Publications by authors named "Yanfa Yan"

Cumulative silicon photovoltaic (PV) waste highlights the importance of considering waste recycling before the commercialization of emerging PV technologies. Perovskite PVs are a promising next-generation technology, in which recycling their end-of-life waste can reduce the toxic waste and retain resources. Here we report a low-cost, green-solvent-based holistic recycling strategy to restore all valuable components from perovskite PV waste.

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Wide band gap FACsPb(IBr) perovskite photovoltaic (PV) devices are measured by spectroscopic ellipsometry in the through-the-glass configuration and analyzed to determine the complex optical property spectra of the perovskite absorber as well as the structural properties of all constituent layers. This information is used to simulate external quantum efficiency (EQE) spectra, to calculate PV device performance parameters such as short circuit current density, open circuit voltage, fill factor, and power conversion efficiency, and to develop strategies for increasing the accuracy of predictions. Simulations and calculations tend to overestimate PV device performance parameters, undermining the accuracy and usefulness of those simulations.

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Article Synopsis
  • Engineering a perovskite precursor ink is essential for creating high-quality, uniform films suitable for large-scale manufacturing using solution coating methods.
  • A ternary solvent system, using NMP and DMPU, is explored to improve the physical properties of slot-die-coated perovskite films and enhance device performance.
  • By optimizing the concentrations of these solvents, researchers achieve a wider processing window and successfully produce perovskite minimodules with significant power conversion efficiencies of 19% and 16% on different substrate sizes.*
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The light-emitting diodes (LEDs) used in indoor testing of perovskite solar cells do not expose them to the levels of ultraviolet (UV) radiation that they would receive in actual outdoor use. We report degradation mechanisms of p-i-n-structured perovskite solar cells under unfiltered sunlight and with LEDs. Weak chemical bonding between perovskites and polymer hole-transporting materials (HTMs) and transparent conducting oxides (TCOs) dominate the accelerated A-site cation migration, rather than direct degradation of HTMs.

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Article Synopsis
  • * While interfacial materials like fullerenes can capture iodide ions, they actually worsen the problem by creating more iodine vacancies.
  • * In contrast, perfluorodecyl iodide effectively captures and confines iodide ions, resulting in inverted perovskite solar cells that show significant improvements in stability against ultraviolet light and heat.
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Circularly polarized light emission is a crucial application in imaging, sensing, and photonics. However, utilizing low-energy photons to excite materials, as opposed to high-energy light excitation, can facilitate deep-tissue imaging and sensing applications. The challenge lies in finding materials capable of directly generating circularly polarized nonlinear optical effects.

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Surface defects in semiconducting materials, though they have been widely studied, remain a prominent source of loss in optoelectronic devices; here we sought a new angle of approach, looking into the dynamic roles played by surface defects under atmospheric stressors and their chemical passivants in the lifetime of optoelectronic materials. We find that surface defects possess properties distinct from those of bulk defects. ab initio molecular dynamics simulations reveal a previously overlooked reversible degradation mechanism mediated by hydrogen vacancies.

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Frequency domain characterization has long served as an important method for the examination of diverse kinetic processes that occur in solar cells. In this study, we investigated the dynamic response of high-efficiency perovskite solar cells utilizing ultra-low-intensity-modulated photocurrent spectroscopy. Distinctive intensity-modulated photocurrent spectroscopy (IMPS) attributes were detected only as a result of this low-intensity modulation, and their evolution under light and voltage bias was investigated in detail.

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Tin (Sn)-containing perovskite solar cells (PSCs) have gained significant attention in the field of perovskite optoelectronics due to lower toxicity than their lead-based counterparts and their potential for tandem applications. However, the lack of stability is a major concern that hampers their development. To achieve the long-term stability of Sn-containing PSCs, it is crucial to have a clear and comprehensive understanding of the degradation mechanisms of Sn-containing perovskites and develop mitigation strategies.

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The spin-orbit coupling (SOC) effect of lead (Pb) atoms is a consequential attribute of the unique optoelectronic and defect properties of lead halide perovskites (LHPs). It has been found that the SOC effect varies significantly as the structural dimensionality changes with an anomalous dependence; i.e.

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Metal halide perovskite solar cells (PSCs) represent a promising low-cost thin-film photovoltaic technology, with unprecedented power conversion efficiencies obtained for both single-junction and tandem applications. To push PSCs towards commercialization, it is critical, albeit challenging, to understand device reliability under real-world outdoor conditions where multiple stress factors (for example, light, heat and humidity) coexist, generating complicated degradation behaviours. To quickly guide PSC development, it is necessary to identify accelerated indoor testing protocols that can correlate specific stressors with observed degradation modes in fielded devices.

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Achromatic quarter waveplates (A-QWPs), traditionally constructed from multiple birefringent crystals, can modulate light polarization and retardation across a broad range of wavelengths. This mechanism is inherently related to phase retardation controlled by the fast and slow axis of stacked multi-birefringent crystals. However, the conventional design of A-QWPs requires the incorporation of multiple birefringent crystals, which complicates the manufacturing process and raises costs.

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The defective bottom interfaces of perovskites and hole-transport layers (HTLs) limit the performance of p-i-n structure perovskite solar cells. We report that the addition of lead chelation molecules into HTLs can strongly interact with lead(II) ion (Pb), resulting in a reduced amorphous region in perovskites near HTLs and a passivated perovskite bottom surface. The minimodule with an aperture area of 26.

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Light-induced performance changes in metal halide perovskite solar cells (PSCs) have been studied intensively over the last decade, but little is known about the variation in microscopic optoelectronic properties of the perovskite heterojunctions in a completed device during operation. Here, we combine Kelvin probe force microscopy and transient reflection spectroscopy techniques to spatially resolve the evolution of junction properties during the operation of metal-halide PSCs and study the light-soaking effect. Our analysis showed a rise of an electric field at the hole-transport layer side, convoluted with a more reduced interfacial recombination rate at the electron-transport layer side in the PSCs with an n-i-p structure.

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The structural and optical properties of hybrid organic-inorganic metal halide perovskite solar cells are measured by spectroscopic ellipsometry to reveal an optically distinct interfacial layer among the back contact metal, charge transport, and absorber layers. Understanding how this interfacial layer impacts performance is essential for developing higher performing solar cells. This interfacial layer is modeled by Bruggeman effective medium approximations (EMAs) to contain perovskite, C, BCP, and metal.

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The tunable bandgaps and facile fabrication of perovskites make them attractive for multi-junction photovoltaics. However, light-induced phase segregation limits their efficiency and stability: this occurs in wide-bandgap (>1.65 electron volts) iodide/bromide mixed perovskite absorbers, and becomes even more acute in the top cells of triple-junction solar photovoltaics that require a fully 2.

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Lewis base molecules that bind undercoordinated lead atoms at interfaces and grain boundaries (GBs) are known to enhance the durability of metal halide perovskite solar cells (PSCs). Using density functional theory calculations, we found that phosphine-containing molecules have the strongest binding energy among members of a library of Lewis base molecules studied herein. Experimentally, we found that the best inverted PSC treated with 1,3-bis(diphenylphosphino)propane (DPPP), a diphosphine Lewis base that passivates, binds, and bridges interfaces and GBs, retained a power conversion efficiency (PCE) slightly higher than its initial PCE of ~23% after continuous operation under simulated AM1.

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Article Synopsis
  • The development of stable and efficient wide-bandgap perovskite solar cells using bromine-iodine mixed halides (with over 20% Br) is essential for creating tandem solar cells.
  • Issues like phase segregation under light and heat limit the performance of these solar cells, primarily due to defects from the rapid crystallization of Br-rich perovskites.
  • By combining rapid crystallization with a gentle gas-quench method, researchers produced high-quality 1.75-eV Br-I mixed WBG perovskite films that achieved over 20% efficiency, along with promising stability and integration into a tandem device with a total efficiency of 27.1%.
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Bandgap gradient is a proven approach for improving the open-circuit voltages (Vs) in Cu(In,Ga)Se and Cu(Zn,Sn)Se thin-film solar cells, but has not been realized in Cd(Se,Te) thin-film solar cells, a leading thin-film solar cell technology in the photovoltaic market. Here, we demonstrate the realization of a bandgap gradient in Cd(Se,Te) thin-film solar cells by introducing a Cd(O,S,Se,Te) region with the same crystal structure of the absorber near the front junction. The formation of such a region is enabled by incorporating oxygenated CdS and CdSe layers.

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Introducing chirality into the metal-halide hybrids has enabled many emerging properties including chiroptical activity, spin-dependent transport, and ferroelectricity. However, most of the chiral metal-halide hybrids to date are non-emissive, and the underlying mechanism remains elusive. Here, we show a new strategy to turn on the circularly polarized luminescence (CPL) in chiral metal-halide hybrids.

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The open-circuit voltage (V) deficit in perovskite solar cells is greater in wide-bandgap (over 1.7 eV) cells than in perovskites of roughly 1.5 eV (refs.

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Perovskite solar cells (PSCs) with an inverted structure (often referred to as the p-i-n architecture) are attractive for future commercialization owing to their easily scalable fabrication, reliable operation and compatibility with a wide range of perovskite-based tandem device architectures. However, the power conversion efficiency (PCE) of p-i-n PSCs falls behind that of n-i-p (or normal) structure counterparts. This large performance gap could undermine efforts to adopt p-i-n architectures, despite their other advantages.

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The performance of CdTe solar cells has advanced impressively in recent years with the incorporation of Se. Instabilities associated with light soaking and copper reorganization have been extensively examined for the previous generation of CdS/CdTe solar cells, but instabilities in Cu-doped Se-alloyed CdTe devices remain relatively unexplored. In this work, we fabricated a range of CdSe/CdTe solar cells by sputtering CdSe layers with thicknesses of 100, 120, 150, 180, and 200 nm on transparent oxide-coated glass and then depositing CdTe by close-spaced sublimation.

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Article Synopsis
  • * Introducing a low concentration of barium ions (0.1 mol%) effectively compensates for p-doping, creating a p-n homojunction without altering the bandgap.
  • * This innovative gradient doping technique improves carrier extraction and boosts the efficiencies of Sn-Pb perovskite solar cells significantly, achieving over 21% for single-junction cells and 25.3% for tandem configurations.
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