Abstract
In recent years, lead-free metal-halide perovskite photovoltaics has attracted ever-growing attention, in view of its potential to replicate the outstanding properties of lead-halide perovskite photovoltaics, but without the toxicity burden of the latter. Despite a research effort much smaller in scale than that pursued with lead-based perovskites, considerable progress has been achieved in lead-free perovskite photovoltaics, with the highest power conversion efficiencies now being in the region of 13%. In this Perspective, we first discuss the state of the art of lead-free perovskite photovoltaics and additionally highlight promising directions and strategies that could lead to further progress in material exploration and understanding as well as in photovoltaic efficiency. Furthermore, we point out the widespread lack of experimental data on the fundamental optoelectronic properties of lead-free halide perovskite absorbers (e.g., charge carrier mobility, defect parameters, Urbach energy, and the impact of dimensionality). All of this currently hampers a rational approach to further improving their performance and points to the need for a concerted effort that could bridge this knowledge gap. Additionally, this Perspective brings to the fore the manifold photovoltaic opportunities—thus far largely unexplored with lead-free perovskite absorbers—beyond single-junction outdoor photovoltaics, which may potentially enable the realization of their full potential. The exploration of these opportunities (tandem photovoltaics, indoor photovoltaics, and building-integrated and transparent photovoltaics) could energize the investigation of existing and new classes of lead-free perovskite absorbers beyond current paradigms and toward high photovoltaic performance.
Highlights
Over the past decade, lead-halide perovskites have reached prominence in photovoltaics and beyond,1–6 delivering a tremendous rise in single-junction power conversion efficiency (PCE)7 through remarkably simple manufacturing processes
Despite a research effort much smaller in scale than that pursued with lead-based perovskites, considerable progress has been achieved in lead-free perovskite photovoltaics, with the highest power conversion efficiencies being in the region of 13%
This Perspective provides a timely fresh look at the status and prospects of the rapidly evolving area of lead-free perovskite absorbers for photovoltaics. It first surveys the main classes of lead-free metal-halide perovskite absorbers—tin-based, germanium-based, bismuth-based, and antimony-based and halide double perovskites (HDPs)—highlighting the most promising solutions explored to date
Summary
Lead-halide perovskites have reached prominence in photovoltaics and beyond, delivering a tremendous rise in single-junction power conversion efficiency (PCE) ( greater than 25%) through remarkably simple manufacturing processes. Considerable progress has been recently achieved in this area—with their highest single-junction PCE at 13.2%—despite a research effort incomparably smaller in scale and spanning a much shorter time than lead-based perovskite photovoltaics research This Perspective provides a timely fresh look at the status and prospects of the rapidly evolving area of lead-free perovskite absorbers for photovoltaics. General strategies that may enable these challenges to be overcome are jointly discussed This Perspective highlights key outstanding questions in the area of lead-free perovskite absorbers for photovoltaics, identifying as a priority area the detailed investigation of their charge transport and defect properties, as well as the role of dimensionality. This Perspective looks at the opportunities beyond single-junction solar harvesting that could realize the full photovoltaic potential of lead-free perovskites in the near future
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