Perovskite solar cells have evolved as a revolutionary photovoltaic technology in just over a decade, with power conversion efficiencies that have been proven to be higher than 26%. The exceptional performance of these materials can be attributed to the exceptional optoelectronic properties of ABX3-structured materials. These properties include the long diffusion lengths of charge carriers and high absorption coefficients. A substantial amount of research has been conducted on non-toxic, all-inorganic alternatives as a result of concerns with the long-term stability of high-performance formulations and the toxicity of lead.
This computational study aims to employ SCAPS-1D device modelling to predict novel lead-free photovoltaic absorbers utilising copper(I) perovskite chlorides (CuMClₜ, where M = Fe, Cr, Zn) with a target power conversion efficiency (PCE) of 23%. CuMCl₃ compounds are selected due to their lower total energies compared to caesium-based alternatives and their direct, tuneable bandgaps ranging from 1.4 to 1.6 eV, which closely approach the optimal Shockley-Queisser limit for single-junction cells. These compounds exhibit enhanced projected electron and hole mobilities by diminishing their carrier effective masses in comparison to CsPbCl₃. The A-site cation not only contributes to structural stability but also, due to its distinctive hybridisation of Cu⁺ and MCl₆ orbitals, plays an active role in the electronic structure, influencing electrical characteristics.
Detailed SCAPS-1D simulations of a conventional n-i-p architecture (FTO/TiO₂/CuFeCl₃/Spiro-OMeTAD/Au) demonstrated that CuFeCl₃ had an exceptional capability characterised by a bandgap of 1.45 eV. Through the precise optimisation of layer thickness, doping density, and interface characteristics, a simulated device achieved a peak power conversion efficiency of 23.2%. The performance of the device is characterised by an open-circuit voltage (VOC) of 1.12 V, a short-circuit current density (JSC) of 26.8 mA/cm², and a fill factor of 77.4%. A key benefit is the improved volatile organic compound (VOC), which signifies a minimal voltage deficit and implies a decrease in non-radiative recombination. Notwithstanding defect densities of 10⁴ cm⁻³, the material demonstrated exceptional defect tolerance inside the absorber bulk, maintaining an efficiency above 20%. The performance exhibited significant sensitivity to the quality of the interface. To limit recombination losses, it is crucial that the defect concentrations at the interfaces of the charge transport layer remain below 10 cm⁻².
The results indicate that Cu⁺-based perovskites have considerable promise as next-generation, lead-free photovoltaic materials, accomplished by optimising the all-inorganic composition for improved optoelectronic properties. The research offers a definitive theoretical framework and performance standards for experimental synthesis. Nevertheless, considerable obstacles remain, including the experimental stability of Cu⁺ inside the perovskite lattice to prevent oxidation and the reduction of moderate near-infrared absorption, which requires rather thick active layers. Addressing these issues via sophisticated manufacturing and interface engineering will be essential for converting this promising theoretical prediction into a high-performance, stable, and environmentally friendly solar cell technology.
