Lead-free

Researchers from Xi’an University of Architecture and Technology, Xidian University, Xi’an Jiaotong University, University of New South Wales, Beijing University of Posts and Telecommunications and Ningbo Weiyuan Optoelectronic Research Institute have developed a machine learning-assisted screening strategy to identify lead-free double perovskite materials tailored for agrivoltaic applications, where photovoltaic performance must be balanced with crop light requirements.

Agrivoltaic systems place unique constraints on solar absorbers: in addition to high power conversion efficiency, materials must allow selective transmission of photosynthetically useful light. While silicon solar cells can reach efficiencies of 29.4%, their opacity limits plant growth. Semitransparent technologies such as perovskite solar cells (PSCs), with certified efficiencies up to 27.3%, offer a more suitable platform due to their tunable absorption spectra. However, conventional lead-based PSCs face stability and toxicity concerns, motivating the search for lead-free alternatives.

Researchers from POSTECH, SKKU and UESTC have developed air‑stable tin‑based perovskite p‑type transistors using volatile surface reconstruction by treating CsSnI₃ with potassium acetate, removing defect‑forming tin ions and creating a protective KI layer. The devices show top‑level hole mobility and on/off ratio, remain stable in air and at high temperature, and may be used in future memory and display electronics.

Tin (Sn²⁺) halide perovskites are promising lead‑free materials for future electronics because their bandgaps can be tuned and they conduct charge efficiently, but the tin at the surface is easily oxidized in air. Undercoordinated Sn²⁺ sites tend to oxidize to Sn⁴⁺, causing unwanted self‑doping and defects that block charge flow, so conventional tin‑based perovskite transistors can fail within minutes under ambient conditions. In these devices, unreacted tin ions that never fully joined the crystal remain on the surface and act as starting points for oxidation and degradation. To overcome this, the researchers implemented “volatile surface reconstruction”. 

Researchers from the University of Tokyo, RIKEN Center for Emergent Matter Science and Tohoku University have demonstrated a gigantic bulk photovoltaic response in high-quality epitaxial thin films of the lead-free ferroelectric halide perovskite CsGeI₃.

Ferroelectric halide perovskites are attractive because they combine a built‑in electric polarization with strong visible‑light absorption. In such materials, light can generate current through the bulk photovoltaic effect, which does not require a conventional p–n junction. A key part of this effect is the “shift current”, a special kind of photocurrent that comes directly from the quantum‑mechanical motion of electrons when they absorb light. In this work, the team grew high‑quality epitaxial CsGeI₃ thin films using molecular beam epitaxy. The films show clear ferroelectric behavior and allowed the researchers to probe the intrinsic bulk photovoltaic response with minimal influence from defects. Under visible‑light illumination, they found that CsGeI₃ produces an exceptionally large shift current.

Researchers from China's Jiangsu University, Zhejiang Institute of Quality Sciences and Tianjin University have developed an additive-engineering strategy combined with polymer encapsulation to significantly improve the performance and stability of lead-free CsSnI₃ perovskite photodetectors.

Tin-based perovskites such as CsSnI₃ are considered strong candidates to replace lead-based materials due to their lower toxicity, cost advantages, and favorable optoelectronic properties, including tunable bandgaps, high absorption coefficients, and strong carrier mobility. These features make them particularly suitable for photodetection across the visible to near-infrared range. However, their practical deployment has been hindered by poor stability and performance degradation, primarily driven by the oxidation of Sn²⁺ to Sn⁴⁺.

University of Perugia researchers have developed a colored passive daytime radiative cooling (PDRC) approach based on lead-free perovskite nanocrystals, addressing one of the key limitations of conventional radiative coolers: their typically white or mirror-like appearance.

PDRC systems rely on a dual optical function - high solar reflectivity and strong thermal emission in the mid-infrared (MIR) - to passively dissipate heat to the cold outer space sink (approximately 3-4 K) through atmospheric transparency windows. In practice, this requires minimizing solar absorption (typically in the 
0.25-2.5μm range) while maximizing emissivity in the 3-5μm and 8-13μm bands. However, achieving visible coloration generally introduces additional solar absorption, which increases heat gain and degrades cooling performance.

Researchers from North Carolina State University and Brown University have developed a microfluidic self-driving laboratory, termed PoLARIS (perovskite laboratory for autonomous reaction inference and synthesis), capable of rapidly optimizing and analyzing the synthesis of complex, multi-element perovskite nanocrystals. The platform addresses a key challenge in materials discovery: efficiently navigating the vast, high-dimensional parameter space associated with compositionally complex systems.

Self-driving laboratories combine automated experimentation with machine-learning-guided decision-making, but their application to materials with multiple coupled reaction pathways has remained limited. In this work, the researchers demonstrate that PoLARIS can autonomously synthesize and optimize metal halide double perovskite nanoplatelets containing up to six distinct elements, using a continuous-flow heat-up reaction.

Researchers at the University of Queensland and Southwest University have developed a vapor-based fabrication strategy for lead-free tin-based halide perovskite (THP) indoor solar cells, addressing challenges in crystallization control while achieving high efficiency under low-light conditions.

A central challenge in thermally evaporated THP films is their complex and poorly controlled crystallization kinetics, which often leads to defects and performance losses. To overcome this, the team introduced formamidine acetate (FAAc) as a vapor-deposited additive during the formation of FASnI₂Br films. FAAc coordinates with SnI₂ to form a metastable SnI₂-FAAc intermediate phase. This intermediate slows and regulates the solid-state reaction pathway, allowing more controlled crystal growth. At the same time, FAAc reduces the surface free energy of the underlying SnI₂ layer, enabling more uniform deposition of the subsequent FABr layer. This dual effect - kinetic regulation and improved film wetting - results in higher-quality perovskite films with fewer defects and significantly suppressed trap-assisted recombination.

Researchers from Zhejiang University, Shanghai University of Electric Power, Zhejiang Zheneng Wenzhou Power Generation Co., and Ningbo University of Technology have reported significant progress in tin-based, hole-transport-layer-free (HTL-free) perovskite solar cells (PSCs). Their study introduces a gradient doping strategy to enhance the optoelectronic properties of MASnI₃ absorbers through precise band engineering, achieving remarkable efficiency improvements verified by SCAPS-1D numerical simulations.

Tin-based PSCs have emerged as promising candidates for eco-friendly and lead-free photovoltaics due to tin’s non-toxic nature and favorable semiconductor characteristics, including high carrier mobility and optimal bandgaps. Yet, eliminating the traditional HTL has historically reduced device performance. The team’s approach directly tackles this limitation by creating a controlled doping gradient within the absorber, generating an internal electric field that boosts charge separation and transport efficiency.

Researchers from India's University of Calcutta have developed a flexible, lead-free perovskite solar cell that combines recycled indium tin oxide, a PET substrate, and a barium-doped Cs₂SnCl₆ absorber to deliver a power conversion efficiency of 4.95%, up from 0.79% for the undoped material. The study also shows that the device retains stability over 30 days and remains mechanically robust after 100 bending cycles, pointing to a credible route toward wearable, low-toxicity photovoltaics.

The team emphasized the use of indium tin oxide reclaimed from electronic waste, rather than freshly manufactured ITO. That transparent electrode is deposited on a PET plastic substrate, which keeps the device lightweight and flexible while also lowering the environmental footprint of the stack. The absorber is a lead-free double-perovskite composition, Cs₂(Ba_xSn_1-x)Cl₆ with x=0.1, so 10% of the Sn site is replaced by Ba.

Researchers from Tokyo's Institute of Science and Idemitsu Kosan recently reported a single‑particle photophysics study of colloidal BaZrS₃ chalcogenide perovskite quantum dots (QDs), targeting them as a lead‑free, stable alternative to halide perovskites for light‑emitting applications. BaZrS₃ offers a direct, visible‑range bandgap and robust chemical stability, and the key question here was how quantum confinement and surface defects govern its emission at the single‑QD level.

Structural and optical characterization. (a) Photo of BaZrS₃ QD toluene suspension; (b) powder XRD data of BaZrS₃ QDs (red) and BaZrS₃ reference (blue); (c) TEM image of the synthesized BaZrS₃ QDs; (d) size dispersion analyzed from the TEM images for 109 QDs; (e) high-resolution TEM image of a single QD showing the lattice fringes and d -spacing; (f ) absorption (blue) and PL (orange) spectra (normalized) of the BaZrS₃ QD toluene suspension; (g – i) high-resolution XPS spectra for the Ba 3d (g), Zr 3d (h), and S 2p (i) core levels, fitted as described in the text. Image from: Nanoscale

The team synthesized colloidal BaZrS₃ QDs by a hot‑injection method and obtained particles in the BaZrS₃ crystal phase with a broad size distribution from 2 nm to 18 nm (average 7.6 nm). This broad size range spans strong to weak quantum‑confinement regimes and is reflected in ensemble optics: weak PL (solution PLQY ≈ 5%) with peaks at 491 nm and 504 nm plus a red shoulder, consistent with a mixture of sizes and local environments. Composition analysis showed nearly ideal Ba:Zr ≈ 1:1 but significant sulfur deficiency, pointing to abundant surface traps that can quench emission and currently limit device‑ready performance.