Broadband light absorbers are highly desirable in various applications including solar-energy harvesting, thermo-photovoltaics, and photon detection. The Fabry−Perot (F−P) cavity comprising metal−insulator−metal (MIM) layers has attracted enormous interest as a lithography-free structure for realizing planar super absorbers. However, typical F−P cavity exhibits a narrow absorption band, and efforts have thus been made to increase the absorption bandwidth. This study demonstrates that near-perfect absorption over a broad spectral range can be obtained from the MIM structure by using thermally evaporated Ag and Au thin films whose dielectric and optical properties are much different from bulk-state properties because of their nanoscale features. A 55 nm thick SiO 2 spacer sandwiched between a 10 nm Ag top layer and a 100 nm Al back reflector exhibits absorption >95% in the visible range of 400−700 nm. The broad absorption band shifts to a near-infrared range of 650−1000 nm by replacing the top layer with a 10 nm thick Au film and increasing the SiO 2 spacer thickness to 115 nm. The experimental results are supported by finite-difference time-domain simulation. The large absorption bandwidth is attributed to the lossy nature of the nanostructured top metallic layer combined with the resonant absorption of the MIM cavity.

No abstract

Perovskite solar cells (PSCs) fabricated on transparent polymer substrates are considered a promising candidate as flexible solar cells that can emulate the advantages of organic solar cells, which exhibit considerable freedom in their device design thanks to their light weight and mechanically flexibility while achieving high photocurrent conversion efficiency, comparable to that of their conventional counterparts fabricated on rigid glasses. However, the full realization of highly efficient, flexible PSCs is largely prevented by technical difficulties in simultaneously attaining a transparent electrode with efficient charge transport to meet the specifications of PSCs. In this study, an effective strategy for resolving this technical issue has been devised by proposing a simple but highly effective technique to fabricate an efficient, multilayer TiO 2 /Ag (O) /ZnO (TAOZ) configuration. This configuration displays low losses in optical transmittance and electrical conductivity owing to its completely continuous, ultrathin metallic Ag (O) transparent electrode, and any notable current leakage is suppressed by its pinhole-free TiO 2 electron transport layer. These features are a direct consequence of the rapid evolution of Ag (O) and TiO 2 into ultrathin, completely continuous, pinhole-free layers owing to the dramatically improved wetting of metallic Ag (O) with a minimal dose of oxygen (ca. 3 at%) during sputtering. The TAOZ configuration exhibits an average transmittance of 88.5% in the spectral range of 400-800 nm and a sheet resistance of 8.4 U sq À1 while demonstrating superior mechanical flexibility to that of the conventional TiO 2 on ITO configuration. The photocurrent conversion efficiency of flexible PSCs is significantly improved by up to 11.2% thanks to an optimum combination of optoelectrical performance and pinhole-free morphologies in the TAOZ configuration. † Electronic supplementary information (ESI) available: XPS and XRD analyses of Ag and Ag (O) TEs, FE-SEM images of different OMOs, 2D and 3D AFM images of OMOs, reectance, absorbance and transmittance of OMOs. SeeFig. 2 Morphological comparison of Ag and Ag (O) deposited on two different bottom oxide layers: TiO 2 and ZnO. The FE-SEM images showed the highly magnified planar surfaces of Ag and Ag (O) in different configurations: (a) Ag on TiO 2 (Ag/TiO 2 ), (b) Ag on ZnO (Ag/ZnO), (c) Ag (O) on TiO 2 (Ag (O) /TiO 2 ), and (d) Ag (O) on ZnO (Ag (O) /ZnO). Images of the morphologies of Ag and Ag (O) were captured at different nominal thicknesses: 3.0, 6.0 and 7.5 nm, from top to bottom. This journal isView Article Online a J sc , short-circuit current density; V oc , open-circuit voltage; FF, ll factor; R s , series resistance; R sh , shunt resistance; PCE, photocurrent conversion efficiency. Each parameter was averaged for 6 cells, fabricated using each OMO type. Data are presented as the average plus or minus the standard deviation.This journal is

No abstract