Photovoltaic & Optoelectronic Device Group

Abstract:

Molecular piezoelectrics are a potentially disruptive technology, enabling a new generation of self-powered electronics that are flexible, high performing, and inherently low in toxicity. Although significant efforts have been made toward understanding their structural design by targeted manipulation of phase transition behavior, the resulting achievable piezoresponse has remained limited. In this work, we use a low-symmetry, zero-dimensional (0D) inorganic framework alongside a carefully selected ‘quasi-spherical’ organic cation to manipulate organic–inorganic interactions and thus form the hybrid, piezoelectric material [(CH3)3NCH2I]3Bi2I9. Using variable–temperature single crystal X-ray diffraction and solid-state nuclear magnetic resonance spectroscopy, we demonstrate that this material simultaneously exhibits an order–disorder and displacive symmetry-breaking phase transition. This phase transition is mediated by halogen bonding between the organic and inorganic frameworks and results in a large piezoelectric response, d 33 = 161.5 pm/V. This value represents a 4-fold improvement on previously reported halobismuthate piezoelectrics and is comparable to those of commercial inorganic piezoelectrics, thus offering a new pathway toward low-cost, low-toxicity mechanical energy harvesting and actuating devices.

Abstract:

Perovskite solar cells represent a promising technology in the photovoltaic industry due to their high power conversion efficiency, potential for cost-effective manufacturing and versatile applications. The most stable and efficient perovskites to date rely on lead (Pb), raising concerns about leaching into the environment; however Pb release so far has only been quantified under laboratory conditions, and no field-based assessment under real outdoor expsosure has yet evaluated this risk. The present study quantified Pb leaching from various metal-halide perovskite compositions, device stacks and encapsulation approaches in a rooftop installation for up to 9 months. Pb leaching was low across all tested configurations, even in intentionally damaged materials. Glass–glass encapsulated tandem devices shattered by hail and plastic-encapsulated samples damaged by 100 µm pinholes released only 0.07% ± 0.01% and 0.15% ± 0.14% of their initial Pb, respectively, likely due to the slow diffusion of Pb cations in water. The highest leaching (4.81% ± 0.02%) occurred in unlaminated laboratory devices, demonstrating the importance of proper lamination. A self-developed freeware web tool was used to calculate predicted soil concentrations and evaluate potential impacts. Even for unlaminated devices, concentrations would only slightly exceed natural background levels (5.6 mg kg−1 increase), with negligible effects on soil fertility. A hypothetical worst-case scenario assuming a 1000 nm thick perovskite layer and complete Pb leaching onto a narrow strip of soil predicted a negative impact on soil fertility; however remediation would still not be required under Swiss environmental regulations. Overall, current industry-standard encapsulation limits Pb leaching to levels that almost completely mitigate negative impacts on soil health.

Abstract:

All-inorganic halide perovskite materials have attracted significant interest for display applications because of their narrow bandwidths and high photoluminescence quantum yields. However, the development of blue-light-emitting perovskite materials has been slower than that of green- and red-light-emitting perovskites. In this study, we successfully produced single-halide CsPbBr3 nanoplatelets with a quantum confinement effect using ligand-assisted reprecipitation techniques. NaBr, an inorganic ligand with strong binding affinity (adsorption energy, -2.13 eV) and low steric hindrance, was used to prevent the continued growth of nanoplatelets. A series of experimental results demonstrate that CsPbBr3 nanoplatelets with a dense Na+ shell on the surface exhibit stable deep blue emission. UV chip-based light-emitting devices activated by these nanoplatelets demonstrated remarkable spectral stability as the current injection increased. Moreover, the synthesis process is conducted under simple conditions at room temperature, demonstrating potential for batch production.

Abstract:

<jats:p>This study pioneers a solvent-additive cascade strategy to achieve crystallographically homogenous perovskite films, breaking the efficiency–stability trade-off by harnessing facet-dependent properties for record performance.</jats:p>