There has been an urgent need to eliminate toxic lead from the prevailing halide perovskite solar cells (PSCs), but the current lead-free PSCs are still plagued with the critical issues of low efficiency and poor stability. This is primarily due to their inadequate photovoltaic properties and chemical stability. Herein we demonstrate the use of the lead-free, all-inorganic cesium tin-germanium triiodide (CsSn0.5Ge0.5I3) solid-solution perovskite as the light absorber in PSCs, delivering promising efficiency of up to 7.11%. More importantly, these PSCs show very high stability, with less than 10% decay in efficiency after 500 h of continuous operation in N2 atmosphere under one-sun illumination. The key to this striking performance of these PSCs is the formation of a full-coverage, stable native-oxide layer, which fully encapsulates and passivates the perovskite surfaces. The native-oxide passivation approach reported here represents an alternate avenue for boosting the efficiency and stability of lead-free PSCs.
Surface plasmons that propagate along cylindrical metal/dielectric interfaces in annular apertures in metal films, called cylindrical surface plasmons (CSPs), exhibit attractive optical characteristics. However, it is challenging to fabricate these nanocoaxial structures. Here, we demonstrate a practical low-cost route to manufacture highly ordered, large-area annular cavity arrays (ACAs) that can support CSPs with great tunability. By employing a sol-gel coassembly method, reactive ion etching and metal sputtering techniques, regular, highly ordered ACAs in square-centimeter-scale with a gap width tunable in the range of several to hundreds of nanometers have been produced with good reproducibility. Ag ACAs with a gap width of 12 nm and a gap height of 635 nm are demonstrated. By finite-difference time-domain simulation, we confirm that the pronounced dips in the reflectance spectra of ACAs are attributable to CSP resonances excited in the annular gaps. By adjusting etching time and Ag film thickness, the CSP dips can be tuned to sweep the entire optical range of 360 to 1800 nm without changing sphere size, which makes them a promising candidate for forming integrated plasmonic sensing arrays. The high tunability of the CSP resonant frequencies together with strong electric field enhancement in the cavities make the ACAs promising candidates for surface plasmon sensors and SERS substrates, as, for example, they have been used in liquid refractive index (RI) sensing, demonstrating a sensitivity of 1505 nm/RIU and a figure of merit of 9. One of the CSP dips of ACAs with a certain geometry size is angle- (0-70 degrees) and polarization-independent and can be used as a narrow-band absorber. Furthermore, the nano annular cavity arrays can be used to construct solar cells, nanolasers and nanoparticle plasmonic tweezers.
We report on plasmon-enhanced hybrid organic−inorganic perovskite solar cells with methylammonium lead iodide (MAPbI 3 ) as the active absorbing material. Three-dimensional finite-difference time-domain simulations were performed on perovskite solar cells that consist of perovskite films with varied thicknesses on top of corrugated gold electrodes with different light trapping geometries, such as arrays of nanoholes and nanodisks. The absorption within the perovskite and gold films was estimated by calculating the electric field at every mesh point within the simulation volume, which allowed for the calculation of the solar cell power conversion efficiency (PCE) as a function of relevant design parameters. Optimal nanostructure designs were obtained by systematically varying the geometry dimensions. The results show that 100 nm-thick perovskite films on top of corrugated gold electrodes can exhibit up to 52% increase in PCE compared to their flat counterparts (i.e., from 19.2% for a flat cell to 29.2% for an optimized nanocorrugated cell). Moreover, we show that a 150 nm-thick perovskite film cell with opportunely corrugated back metal contacts can exhibit a PCE value of 31.3%, which is comparable to that of a 400 nm-thick bulk-like cell (31.6%). These findings may pave the way for plasmon-enhanced high-performance perovskite solar cells with ultrathin absorbing layers.
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