusted and extended to the near‐infrared.…”

“…The XRD patterns of the C 6 H 4 NH 2 CuBr 2 I thin film showed almost no change after 4 h of immersion in water, and the printable mesoscopic solar cell based on carbon back‐contact achieved the best PCE of 0.46% (Figure 22c). The low device performance is due to low absorption coefficient (<10 5 cm −1 ),39 anisotropic charge transport in low‐dimensional structure and heavy mass of the holes. Moreover, the existence of Cu 2+ reduction could introduce higher trap density, which is unfavorable to photovoltaic performance.…”

“…Copyright 2017, RSC; Adapted with permission 38. Copyright 2016, ACS; Cu: Adapted with permission 39. Copyright 2016, ACS; Ge: Adapted with permission 40.…”

Fabrication and characterization of perovskite solar cells added with MnCl2, YCl3 or poly(methyl methacrylate)

“…In addition to their efficient light absorption and high carrier mobility, they are semiconductors with adjustable band gaps, which have the benefits to absorb different wavelengths of light and to fit into the solar devices well [1][2][3][4][5][6][7][8][9]. Further control over the optical and magnetic properties of quantum dots can be achieved through doping of transition metal ions such as Mn 2+ or Co 2+ [10].…”