Light losses from scattering in luminescent solar concentrator waveguides

Quantum Dot-based Luminescent Solar Concentrators Fabricated through the Ultrasonic Spray-Coating Method

Luminescent solar concentrators (LSCs) are a class of wave-guiding devices that can harvest solar light and concentrate it to targeted smaller areas. When coupled with photovoltaic devices (PVs), LSCs hold the potential to be integrated into various application setups, especially for building facade integration toward net-zero-energy buildings. Developing reliable LSC fabrication methods with easy scalability, high adaptability, and device controllability has been an important research topic. In this work, we report an ultrasonic nebulization-assisted spray deposition technique to fabricate quantum dot (QD)-based LSCs (QD-LSCs). This method allows for the production of high-performance QD-LSCs with different device dimensions and geometries. In addition, the quality of the QD thin-film coating layer is relatively independent of the concentration and volume of the coating QD ink solution, allowing for deliberate programming and performance optimization of the resulting QD-LSC devices. We anticipate that this ultrasonic spray coating method can be widely applied to the manufacturing of high-quality LSC devices that are integrable to various applications.

Large area stimulated emission luminescent solar concentrators modelled using detailed balance consistent rate equations

Stimulated emission luminescent solar concentrators (SELSCs) have the potential to reduce escape cone losses in luminescent solar concentrators (LSCs). However, a functional SELSC is yet to be demonstrated. Previous numerical studies and detailed balance limits provide guidance, but they also contradict and likely overestimate performance and underestimate requirements. In this work, we introduce a rate-equation model with inversion requirements compatible with detailed balance limits and apply this model to the numerical modelling of window-sized SELSCs. We find that the optimal pump photon energy for both LSCs and SELSCs is 1.35 eV and the potential improvement of SELSCs over LSCs is found to be 19.3%. The efficiencies found are much lower than those specified in previous work due to the increase in Stokes shift required for a highly luminescent material. We also find that SELSCs are more attractive at higher matrix losses, that emission linewidths <0.05  eV are desirable, and that SELSC devices can potentially achieve performance equal to LSCs at low illumination levels and simultaneously exceed it by up to 16.5% at 1-sun illumination.

Highly Efficient Luminescent Solar Concentrators Based on Benzoheterodiazole Dyes with Large Stokes Shifts

Five extended π-conjugated systems with electron donor (D) and acceptor (A) moieties have been synthesized. Their basic D-A-D structural motif is a benzothiadiazole unit symmetrically equipped with two thiophene rings (S2T). Its variants include 1) the same molecular framework in which sulfur is replaced by selenium (Se2T), also with four thiophene units (Se4T) and 2) a D'-D-A-D system having a N-carbazole donor moiety at one end (CS2T) and a D'-D-A-D-A' array with a further acceptor carbonyl unit at the other extremity (CS2TCHO). The goal is taking advantage of the intense luminescence and large Stokes shifts of the five molecules for use in luminescent solar concentrators (LSCs). All of them exhibit intense absorption spectra in the UV/Vis region down to 630 nm, which are fully rationalized by DFT. Emission properties have been studied in CH₂ Cl₂ (298 and 77 K) as well as in PMMA and PDMS matrices, measuring photoluminescence quantum yields (up to 98 %) and other key optical parameters. The dye-PMMA systems show performances comparable to the present state-of-the-art, in terms of optical and external quantum efficiencies (OQE=47.6 % and EQE=31.3 %, respectively) and flux gain (F=10.3), with geometric gain close to 90. LSC devices have been fabricated and tested in which the five emitters are embedded in PDMS and their wave-guided VIS luminescence feeds crystalline silicon solar cells.

Artificial compound eye-tipped optical fiber for wide field illumination

In this Letter, we present a novel, to the best of our knowledge, component with beam delivering and wide field beam homogenizing functions by grafting an artificial compound eye (ACE) micro-structure onto the polymer optical fiber (POF) end face. The 3D ACE mold is fabricated by femtosecond laser-assisted micro machining, and the ACE micro-structure is transferred onto the end face through high accuracy nano-imprinting. The resultant POF end face integrates over 400 spherical micro-lenses, enabling a 40% enhancement in both the acceptance angle and the effective numerical aperture. Meanwhile, the integrated ommatidia array serves as an outstanding beam homogenizer, shaping the output beam into quasi flat-top distribution, which demonstrates promise in wide field homogeneous illumination, by reflection and transmission imaging experiments in both visible and near infrared bands.