Luminescent Spectral Conversion to Improve the Performance of Dye-Sensitized Solar Cells

Solar spectral management for natural photosynthesis: from photonics designs to potential applications

Photosynthesis is the most important biological process on Earth that converts solar energy to chemical energy (biomass) using sunlight as the sole energy source. The yield of photosynthesis is highly sensitive to the intensity and spectral components of light received by the photosynthetic organisms. Therefore, photon engineering has the potential to increase photosynthesis. Spectral conversion materials have been proposed for solar spectral management and widely investigated for photosynthesis by modifying the quality of light reaching the organisms since the 1990s. Such spectral conversion materials manage the photon spectrum of light by a photoconversion process, and a primary challenge faced by these materials is increasing their efficiencies. This review focuses on emerging spectral conversion materials for augmenting the photosynthesis of plants and microalgae, with a special emphasis on their fundamental design and potential applications in both greenhouse settings and microalgae cultivation systems. Finally, a discussion about the future perspectives in this field is made to overcome the remaining challenges.

Improving UV stability of perovskite solar cells without sacrificing efficiency through light trapping regulated spectral modification

The stability of perovskite solar cells is an important issue to be addressed for future applications. Perovskite solar cells are vulnerable to exposure to UV light due to promoted chemical reactions. However, preventing UV light from entering solar cells lowers the power conversion efficiency by reducing the photocurrent. The challenge is to improve UV stability without sacrificing efficiency. Here, we demonstrate the reduction of UV light-related negative effects from the perspective of spectral modification. By simultaneously introducing UV-visible downshifting and light trapping, perovskite solar cells can achieve a comparable efficiency of over 21% to that of an unmodified device. The optimized device obtains increased UV stability due to UV-visible downshifting. Different from other strategies, spectral modification externally alters the composition of incident light and improves UV stability without changing the internal device architecture, which is broadly applicable to perovskite solar cells with different structures. The present work may also find applications in other types of solar cells to boost the stability of devices exposed to UV light.

Molecular engineering mechanism of organic photoactive layer by alkyl chains, 4-butoxyphenyl and cyanogroup

The three organic dye molecules (JY31, JY32 and JY33) were applied to the photoactive layer in solar cells. Photophysical and photochemical characteristic have been investigated with natural bond orbital (NBO), frontier molecular orbital, ionization potentials, electron affinities, absorption properties, reorganization energies, static first hyperpolarizability, emission characteristics, IR spectra, charge density difference; the influence of alkyl chains and 4-butoxyphenyl on properties were revealed; Subsequently, three new molecules JY33-1, JY33-2 and JY33-3 were designed by inserting the electron withdrawing group -CN into the acceptor part of JY33 in order to understand molecular engineering mechanism. The results show that the three original molecules have relatively high molar extinction coefficients, and the molecule of JY33 with a 4-butoxyphenyl group enables a bathochromic shift in absorption spectrum and is beneficial to improve the hole transport, injection capacity and ICT properties as well as better energy levels matching. The current study provides an effective channel for manipulating performance in materials design of solar cells.

Enhanced absorption and photoluminescence from dye-containing thin polymer film on plasmonic array

Thin films containing light emitters act as light-to-light converters that absorb the incident light and emit luminescence. This well-known phenomenon is photoluminescence (PL). When a photoluminescent film is notably thinner than the absorption length of emitters, it exhibits weak absorption of incident light. The absorption can be increased by depositing the thin film on a plasmonic array of metallic nanocylinders arranged with a specific periodicity. The array couples the incident light into the thin film, facilitating the plasmon-enhanced absorption by the emitters in the film. In this study, we demonstrate both experimentally and numerically the plasmon-enhanced absorption of a rhodamine 6G-containing film that is thinner than its absorption length using a periodic array of Al nanocylinders. The experimental results demonstrate that the spectrally integrated PL intensity is increased up to 3.78 times. In addition to enhanced absorption, the array is also found to diffract the PL into a direction determined by the periodicity, thereby facilitating the multiplied enhancement of PL. The combination of the two factors yields a PL intensity enhanced up to 10 times at a specific angle and wavelength. Numerical simulations combining the carrier kinetics with full-wave electromagnetics in the time-domain support the experimental observations.

Designing an efficient graphene quantum dot-filled luminescent down shifting layer to improve the stability and efficiency of perovskite solar cells by simple optical modeling

Degradation of perovskite material under UV light is a problem hampering the practical application of perovskite solar cells (PSCs) despite attaining high efficiency. This paper studies the application of a luminescent down shifting (LDS) layer containing graphene quantum dots (GQDs) on top of a PSC as an efficient strategy to improve the stability and light harvesting efficiency of PSCs under UV light. With absorption and emission bands in the UV and visible regions respectively, and simple synthesis of GQDs with a high luminescence quantum efficiency (QE), GQDs are a suitable candidate as a down shifting material in the LDS layer. Here, a simple optical model is used to investigate the effect of parameters such as the concentration of GQDs, LDS layer thickness, absorption/emission bands of GQDs and the luminescence quantum efficiency on the performance of the LDS layer. The calculated results show that application of a GQD-filled LDS layer, with 94% QE and negligible RO and PA, on a PSC causes a remarkable enhancement in the incident photon to current conversion efficiency (IPCE) and thereby the short circuit current density (J_SC) in the 300–400 nm spectral range of more than 400%. This strategy is also very effective in improving the stability of the PSC by suppressing the UV light from entering the device.

Optical modeling of a GQD-filled LDS layer on top of a perovskite solar cell (PSC) confirms GQDs as a suitable candidate as a luminescent material for application of the LDS strategy in PSCs.