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As the global demand for clean and sustainable energy continues to surge, the photovoltaic sector remains at the forefront of this transition. Lead halide perovskite solar cells (LHPs) have long been celebrated for their remarkable power conversion efficiencies (PCEs), which have rapidly progressed to over 26% for single-junction cells. However, despite their outstanding performance, the widespread commercialization of LHPs faces persistent challenges.

The inherent toxicity of lead compounds and their pronounced instability under real-world conditions, particularly when exposed to heat, moisture and light, raise concerns about environmental safety and device longevity.

To address these critical issues, my research team at the Autonomous University of Querétaro, Mexico, has turned its attention to lead-free chalcogenide perovskites. Among these promising materials, BaZrS₃ has emerged as an excellent alternative absorber due to its direct bandgap of approximately 1.7 eV, strong optical absorption and exceptional structural stability under diverse environmental conditions. Its naturally high p-type conductivity and earth-abundant elemental composition make it a sustainable and scalable solution for next-generation solar cells.

Recognizing that the hole transport layer (HTL) plays a vital role in achieving high-efficiency and long-lasting photovoltaic devices, we investigated the potential of inorganic delafossite HTLs, specifically CuFeO₂, CuGaO₂, and CuAlO₂. These materials offer advantages over traditional organic HTLs like Spiro-OMeTAD, including lower cost, greater thermal and chemical stability, and favorable energy band alignment with BaZrS₃.

Using the SCAPS-1D simulation tool, developed by Marc Burgelman at Ghent University, we performed a comprehensive theoretical study to optimize device parameters. Over multiple simulations, we fine-tuned absorber acceptor densities, controlled defect concentrations, adjusted absorber thickness, and explored the influence of interfacial defect states at both the electron transport layer (ETL) and HTL junctions.

Advanced analysis methods, such as Nyquist plots, Mott-Schottky curves, and quantum efficiency studies, were applied to gain a detailed understanding of the charge transport dynamics and recombination behavior.

Our findings, in Inorganic Chemistry Communications, demonstrate that through meticulous device engineering, BaZrS₃-based chalcogenide perovskites can achieve significant performance gains.

The results indicate that careful engineering of BaZrS₃-based devices with delafossite HTLs can yield impressive PCEs exceeding 28%, a substantial milestone for lead-free solar technology. The devices integrated with CuFeO₂ achieved a remarkable PCE of 28.35%, while CuGaO₂ and CuAlO₂ configurations attained 27.83% and 25.05%, respectively. Notably, these inorganic HTLs outperformed or matched Spiro-OMeTAD, underscoring their immense promise as robust, eco-friendly alternatives.

This pioneering work not only showcases the high potential of BaZrS₃ as a non-toxic solar absorber but also provides the first comprehensive theoretical validation of delafossite HTLs within this material system. As the renewable energy sector accelerates its shift away from hazardous materials, our findings provide vital insights for researchers and industry partners seeking to develop durable, scalable, and environmentally responsible photovoltaic devices for a sustainable energy future.

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Dr. Latha Marasamy is a Research Professor at the Faculty of Chemistry-Energy Science Program at UAQ, where she leads a dynamic team of international students and researchers. Her mission is to advance renewable energy, particularly in the development of second and third-generation solar cells, which include CdTe, CIGS, emerging chalcogenide perovskites, lead-free FASnI₃ perovskites, quaternary chalcogenides of I2-II-IV-VI4, and hybrid solar cells. She is working with a range of materials such as CdTe, CIGSe, CdS, MOFs, graphitic carbon nitride, chalcogenide perovskites (ABX3, where A = Ba, Sr, Ca; B = Zr, Hf; X = S, Se), quaternary chalcogenides (I2-II-IV-VI4, where I = Cu, Ag; II = Ba, Sr, Co, Mn, Fe, Mg; IV = Sn, Ti; VI = S, Se), antimony based Sb₂Se₃, Sb₂(S,Se₃) and CuSb(S,Se)₂, metal oxides, MXenes, ferrites, plasmonic metal nitrides, FASnI₃ and borides for these applications.