A recent study published in Small proposed a method to improve the UV stability of perovskite solar cells (PSCs) without compromising efficiency or flexibility. Researchers used a UV-absorbing colorless polyimide (CPI) substrate as a flexible protective layer and integrated a nanostructured transparent luminescent sticker (TLS) to minimize photocurrent loss.
Image Credit: Oleksandr Panasovskyi/Shutterstock.com
Challenges in PSC Stability
While PSCs offer high efficiency and lightweight flexibility, their long-term stability remains a challenge, particularly under UV exposure. UV light accelerates degradation by promoting thermal and moisture-induced phase decomposition. Inorganic materials and solid encapsulation techniques have been used to improve stability, but they do not fully mitigate UV-related performance loss.
Downshifting materials, which convert high-energy UV photons into lower-energy visible light, offer a promising solution. However, conventional downshifting systems have incomplete UV cut-off properties and suffer from photon loss due to isotropic emission.
This study introduces a fully UV-resistant, flexible PSC that integrates a CPI substrate with a nanostructured downshifting medium to enhance efficiency.
Materials and Methods
The TLS was fabricated using poly(methyl methacrylate) (PMMA) doped with Eu-complex luminophores, spin-coated on polydimethylsiloxane (PDMS)-coated glass. PSCs were built on a 50 µm-thick CPI substrate patterned with indium tin oxide (ITO) via sputtering.
A perovskite precursor solution was spin-coated on the ITO layer, followed by sequential deposition of C60 (23 nm), bathocuproine (BCP; 8 nm), and Cu (100 nm) using thermal evaporation.
PL intensities of the TLSs were analyzed using a spectrofluorophotometer with a 315 nm excitation source. PSC performance was evaluated under a full-spectrum solar simulator, calibrated with a silicon reference cell.
The external quantum efficiency (EQE) spectra of the PSCs were recorded using a commercial quantum efficiency measurement system. The monochromatic light was obtained by spectroscopic separation from a white light source. Finally, the photovoltaic performances of PSCs with various TLS configurations were examined (8 different PSCs with the same TLS).
Finite-difference time-domain (FDTD) simulations were performed to determine the optical transmission of PDMS nanostructures. For the normal incidence case, a three-dimensional simulation volume was defined with periodic boundary conditions in the x-/y-directions and a “perfectly matched layers (PML)” boundary condition in the z-direction.
Key Findings
The fabricated PSCs comprised an ITO anode, a (2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl)phosphonic acid-based hole transport layer, a methylammonium formamidinium lead iodide bromide perovskite photoactive layer, a fullerene C60 electron transport layer, a BCP hole blocking layer, and a Cu cathode.
This PSC based on a CPI substrate exhibited a power conversion efficiency (PCE) of ≈18.6 % with an open-circuit voltage of ≈1.08 V, a short-circuit current density (Jsc) of ≈21.0 mA/cm2, and a fill factor of ≈82.0 %, with minimal hysteresis. The CPI substrate effectively blocked UV light below 385 nm, with near-zero EQE in this range.
The Eu-complex in the TLS absorbed UV photons and emitted visible light at approximately 618 nm through the Stokes shift process, allowing the CPI-based PSC to utilize UV photons without degrading performance.
Additionally, the nanostructured TLS surface diffracted near-infrared and visible solar photons, increasing their path length and improving light absorption. The combination of TLS photon scattering and diffraction effects significantly enhanced the PSC’s ability to capture and use solar energy.
EQE response measurements confirmed that TLS integration improved Jsc. Since the CPI substrate blocked photons with wavelengths below 380 nm, the measured EQE in this UV range for TLS-integrated PSCs indicated photocurrent generation from downshifted photon absorption.
The nanostructured TLS outperformed the planar TLS design, showing higher EQE values across the UV, visible, and near-infrared spectrum.
Conclusion
This study demonstrated a UV-resistant, flexible PSC with improved efficiency by integrating a CPI substrate with a nanostructured TLS. The TLS minimized photon loss and enhanced light absorption through diffraction and scattering effects. The CPI-based PSC with TLS achieved a PCE increase from 18.6 % to 20.4 % while maintaining stability under UV exposure and repeated deformation.
Because the CPI substrate and TLS do not alter the electrical properties of the PSCs, this approach is compatible with various PSC material configurations, including heat-resistant materials. Future research could focus on optimizing TLS design and exploring additional downshifting materials to further improve efficiency and stability.
Journal Reference
Kim, J., et al. (2025). Ultraviolet‐Resistant Flexible Perovskite Solar Cells with Enhanced Efficiency Through Attachable Nanophotonic Downshifting and Light Trapping. Small. DOI: 10.1002/smll.202501374, https://onlinelibrary.wiley.com/doi/10.1002/smll.202501374
Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.