<p>➀ Researchers from Autonomous University of Querétaro developed solar cells using non-toxic (Ca,Ba)ZrS₃ chalcogenide perovskite and spinel oxides (NiCo₂O₄, ZnCo₂O₄, etc.) as hole transport layers (HTLs), achieving over 34% power conversion efficiency (PCE).</p><p>➁ The SrFe₂O₄ spinel HTL demonstrated optimal performance with 34.24% PCE, low energy loss (~0.11 V), and high light absorption (~42%), attributed to improved band alignment and interface engineering.</p><p>➂ This eco-friendly, lead-free approach combines stability, scalability, and superior efficiency, positioning spinel-integrated solar cells as a promising solution for next-generation renewable energy systems.</p>