The field of solar energy has made a significant leap forward thanks to the introduction of lead halide perovskite solar cells (LHPSCs). These innovative cells have achieved impressive energy conversion rates, reaching 25% in single-junction setups and 29% in tandem arrangements. However, the journey is not without hurdles; issues such as questionable long-term durability, degradation from light, heat, moisture, and the environmental risks associated with lead continue to challenge large-scale adoption and safety.

To tackle these challenges, my team at the Autonomous University of Querétaro in Mexico has explored chalcogenide perovskites, particularly a material called SrHfSe₃. This substance stands out for its exceptional chemical durability, adjustable bandgap, high ability to absorb light, and improved movement of positive charge carriers, making it a strong candidate for the next wave of solar technology.

We examined devices made with SrHfSe₃ arranged in a specific structure: FTO/BaSnO₃/SrHfSe₃/HTL/Au, initially utilizing MoS₂ as the hole transport layer (HTL). Afterward, we experimented by replacing MoS₂ with 40 different types of HTLs, which included inorganic materials, polymers, and MXenes—this comprehensive approach was a first for our research group.

Using the SCAPS-1D simulation tool from Mark Burgelman at the University of Ghent, we conducted a theoretical study that simulated 1,627 device configurations. This extensive analysis allowed us to refine key factors like the density of acceptors in the absorber, defect density, thickness, and the work functions of back contacts under very realistic conditions.

The results of our study, published in Solar Energy Materials and Solar Cells, show that with careful design, chalcogenide perovskites like SrHfSe₃ can significantly enhance performance. This research points to a bright future for efficient, stable, and lead-free solar technologies. We found improvements in light absorption, reduced energy losses during charge recombination, better charge transport, and improved built-in potential—all contributing to higher energy conversion rates.

In our analysis of the 41 different HTLs based on the 1,627 solar cell configurations, we categorized them into three main groups. We assessed the performance of the best HTLs within these categories using various techniques, including capacitance-voltage (C-V) analysis, Mott-Schottky testing, impedance spectroscopy, and quantum efficiency examinations.

Notably, the performance boost can be traced back to increased short-circuit current densities (J_SC), better splitting of quasi-Fermi levels, improved charge generation, and stronger internal electric fields. Among our simulated configurations, the top-performing setups incorporated SnS, CPE-K, and Ti₂CO₂ as HTMs, achieving power conversion efficiencies of 27.87%, 27.39%, and 26.30%, respectively.

This research marks a significant advancement in the quest for safer, high-performance alternatives to traditional perovskites. By working with SrHfSe₃ and a variety of HTLs, we have established a solid basis for creating stable, efficient, and non-toxic solar cells. As the world turns toward cleaner energy options, innovations like these could reshape the landscape of solar technology.

This article is part of Science X Dialog, which invites researchers to share findings from their published studies. To learn more about Science X Dialog and how to get involved, click here.