Stable and Colorful Perovskite Solar Cells Using a Nonperiodic SiO2/TiO2 Multi-Nanolayer Filter

While research on building-integrated photovoltaics (BIPVs) has mainly focused on power-generating window applications, the utilization of other underutilized surface areas in buildings, including exteriors, facades, and rooftops, has still not been fully explored. The most important requirements for BIPVs are color, power conversion efficiency (PCE), and long-term stability. In this work, we achieved colorful (red, green, blue, RGB) perovskite solar cells (PSCs) with minimized PCE loss (<10%) and enhanced photostability by exploiting the optical properties of nonperiodic multi-nanolayer, narrow-bandwidth reflective filters (NBRFs). The NBRFs were fabricated by multilayering high-index TiO2/low-index SiO2 in a nonperiodic manner, which allowed devices to demonstrate various colors with effectively suppressed unwanted baseline ripple-shape reflectance. The PCEs of PSCs with nonperiodic RGB-NBRFs were 18.0%, 18.6%, and 18.9%, which represent reductions of only 10%, 7%, and 6% of PCE values, respectively, compared to a black control PSC (20.1%). Moreover, the photostability of the PSCs was substantially improved by using the NBRFs because of ultraviolet blocking in the TiO2 layers. The G-PSC retained 65% of the initial PCE after 60 h of continuous illumination (AM 1.5G one sun) at the maximum power point, whereas the black PSC retained only 30%. Aesthetic color value, low PCE loss, and enhanced photostability of PSCs were simultaneously achieved by employing our NBRFs, making this a promising strategy with potential applicability in power-generating building exteriors

Newly Developed Broadband Antireflective Nanostructures by Coating a Low-Index MgF2 Film onto a SiO2 Moth-Eye Nanopattern

A newly developed nanopatterned broadband antireflective (AR) coating was fabricated on the front side of a glass/indium tin oxide/perovskite solar cell (PSC) by depositing a single interference layer onto a two-dimensional (2D)-patterned moth-eye-like nanostructure. The optimized developed AR nanostructure was simulated in a finite-difference time domain analysis. To realize the simulated developed AR nanostructure, we controlled the SiO2 moth-eye structure with various diameters and heights and a MgF2 single layer with varying thicknesses by sequentially performing nanosphere lithography, reactive ion etching, and electron-beam evaporation. Optimization of the developed AR nanostructure, which has a 100 nm-thick MgF2 film coated onto the SiO2 moth-eye-like nanostructure (diameter 165 nm and height 400 nm), minimizes the reflection loss throughout the visible range. As a result, the short-circuit current density (JSC) of the newly AR-coated PSC increases by 11.80%, while the open-circuit voltage (VOC) remains nearly constant. Therefore, the power conversion efficiency of the newly developed AR-decorated PSC increases by 12.50%, from 18.21% for a control sample to 20.48% for the optimum AR-coated sample. These results indicate that the newly developed MgF2/SiO2 AR nanostructure can provide an advanced platform technology that reduces the Fresnel loss and therefore increases the possibility of the commercialization of glass-based PSCs

Multiple-Color-Generating Cu(In,Ga)(S,Se)₂ Thin-Film Solar Cells via Dichroic Film Incorporation for Power-Generating Window Applications

There are four prerequisites when applying all types of thin-film solar cells to power-generating window photovoltaics (PVs): high power-generation efficiency, longevity and high durability, semitransparency or partial-light transmittance, and colorful and aesthetic value. Solid-type thin-film Cu­(In,Ga)­S₂ (CIGS) or Cu­(In,Ga)­(S,Se)₂ (CIGSSe) PVs nearly meet the first two criteria, making them promising candidates for power-generating window applications if they can transmit light to some degree and generate color with good aesthetic value. In this study, the mechanical scribing process removes 10% of the window CIGSSe thin-film solar cell with vacant line patterns to provide a partial-light-transmitting CIGSSe PV module to meet the third requirement. The last concept of creating distinct colors could be met by the addition of reflectance colors of one-dimensional (1D) photonic crystal (PC) dichroic film on the black part of a partial-light-transmitting CIGSSe PV module. Beautiful violets and blues were created on the cover glass of a black CIGSSe PV module via the addition of 1D PC blue-mirror–yellow-pass dichroic film to improve the aesthetic value of the outside appearance. As a general result from the low external quantum efficiency (EQE) and absorption of CIGSSe PVs below a wavelength of 400 nm, the harvesting efficiency and short-circuit photocurrent of CIGSSe PVs were reduced by only ∼10% without reducing the open-circuit voltage (<i>V</i>_OC) because of the reduced overlap between the absorption spectrum of CIGSSe PV and the reflectance spectrum of the 1D PC blue-mirror–yellow-pass dichroic film. The combined technology of partial-vacancy-scribed CIGSSe PV modules and blue 1D PC dichroic film can provide a simple strategy to be applied to violet/blue power-generating window applications, as such a strategy can improve the transparency and aesthetic value without significantly sacrificing the harvesting efficiency of the CIGSSe PV modules