# Cu-doped nanocrystal carbon dots for integrated fabrication of ultrabright luminescent solar concentrators

Mahnoor Hassan, Kassa Belay Ibrahim, Jodi Gobbo, Shujie You, Enrico Ercolini, Enrico Trave, Margherita Zavelani-Rossi, Edoardo Carraro, Andrea Iudica, Paolo Moras, et al.

► To cite this version:

Mahnoor Hassan, Kassa Belay Ibrahim, Jodi Gobbo, Shujie You, Enrico Ercolini, et al. Cu-doped nanocrystal carbon dots for integrated fabrication of ultrabright luminescent solar concentrators. Materials Today Sustainability, 2025, 32, pp.101230. 10.1016/j.mtsust.2025.101230. hal-05304071

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# Cu-doped nanocrystal carbon dots for integrated fabrication of ultrabright luminescent solar concentrators

Mahnoor Hassan<sup>a</sup>, Kassa Belay Ibrahim<sup>a,*</sup>, Jodi Gobbo<sup>a</sup>, Shujie You<sup>b</sup>, Enrico Ercolini<sup>b</sup>, Enrico Trave<sup>a</sup>, Margherita Zavelani-Rossi<sup>c,d</sup>, Edoardo Carraro<sup>c</sup>, Andrea Iudica<sup>c</sup>, Paolo Moras<sup>e</sup>, Mario Leopoldo Rivera-Salazar<sup>f,g</sup>, Stephanie Bruyere<sup>h</sup>, David Horwat<sup>h</sup>, Alberto Vomiero<sup>a,b,e,***</sup>, Elisa Moretti<sup>a,**</sup>, Tofik Ahmed Shifa<sup>a,****</sup>

## ARTICLE INFO

### Keywords:

- Carbon dots

- Transition metal doping

- Luminescence solar concentrator

- Time-resolved transient transmission

## ABSTRACT

Carbon dots (CDs) are promising fluorophores for optoelectronic devices. Yet, achieving CDs with high solid-state photoluminescence quantum yields (PLQYs) remains a significant challenge. The development of metal-doped carbon dots (CDs) to effectively modulate their electronic properties and surface chemical reactivities is still in its early stages. This work introduces copper-doping to CDs (Cu-CDs) luminescent material to modify the optoelectronic properties of CDs. The as-synthesized CDs show a Stokes shift of ≈0.67 eV and high PLQYs of 62 %. The Cu-CDs show the highest power conversion efficiency of 2.36 % compared to CDs (2.04 %) with a Stokes shift of 0.71 eV. These findings demonstrate the possibility of tuning optical properties into CDs via metal doping, obtaining eco-friendly, high-efficiency LSCs through scalable production techniques, paving the way to the lab-to-fab transition of this kind of device. Our results demonstrate that dual-emission Cu-CDs with strong solid-state fluorescence are promising candidates as luminophores in efficient photovoltaic devices.

## 1. Introduction

The prevailing reliance on conventional energy sources, particularly fossil fuels, has given rise to a host of adverse environmental consequences. The sustainable use of sunlight for renewable and clean energy production has gained significant attention, leading to the development of solar technologies [1–3]. However, achieving high solar-to-electrical power conversion efficiency (PCE) at a low cost remains a challenge for solar cells. One promising solution is the luminescent solar concentrators (LSCs), which are a large-area sunlight collector that relies on

photoluminescent materials suspended within a dielectric light guide [4–6]. These materials capture intense energy irradiance and re-emit photons at down-shifted energies into optical light guide modes, which are then light-guided to the edges of the light guide substrate. From the edges, light is then converted into electric current through small-area solar cells that are mounted at the slab edges [7,8]. This allows LSCs to collect and channel sunlight from a wide expanse, increasing conversion efficacy and reducing the surface area of expensive PV cells. LSCs have many advantages over traditional photovoltaic systems, including being inexpensive, lightweight, and

<footnote><sup>a</sup> Department of Molecular Sciences and Nano Systems, Ca' Foscari University of Venice, Via Torino 155, Mestre, Venezia, 30172, Italy</footnote>

<footnote><sup>b</sup> Division of Materials Science, Department of Engineering Sciences and Mathematics, Luleå University of Technology, Luleå, 971 87, Sweden</footnote>

<footnote><sup>c</sup> Dipartimento di Fisica, Politecnico di Milano, Piazza L. da Vinci 32, 20133, Milano, Italy</footnote>

<footnote><sup>d</sup> IFN-CNR, Piazza L. da Vinci 32, 20133, Milano, Italy</footnote>

<footnote><sup>e</sup> CNR-Istituto di Struttura Della Materia (CNR-ISM), SS 14, Km 163.5, 34149, Trieste, Italy</footnote>

<footnote><sup>f</sup> CNR-IOM, Laboratorio TASC, AREA Science Park, Basovizza, Trieste, 34149, Italy</footnote>

<footnote><sup>g</sup> Dipartimento di Fisica, Università di Trieste, Via Valerio 2, Trieste, 34127, Italy</footnote>

<footnote><sup>h</sup> Université de Lorraine, CNRS, IJL, F-54000, Nancy, France</footnote>

<footnote>* Corresponding authors.</footnote>

<footnote>** Corresponding author.</footnote>

<footnote>*** Corresponding author. Department of Molecular Sciences and Nano Systems, Ca' Foscari University of Venice, Via Torino 155, Mestre, Venezia, 30172, Italy.</footnote>

<footnote>**** Corresponding author.</footnote>

<footnote>E-mail addresses: kassabelay.ibrahim@unive.it (K.B. Ibrahim), elisa.moretti@unive.it (A. Vomiero), alberto.vomiero@ltu.se, alberto.vomiero@unive.it (E. Moretti), tofikahmed.shifa@unive.it (T.A. Shifa).</footnote>
semi-translucent, as well as having tunable optical properties [9,10].

This makes them ideal for use in building-integrated photovoltaics, where aesthetics and design are important considerations. However, there are also significant challenges that must be addressed to make LSCs practical for large-scale applications [5]. One major issue is the energy reabsorption inefficiency associated with luminescent materials, which can limit their effectiveness and practicality [11,12]. To preserve efficiency, secondary absorption and scattering at optical flaws as well as surface reflection at the light-guide surface must be reduced [13,14]. The photoluminescence quantum yield (PLQY) of the luminophore should be bordering on 100 % [15]. To reduce reabsorption losses, it should also have a large Stokes shift, a high absorption coefficient, and a wide spectral overlap with the solar spectrum [16]. To enable mass production, the light guide and luminophore should both exhibit outstanding photostability, durability, and thermal stability [14]. Despite drawbacks, ongoing research targets improved LSCs efficiency for solar applications, given their lightweight, semi-translucent, and tunable properties suitable for building integration. Overcoming reabsorption and addressing optical defects are key to scaling up LSC viability for large-scale solar energy harnessing. Stokes shift engineering and increase of PLQY are key strategies to improve LSCs functionality and make them more appealing to the market [17,18]. LSCs utilizing inorganic Quantum Dots (QDs) offer high efficiency but face challenges like limited stability due to oxidation [19] and toxicity [20] concerns with heavy metals like cadmium or lead. On the other hand, organic QDs LSCs offer tunable optical properties and lower toxicity compared to their inorganic counterparts. However, they face challenges with photostability and efficiency due to their complex synthesis and environmental sensitivity. Examples include halide-based, silicon, and carbon dots (CDs) LSCs, each with specific constraints [21,22]. Hybrid LSCs, combining different materials, emerge as a promising solution to enhance efficiency and address issues like stability and toxicity in QD-based LSCs [23,24]. CDs are gaining attention from LSCs due to their unique optical and electronic properties, including high photoluminescence quantum yield (PLQY) and strong light absorption [25]. Incorporating CDs enhances light harvesting efficiency in LSCs, offering a low-cost and non-toxic alternative to inorganic QDs [26] CDs can replace expensive photosensitizers and be tuned into their PL properties. Despite having properties like resistance to photobleaching and a wide absorption spectrum, CDs exhibit limited stability in different environments, a short luminescence lifetime, and a small Stokes shift [26–28]. These challenges are addressed through the preparation of hybrid CDs, combining technologies like metal doping to improve overall efficiency and functionality, overcoming previous limitations, and optimizing solar energy harnessing. Cu doping modifies the electronic structure of CDs, introducing defect states that tune emission, improve photoluminescence stability, and optimize energy transfer. Additionally, Cu enhances optical properties, making it beneficial for applications like LSCs [29,30].

For example, in 2017, N-doped CDs were first used in the single-layer LSCs in large-area configurations featuring a lateral dimension of 15 × 15 cm² [31]. In a notable study, Meinardi et al. synthesized silicon QDs and minimized reabsorption and scattering losses resulting in nearly optimal LSCs achieving an optical efficiency of η = 2.85 % [31]. However, this involves the use of hydrogen, argon, and helium under high pressure and extended (12 h) post-treatment, which is very expensive and complicated. Therefore, using simple methods to synthesize CDs with high PLQY for high-efficiency LSCs remains a significant challenge. Recently in 2024, Li et al., developed a one-step open-vessel synthesis method to produce barium-doped CDs (Ba-CDs) exhibiting ultrabright luminescence in both solid and liquid states. The Ba-CDs@PVP-based LSC has a PLQY of 88.78 %, showing a breakthrough optical conversion efficiency of 7.16 % and power conversion efficiency of 6.87 % under natural light irradiation (40 mW cm⁻²) [32]. Correia et al. (2023) developed an autonomous temperature sensor powered by a transparent photovoltaic (PV) system integrated into windows. The system utilized

sustainable luminescent CDs to enhance light harvesting while maintaining transparency. Their study demonstrated the potential of CDs for energy-efficient smart window applications, highlighting their role in sustainable building technologies [33]. In this work, we present high-efficiency Cu-doped carbon dots (Cu-CDs) for LSCs. The doped and undoped CDs were synthesized using the hotplate method, and the LSCs were fabricated as illustrated in Fig. 1. The photoluminescence quantum yield (PLQY) of the Cu-CDs was recorded at approximately 47 %.

## 2. Results and discussion

### 2.1. Synthesis and structure of doped and undoped CDs

TEM, HR-TEM, and XRD characterized the morphology and structure of CDs and Cu-CDs. The XRD patterns (Fig. S1a) reveal a broad peak at 34.1° and another peak at 44.5°, attributed to the (002) and (100) planes of graphitic carbon. As depicted in Fig. 2a–c, the morphology and structure of pure CDs and Cu-CDs were characterized using TEM and HR-TEM. CDs have a size distribution of 1–40 nm (average size approximately 7.82 nm) (Fig. S1b). As shown in Fig. 2a and the enlarged image (Fig. 2b), CDs exhibit lattice fringe spacings of 0.209 nm and 0.345 nm, corresponding to the (100) and (001) faces of graphite, respectively, indicating that the core of CDs has a graphite-like structure. Based on the TEM results (Fig. 2c), introducing Cu increases the CDs’ graphitization and degree of crystallinity. The increase in graphitization and crystallinity upon Cu introduction is attributed to, Cu being a well-known catalyst for graphene formation, facilitating the reorganization of carbon atoms into sp²-hybridized domains [34]. Its introduction enhances graphitization and crystallinity, while Cu atoms serve as nucleation centers, promoting the formation of graphene-like structures.

Fourier transform infrared (FTIR) spectroscopy and XPS further corroborated the structure, revealing compositional information and their possible bonds. As displayed in (Fig. S1c), the FTIR spectra recorded from as-prepared and Cu-doped CDs, are mostly identical between 4000 and 1500 cm⁻¹, the functional groups region. This indicates that metal dopants are likely incorporated into the CD matrix without significantly changing the functional groups observed in the FT-IR spectra. In the fingerprint region (1500-400 cm⁻¹), two extra peaks appear at 876 and 1082 cm⁻¹ in both as-prepared and Cu-doped CD samples, which are usually assigned to C-H and C-O vibrations, respectively. The similarity suggests that the addition of metal dopants does not significantly alter the chemical composition or surface chemistry detected by FT-IR spectroscopy, as confirmed by similar works [35]. Furthermore, a peak at 711 cm⁻¹ is present only in Cu-CDs, which can be correlated with either aromatic ring and/or coupling of Cu²⁺ with CDs. This agrees with the TEM result that the introduction of Cu results in enhancing the sp² structure in CDs. To study the surface properties of CDs, XPS measurement was performed. In the Cu-CDs 2p XPS spectrum (Fig. 2d), distinct characteristic peaks are observed at binding energies of 832.5, 472.4, 354.7, and 252.4 eV, corresponding to the presence of Cu, O, N (from the precursor), and C elements, respectively. The high-resolution Cu 2p spectra (Fig. S1d) further reveal the surface oxidation of Cu, resulting in O-M-O structures, consistent with the FT-IR spectral results.

### 2.2. Optical properties of metal-doped CDs

Ultraviolet–visible (UV–vis) absorption spectroscopy was conducted to explore the prepared samples’ optical properties, particularly the bandgap. Fig. 3a and b present the UV–vis absorption spectra of CDs and Cu-CDs LSCs respectively. The spectra indicate that CDs and Cu-CDs exhibit an absorption band in the near UV region centered around 410 nm and a strong absorption band below 300 nm. The UV–vis absorption spectroscopy for varying concentrations of Cu-CDs in PVP was also recorded (Fig. S2a). According to Yu and Wang, the absorption at
<figure><img src="image_2.png" /><figcaption>Fig. 1. Schematic representation of synthesis and fabrication of LSC to JV curve measurements for doped and undoped CDs.</figcaption></figure>

<figure><img src="image_3.png" /><figcaption>Fig. 2. HRTEM image of (a) CDs (b) enlarged image (c) Cu-CDs. XPS wide range spectra of (d) Cu 2p.</figcaption></figure>

below 300 nm is ascribed to π-π* transition of aromatic C=C bonds from
CDs core [36,37], while the band around 330 nm attributes to n-π*
transition of C=O bonds and the absorption at 410 nm is related to
surface states [38]. As illustrated in Fig. S2b and S2c, the absorption
spectra are converted into Tauc plots and fitted with γ = 1/2 (for direct
bandgap semiconductors). The calculated optical band gaps are 2.63 eV

and 2.60 eV for CDs and Cu-CDs, respectively. The steady-state PL
mapping (Fig. 3c and d) shows that both CDs and Cu-CDs are emitted in
the 450-700 nm visible range, and the emission is slightly
excitation-dependent. The most noticeable excitation/emission plot is
derived at 412/530 nm for CDs (Fig. 3c). In addition, a strong emission
peak at 530 nm (2.34 eV) when excited by an absorption band of 412 nm
<figure><img src="image_4.png" /><figcaption>Fig. 3. UV-vis absorption, PL and PLE spectra of (a) CDs and (b) Cu-CDs. Excitation-emission contour mapping of (c) CDs and (d) Cu-CDs.</figcaption></figure>

(3.01 eV), with a Stokes shift of 118 nm (0.67 eV) (Fig. 3a). In comparison, the Cu-CDs show emission at 540 nm (2.29 eV) with an absorption maximum at 410 nm (3.02 eV), corresponding to a Stokes shift of 130 nm (0.72 eV) (Fig. 3b). In Fig. S3a and b, the Commission Internationale de l'éclairage (CIE) chromatic diagram extracted from PL mapping visualizes that Cu-CDs are emitting in the blue region under UV excitation and moving towards the green region and emitting a similar color as undoped CDs when the excitation wavelength increases. The PL mapping also presents two excitation regions in deep UV light (250–290 nm) and UV-vis light (300–500 nm), with an excitation minimum in between, which coincides with a minimum absorption region in the absorption spectra of CDs at around 300 nm (Fig. 3a).

In fluorescence spectroscopy and LSC, the Stokes shift is commonly used to estimate the light-emitting related performance. However, due to the overlapping of absorption and emission spectra, part of the emitted photons is reabsorbed by the emitter itself and lowering the QY efficiency and related performance. In our work, although PLQY and TRPL characterization provided initial insights into the photophysical properties of Cu-CDs, the results alone could not fully explain the observed device performance. To gain a deeper understanding of the energy transfer dynamics and reabsorption behavior in the LSCs, we calculated the overlap integral (OI*) of the prepared samples using Eq. (6).

$$ \text{overlap integral (OI*)} = \frac{\int_{0}^{\infty} A(\lambda)PL^{*}(\lambda)d\lambda}{\int_{0}^{\infty} PL^{*}(\lambda)d\lambda} \qquad 6 $$

Where OI* represents the modified overlap integral, which depends on factors such as film thickness and emitter concentration, while PL*(λ) denotes the normalized emission spectrum of the emitter embedded in the polymer matrix. As described in the equation above, the OI represents the ratio between the integral of the absorbance, PL emission over the emission range, and the total PL emission integral, which is more accurate in evaluating the LSC's emission [16]. A higher overlap integral results in significant spectral overlap, leading to increased reabsorption

losses, reduced optical efficiency, and shorter light transport distances due to multiple absorption-emission cycles. In contrast, a lower overlap integral minimizes spectral overlaps, thereby reducing reabsorption losses, enhancing optical efficiency, and promoting a larger Stokes shift, which improves photon transport and energy capture by the solar cell [43]. Therefore, a lower overlap integral is preferred for maximizing LSC performance.

The difference between the reference and the LSC is calculated as the total absorbance. The relevant parameters for the calculation of OI* are presented in Table S3. The calculated OI* values are 0.123 for CDs-LSC with a Stokes shift of 0.67 eV, and 0.120 for Cu-CDs-LSC with a Stokes shift of 0.72 eV. This small reduction in OI* suggests that Cu doping slightly improves the optical properties by minimizing reabsorption through increased spectral separation. Although the difference is minor, it highlights the beneficial effect of doping on reducing spectral overlap, which can enhance the overall efficiency of LSCs.

The time-resolved transient transmission (ΔT/T) measurements were performed to get insights into the decay channels of the CDs and doped Cu-CDs produced by the space-confined vacuum-heating method, in PVP solution. We used the pump-probe technique with a temporal resolution of about 100 fs. We tuned the pump pulse at a central wavelength of 400 nm, resonant with the peak of absorption, while the probe was a white light continuum spanning from about 340 to 740 nm. ΔT/T data were collected at low pump fluence (70 ΔJ/cm²). The experimental map for the undoped CDs sample (Fig. S4a) reproduces the features of our previous data reported [28], characterized by a band of stimulated emission (SE), at wavelength coincident with the steady-state emission. SE appears in less than 500 fs, which means that the Stokes shift takes place on a timescale much shorter than 500 fs. SE band did not lose significant intensity for long-time delays (over the temporal window of 1 ns) consistent with the high PLQY and long PL time decay lifetime. Spectral evolution shows the formation of a photo-induced absorption (PIA) band around 460 nm, and a red-shift of the SE, consistent with thermal expansion of the CDs following the dissipation of the Stokes shift energy. We note that this phenomenon is highly
reduced for CDs produced by the hot-plate method to ones produced by space-confined vacuum heating [28]. PIA only partially affects the blue side of SE (for time delays longer than about 20 ps) and, interestingly, no other absorption channels compete with the emission which is a non-common behavior in CDs [39,40].

Cu-doping does not significantly alter the decay channels. Fig. 4a presents the ΔT/T map for Cu-CDs across the 340–700 nm probe spectral range and time delays up to 1000 ps, while Fig. 4b shows the corresponding spectra at selected time delays, and Fig. 4c illustrates the dynamics at specific probe wavelengths. In the ΔT/T spectra, two main positive bands appear: the first, centered around 410 nm, which is assigned to photo-bleaching (PB) of the ground state absorption; the second, peaked at around 530 nm, coincides with the emission spectrum and thus assigned to the stimulated emission (SE). The negative signal in the short wavelength region (around 360 nm) came from excited state absorption (ESA) to higher excited states, while that at high wavelength (>660 nm) can be ascribed to defect states. Finally, the negative signal, which emerges in about 20 ps, is similar to that obtained in Ref. [28] and thus related to thermal expansion that induces a redshift of ground state absorption. It is interesting to note that the excited state responsible for radiative emission is populated in less than 150 fs, it reaches its maximum population in ~1 ps, has a very slow decay (Fig. S4b), and covers a broad spectral range from ~480 to ~630 nm'. This highlights the emission properties characterized by an extremely fast (<150 fs) Stark effect with the formation of the broad emissive state, which out- competes any other absorption mechanism or any other form of relax- ation. Comparison between Cu-CDs and undoped CDs shows that the photo-bleaching dynamics are unaffected by doping, while the decay of the emissive state is somehow slower for Cu-CDs (Fig. S4c). Moreover, ΔT/T spectra at long time delays, normalized at the PB signal, shown in Fig. 4d, show that Cu-doping results in a higher population of the emissive state, to undoped samples.

Photoluminescence quantum yield (PLQY) and the time-resolved PL

emission (TRPL) were recorded to further understand the influence of Cu doping on CDs' performance. Fig. 5a and b show typical TPRL spectra of CDs and Cu-CDs respectively, at the maximum emission at 510 nm under 372 nm excitation from a pulsed LED. The CDs' decay curve can be fitted using a single exponential decay equation with decay time. The TRPL of Cu-CDs requires a bi-exponential model with a fast decay $\tau_1$ below 8.5 ns and a slow decay $\tau_2$ around 14 ns. To simplify the comparison, the intensity averaged decay time is introduced which considers both fast- and slow-decays and their weights. The result is summarized in Table S1. Among all the Cu-CDs samples, Cu10 %0.6 ml presents the least contribution from the fast decay, and the average decay time of 14.46 ns is nearly the longest, and close to the decay of non-doped CDs which is 14.80ns. The CD spectra are well-fitted by a single exponential decay model implying the presence of a single recombination channel. Excited electrons can then relax through these additional pathways, leading to a faster overall decay and potentially influencing the light emission properties. The PLQY of the CDs was obtained using an integrating sphere ($\lambda_{ex}$ = 405 nm) coupled to a PL spectrometer (Fig. 5c and d). For the absolute PLQY measurement, the excitation and emission of both the QD sample and reference (background without QDs) were measured to compare. As a result, the PLQY of CDs was found to be 62 %, suggesting that the selected synthesis technique can generate high-quality carbon dots and create an electronic structure that is favorable for efficient light emission. It can be seen from Table S2, Fig. S5, that the values of PLQY decrease as the concentration of Cu doping increases, and the maximum PLQY values were observed at a concentration of 0.6 % v/v. In Fig. 5c, the emission spectrum of the CDs shows a prominent peak with a PLQY of 62 %, indicated by the black line, alongside the scattering profiles from the glass substrate and the CDs themselves. In contrast, Fig. 5d presents the emission spectrum of the Cu-CDs, which demonstrates a notable difference in peak intensity and a reduced QY of 47 %, as shown by the orange line. The doping possibly modifies the surface of the CDs, resulting in changes in charge transfer and local charge distribution.

<figure><img src="image_5.png" /><figcaption>**Fig. 4.** The fs pump-probe ΔT/T measurements of Cu-CDs with a pump wavelength at 400 nm; (a) ΔT/T 2D map; (b) ΔT/T spectra at different time delays (indicated in the label), the region around 410 nm is not shown due to scattering noise; (c) ΔT/T dynamics at selected wavelengths (indicated in the label). (d) ΔT/T normalized spectra at 200 ps time delay for CDs and Cu-CDs. Inset: scheme of the electronic band structure and the population dynamics.</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>**Fig. 5.** TRPL spectrum with corresponding fitting curves of (a) CDs, and (b) Cu-CDs. PLQY spectra at excitation wavelength 405 nm for (c) CDs, and (d) Cu-CDs. Efficiency of the film LSCs based on Cu-CDs.</figcaption></figure>

These alterations may affect the process of formation and recombination of electron-hole pairs within the CDs, leading to a variation in the PL emission spectrum, which in turn lowers the QY [41]. Cu doping may also introduce non-radiative recombination centers (e.g., defects, phonon interactions, or trap states) which present in changes in TRPL spectra.

The PV cells utilized in this study are ordinary commercial cells with dimensions of 5.3 × 1.8 cm² (active area 2.5 × 0.2 cm²). PV cell information and experimental setup are described in the supplementary information along with SiPV PCE and EQE curve (Fig. S6). The functionality of the LSCs was measured according to the latest international standards [42–44].

The Fill Factor is calculated using the formula:

$$FF = \frac{V_{max} \times I_{max}}{V_{OC} \times I_{sc}} \qquad 1$$

We calculate the PCE using:

$$\eta_{PCE} = \frac{J_{sc} \times V_{oc} \times FF}{P_{in}} \qquad 2$$

Where,

$$P_{in} = E \times A \qquad 3$$

$V_{max}$ represents the maximum voltage in these equations, and $I_{max}$ denotes the maximum current. $V_{oc}$ indicates the open-circuit voltage, while $I_{sc}$ stands for the short-circuit current. The input power, $P_{in}$, is determined by the product of the incident light power per unit area, denoted by $E$ (irradiance), and the area of the top surface of LSC, represented by $A$.

The photovoltaic parameters such as $V_{oc}$, $J_{sc}$, FF, and $\eta_{PCE}$ for the film LSCs of SiPV, PVP, CDs, and Cu-CDs are listed in Table 1. The film-structured LSCs based on CDs (Fig. 6a) are translucent but the

<table><caption>**Table 1**

Photovoltaic parameters of doped and undoped CDs.</caption><thead><tr><th>Sample</th><th>J<sub>sc</sub><br>(mA/cm<sup>2</sup>)</th><th>V<sub>oc</sub><br>(V)</th><th>FF<br>(%)</th><th>G<br>(%)</th><th>η<sub>opt</sub><br>(%)</th><th>η<sub>PCE</sub><br>(%)</th></tr></thead><tbody><tr><td>SiPV</td><td>23.26</td><td>0.48</td><td>55.4</td><td>12.5</td><td>–</td><td>6.27 ± 0.52</td></tr><tr><td>PVP</td><td>0.12</td><td>0.39</td><td>31.7</td><td>12.5</td><td>0.56 ± 0.19</td><td>0.26 ± 0.06</td></tr><tr><td>CDs</td><td>0.60</td><td>0.44</td><td>48.5</td><td>12.5</td><td>2.56 ± 0.16</td><td>2.04 ± 0.05</td></tr><tr><td>Cu-CDs</td><td>0.67</td><td>0.45</td><td>49.1</td><td>12.5</td><td>2.86 ± 0.22</td><td>2.36 ± 0.07</td></tr></tbody></table>

transparency decreases with the increase of CD concentrations, while the Luminescent Solar Concentrator words at the bottom are still clearly visible. Similarly, Fig. 6b displays photographs of CDs and Cu-CDs taken under solar simulator. The LSCs utilizing CD/PVP and Cu-CD/PVP thin films exhibit bright green edge emissions at the edges. Accordingly, the current-voltage characteristics were measured and depicted in Fig. 6c and d. The current density measured is 0.60, 0.67, and 0.49 mA/cm² for CDs, and Cu-CDs, respectively, indicating that after doping, the efficiency of Cu-CDs increases. For comparison, the efficiency of our solar cell (SiPV) was also calculated, which was found to be around 6.27 %. To further assess the impact of the coating, a float glass of the same size, coated solely with PVP was also prepared, and measured its efficiency. This allowed us to evaluate the effectiveness of the PVP coating on its own. These calculations show that the Cu-CDs solar cell exhibited the highest efficiency at 2.36 %, while the CDs solar cells showed efficiencies of 2.04 %. The differences in efficiency can be attributed to the variations in their $V_{max}$, $I_{max}$, $V_{oc}$, and $J_{sc}$ values, which directly influence Pmax and subsequently the fill factor and overall efficiency of the solar cells. Furthermore, PCE measures how efficiently a device, like a solar cell, converts incident light into electrical energy, while external optical efficiency specifically measures how effectively the device captures and utilizes incident light, including how well it minimizes losses like
<figure><img src="image_7.png" /><figcaption>Fig. 6. (a) Photographs of the LSC film based on CDs under natural sunlight (b) Photographs of the CD, and Cu-CDs under solar simulator. (c) IV curve of Solar cells, (d) JV curve of doped and undoped CDs.</figcaption></figure>

reflection or scattering.

The external optical efficiency is calculated as follows [6].

$$ \eta_{opt} = \frac{I_{LSC}}{I_{SC} \times G} \times 100 \% \qquad 4 $$

where G is given by:

$$ G = \frac{A_{top}}{A_{edge}} \qquad 5 $$

In these equations, $\eta_{opt}$ denotes the external optical efficiency of the luminescent solar concentrator. $I_{LSC}$ represents the light signal collected by the luminescent solar concentrator, while $I_{SC}$ is the short-circuit current, which is the maximum current the device can produce when the voltage is zero. The term G is the geometric factor, $A_{top}$ is the illuminated area of LSC, and $A_{edge}$ is the area of the edge surface where the solar cell is placed. The external optical efficiencies were 2.56 % for CDs and 2.86 % for Cu-CDs. The best values of $V_{oc}$, and $J_{sc}$ are obtained at 0.45 V, and 0.67 mA/cm², respectively, for Cu-CDs. These values indicate that Cu-CDs exhibit higher efficiency because there is less overlap between their absorption and emission spectra which reduces the chances of reabsorption and non-radiative losses. This intrinsic behavior of CDs plays a crucial role in determining the overall efficiency of the LSC, leading to higher power conversion efficiency compared to other materials [45]. This study represents a significant advancement by introducing a novel approach employing Cu-CDs for LSC applications. Firstly, Cu-CDs were synthesized through a straightforward one-step hot plate method. This synthesis route is characterized by its simplicity and absence of vacuum reaction conditions, suggesting its potential for large-scale production of Cu-CDs suitable for practical applications. Secondly, the findings reveal that CDs exhibit a high PLQY exceeding 60 %, surpassing that of CDs-PLMA with PLQY 30 %, rendering them more suitable for integration into luminescent solar concentrators.

## 3. Conclusion

In summary, we have demonstrated a facile route to prepare highly luminescent, low-cost, and solution-processable Cu-CDs, which can be well dispersed in multiple organic polar solvents. Transparent thin-film LSCs were obtained after the CDs were mixed with PVP polymer and drop-cast on glass. The CDs exhibit a significant Stokes shift of 0.67 eV (PLQY = 62 %, $\text{OI}^* = 0.123$), along with excellent solubility in organic polar solvents. Whereas the Cu-CDs exhibit a Stokes shift of 0.72 eV (PLQY = 47 %, $\text{OI}^* = 0.120$). Due to the absence of reabsorption loss, the transparent LSCs based on Cu-CDs achieve $\eta_{opt}$ of 2.86 % and a $\eta_{PCE}$ of 2.36 % after coupling to PV cells. This suggests that Cu doping not only enhances the Stokes shift and reduces the overlap integral, thereby minimizing reabsorption losses, but also enables more efficient light harvesting and energy conversion in transparent LSCs, despite a slightly lower PLQY. In the PVP solution, we performed time-resolved transient transmission ($\Delta T/T$) measurements to get insights into the decay channels of the CDs and doped CDs produced by the space-confined vacuum-heating method. These LSCs show good stability both in the atmosphere and under exposure to light and elevated temperatures. Our work indicates that the Cu-CDs have great potential for applications in large areas, low-cost, and high-efficiency LSCs.

## 4. Experimental section

### 4.1. Materials

Urea ($CH_4N_2O$), citric acid ($HO_2CCH_2C(OH) (CO_2H)$, $CH_2CO_2H$, >99.0 %), calcium chloride ($CaCl_2$), copper chloride dihydrate ($CuCl_2 2H_2O$, >99.0 %) were obtained from Sigma Aldrich - Life Sciences (Switzerland). The chemical reagents were not further purified but were used as received. Microscopic glass slides were used. To cast the glass, two polymers were used: one of which was polyvinylpyrrolidone K 90 ($C_6H_9NO$) from Sigma Aldrich - Life Sciences (Switzerland) and the
other was polyvinylpyrrolidone K 30 from Thermo Fisher Scientific. Methanol (CH₄O) was used as a solvent and was acquired from Sigma Aldrich - Life Sciences (France), and ethanol absolute (>99.7 %) was obtained from VWR Chemicals. The chemical reagents were not further purified but were used as received.

## 4.2. Synthesis procedure

The CDs were prepared using a hot plate method on a hot plate. Initially, 5 mL of distilled water was combined with 3 g of urea, 1.5 g of citric acid, and 1 g of CaCl₂, and sonicated for 10 min. This mixture was then heated to 120 °C for 30 min with continuous stirring. Subsequently, the temperature gradually increased to 180 °C and maintained it for 20 min. Finally, the temperature further increased to 250 °C and held for 0.5–1 h while stirring. Upon drying, the sample was dispersed in ethanol and subjected to 10 min of sonication followed by centrifugation at 4500 rpm for 10 min to obtain a purified CD solution. The same procedure was followed for Cu-doped CDs. But, first, the precursors of CuCl₂ 2H₂O were reduced using NaBH₄ after which they were incorporated into the solution with all the precursors and followed the same heating procedure. It should be noted that this method of synthesizing CDs is repeatable.

## 4.3. LSCs fabrication

The thin film is prepared by drop casting method. Specifically, the CDs ethanol solutions (0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 mL) at a concentration of 0.10, 0.30, and 0.50 mg/mL were mixed with 3 mL of PVP methanol solution (100 mg/mL PVP K30 and 100 mg/mL PVP K90), respectively. The mixture was then stirred for 10 min to obtain a homogeneous solution and let rest for 5 min to remove any bubbles from the solution. The float glass with a size of 2.5 x 2.5 × 0.1 cm³ was polished at the edges, followed by ultrasonic cleaning with acetone, deionized water, and ethanol for 1 h. Approximately, 600 µL of solution was then applied dropwise to a glass surface and dried at room temperature until the methanol evaporated completely.

## 4.4. Characterization

The morphology of CDs was investigated using transmission electron microscopy (TEM) performed on a JEM-2100 F TEM (JEOL, Japan). Fourier transform infrared (FT-IR) spectra were recorded on a Vertex 70v FT-IR spectrometer (Bruker, Germany) to analyze the chemical structure and functional groups of the CDs. X-ray diffraction (XRD) patterns were obtained using a PW1050/37 diffractometer (Philips, Netherlands) to determine the crystallinity and crystal structure of the CDs. XPS was performed to determine chemical compositions in a dedicated chamber of the NFFA UHV MBE-cluster system to investigate the surface chemistry and elemental composition of the CDs. UV-visible absorption spectra of the CDs were measured in film using a UV-Vis spectrophotometer (Agilent-Cary 5000) to study their optical properties. Photoluminescence (PL) spectra, photoluminescence quantum yield (PLQY), and time-resolved photoluminescence (TRPL) measurements of both doped and undoped CDs were performed at room temperature using a fluorescence spectrometer (Edinburgh Instruments FLS980, Luleå, Sweden). The PLQY spectra was recorded using an integrating sphere under 405 nm excitation, corresponding to the wavelength of maximum absorption of the samples. TRPL measurements were conducted using an EPL-375 ps pulsed diode laser (Edinburgh Instruments). The photovoltaic properties of LSCs incorporating were evaluated using a solar simulator (10500, Abet Technologies, Inc.) calibrated to an intensity of 100 mWcm⁻² (1 sun) with a calibrated silicon solar cell. The LSCs had a surface area of 2.5 × 2.5 cm² with relatively uniform thickness. Edge emission from the light guide edges, which were not blackened, was collected and analyzed.

## CRediT authorship contribution statement

**Mahnoor Hassan:** Writing – original draft, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. **Kassa Belay Ibrahim:** Writing – review & editing, Supervision, Methodology, Investigation, Conceptualization. **Jodi Gobbo:** Methodology, Formal analysis, Data curation. **Shujie You:** Validation, Formal analysis, Data curation. **Enrico Ercolini:** Investigation, Data curation. **Enrico Trave:** Validation, Formal analysis, Data curation. **Margherita Zavelani-Rossi:** Validation, Formal analysis, Data curation. **Edoardo Carraro:** Visualization, Formal analysis, Data curation. **Andrea Iudica:** Validation, Formal analysis, Data curation. **Paolo Moras:** Validation, Data curation. **Mario Leopoldo Rivera-Salazar:** Validation, Data curation. **Stephanie Bruyere:** Validation, Formal analysis, Data curation. **David Horwat:** Validation, Formal analysis, Data curation. **Alberto Vomiero:** Writing – review & editing, Supervision, Project administration, Funding acquisition. **Elisa Moretti:** Writing – review & editing, Resources, Project administration, Funding acquisition. **Tofik Ahmed Shifa:** Writing – review & editing, Supervision, Project administration, Funding acquisition.

## Contributions

M.H., J.G., investigation, M.H. write up, A.V., K.B.I., T.A.S., and E.M. supervised and edited the manuscript. S.Y., E. E., E.T., Measure the photoluminescence, S.B., D.H., TEM characterization, P.M., M. L. R-S., XPS characterization, and M.Z-R., E. C., A.I., Pump-Probe measurement.

## Declaration of competing interest

The authors declare no competing financial or personal interests that could influence the work reported in this manuscript.

## Acknowledgments

This work was supported by the Kempe Foundation, the Knut och Alice Wallenberg Foundation (grant number KAW 2016.346), and the ÅFORSK Foundation. The authors would also like to acknowledge Ca' Foscari University of Venice for the SPIN2019 project, P. M. acknowledged partial support through the project EUROFEL-ROADMAP ESFRI of the Italian MUR. This work has been partially performed in the framework of the Nanoscience Foundry and Fine Analysis (NFFA-MUR Italy Progetti Internazionali) facility and Mr. Tiziano Finotto from the Department of Molecular Sciences and Nanosystems, Ca' Foscari University of Venice, Italy for support on the XRD measurement. Finally, T. A. Shifa acknowledged the MSCA-IF-2020, CoCaWS, 101027930, and PRIN 2022, CUP: H53D23003840001, and K.B. Ibrahim acknowledged the PNRR RTD A. M.Z.-R., E.C., and A.V. acknowledged financial support by the European Union-NextGenerationEU Programme, the National Recovery and Resilience Plan (NRRP), Mission 4 Component 2 Investment 1.1 PRIN 2022 PNRR Ministero dell'Università e della Ricerca (MUR), CUP D53D23019400001, ID P2022RL4TR "All-oxide nanowire plasmonic solar cells (NanoSolar)".

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.mtsust.2025.101230.

## Data availability

The data that has been used is confidential.
## References

[1] Z. Li, X. Xu, X. Sheng, P. Lin, J. Tang, L. Pan, Y. Yamauchi, Solar-powered sustainable water production: state-of-the-art technologies for sunlight-energy-water nexus, ACS Nano 15 (8) (2021) 12535-12566.

[2] Q. Li, M. Zhou, M. Yang, Q. Yang, Z. Zhang, J. Shi, Induction of long-lived room temperature phosphorescence of carbon dots by water in hydrogen-bonded matrices, Nat. Commun. 9 (1) (2018) 734.

[3] D. Cambié, J. Dobbelaar, P. Riente, J. Vanderspikken, C. Shen, P.H. Seeberger, T. Noël, Energy-efficient solar photochemistry with luminescent solar concentrator based photomicroreactors, Angew. Chem. Int. Ed. 58 (40) (2019) 14374-14378.

[4] F. Meinardi, F. Bruni, S. Brovelli, Luminescent solar concentrators for building-integrated photovoltaics, Nat. Rev. Mater. 2 (12) (2017) 1-9.

[5] B.S. Richards, I.A. Howard, Luminescent solar concentrators for building integrated photovoltaics: opportunities and challenges, Energy Environ. Sci. 16 (8) (2023) 3214-3239.

[6] M.G. Debije, P.P. Verbunt, Thirty years of luminescent solar concentrator research: solar energy for the built environment, Adv. Energy Mater. 2 (1) (2012) 12-35.

[7] I. Papakonstantinou, M. Portnoi, M.G. Debije, The hidden potential of luminescent solar concentrators, Adv. Energy Mater. 11 (3) (2021) 2002883.

[8] H. Hernandez-Noyola, D.H. Potterveld, R.J. Holt, S.B. Darling, Optimizing luminescent solar concentrator design, Energy Environ. Sci. 5 (2) (2012) 5798-5802.

[9] X. Gong, S. Zheng, X. Zhao, A. Vomiero, Engineering high-emissive silicon-doped carbon nanodots towards efficient large-area luminescent solar concentrators, Nano Energy 101 (2022) 107617.

[10] X. Liu, D. Benetti, J. Liu, L. Jin, F. Rosei, Color-tunable multilayered laminated luminescent solar concentrators based on colloidal quantum dots, Nano Energy 111 (2023) 108438.

[11] I. Coropceanu, M.G. Bawendi, Core/shell quantum dot based luminescent solar concentrators with reduced reabsorption and enhanced efficiency, Nano Lett. 14 (7) (2014) 4097-4101.

[12] D.M. de Clercq, S.V. Chan, J. Hardy, M.B. Price, N.J. Davis, Reducing reabsorption in luminescent solar concentrators with a self-assembling polymer matrix, J. Lumin. 236 (2021) 118095.

[13] L. Liao, T. Lin, X. Bin, K. Quan, L. Zhang, R. Zeng, J. Zhao, Reabsorption-free luminescent solar concentrator based on environmentally friendly cesium copper halide nanocrystals, J. Lumin. 248 (2022) 118927.

[14] B. Zhang, G. Lyu, E.A. Kelly, R.C. Evans, Förster resonance energy transfer in luminescent solar concentrators, Adv. Sci. 9 (23) (2022) 2201160.

[15] Y. Zhou, D. Benetti, X. Tong, L. Jin, Z.M. Wang, D. Ma, F. Rosei, Colloidal carbon dots based highly stable luminescent solar concentrators, Nano Energy 44 (2018) 378-387.

[16] C. Yang, J. Zhang, W.T. Peng, W. Sheng, D. Liu, P.S. Kuttipillai, R.R. Lunt, Impact of Stokes shift on the performance of near-infrared harvesting transparent luminescent solar concentrators, Sci. Rep. 8 (1) (2018) 16359.

[17] F. Corsini, A. Nitti, E. Tatsi, G. Mattioli, C. Botta, D. Pasini, G. Griffin, Large-area semi-transparent luminescent solar concentrators based on large Stokes shift aggregation-induced fluorinated emitters obtained through a sustainable synthetic approach, Adv. Opt. Mater. 9 (16) (2021) 2100182.

[18] R. Mazzaro, A. Vomiero, The renaissance of luminescent solar concentrators: the role of inorganic nanomaterials, Adv. Energy Mater. 8 (33) (2018) 1801903.

[19] H. Moon, C. Lee, W. Lee, J. Kim, H. Chae, Stability of quantum dots, quantum dot films, and quantum dot light-emitting diodes for display applications, Adv. Mater. 31 (34) (2019) 1804294.

[20] V.G. Reshma, P.V. Mohanan, Quantum dots: applications and safety consequences, J. Lumin. 205 (2019) 287-298.

[21] N.K. Kumawat, D. Gupta, D. Kabra, Recent advances in metal halide-based perovskite light-emitting diodes, Energy Technol. 5 (10) (2017) 1734-1749.

[22] Z. Zhu, Y. Zhai, Z. Li, P. Zhu, S. Mao, C. Zhu, Y. Lin, Red carbon dots: optical property regulations and applications, Mater. Today 30 (2019) 52-79.

[23] T. Wei, L. Wang, C. Sun, D. Xu, J. Tao, H. Zhang, W. Bi, Eco-friendly and efficient luminescent solar concentrators based on a copper (I)-Halide composite, ACS Appl. Mater. Interfaces 13 (47) (2021) 56348-56357.

[24] Y. Wang, Y. Liu, G. Xie, J. Chen, P. Li, Y. Zhang, H. Li, Highly luminescent and stable organic-inorganic hybrid films for transparent luminescent solar concentrators, ACS Appl. Mater. Interfaces 14 (4) (2022) 5951-5958.

[25] Y. Han, X. Zhao, A. Vomiero, X. Gong, H. Zhao, Red and green-emitting biocompatible carbon quantum dots for efficient tandem luminescent solar concentrators, J. Mater. Chem. C 9 (36) (2021) 12255-12262.

[26] J. Li, H. Zhao, X. Zhao, X. Gong, Boosting efficiency of luminescent solar concentrators using ultra-bright carbon dots with large Stokes shift, Nanos. Horiz 8 (1) (2023) 83-94.

[27] B. Wang, Y. Yu, H. Zhang, Y. Xuan, G. Chen, W. Ma, J. Yu, Carbon dots in a matrix: energy-transfer-enhanced room-temperature red phosphorescence, Angew. Chem. 131 (51) (2019) 18614-18619, 4.

[28] H. Zhao, G. Liu, S. You, F.V. Camargo, M. Zavelani-Rossi, X. Wang, X. Gong, Gram-scale synthesis of carbon quantum dots with a large Stokes shift for the fabrication of eco-friendly and high-efficiency luminescent solar concentrators, Energy Environ. Sci. 14 (1) (2021) 396-406.

[29] Y. Duan, Y. Huang, S. Chen, W. Zuo, B. Shi, Cu-doped carbon dots as catalysts for the chemiluminescence detection of glucose, ACS Omega 4 (6) (2019) 9911-9917.

[30] D. Zhao, Y. Huang, H. Ouyang, B. Shi, S. Li, S. Chen, S. Zhao, Facile preparation of Cu-doped carbon dots for naked-eye discrimination of phenylenediamine isomers and highly sensitive ratiometric fluorescent detection of H2O2, Talanta 239 (2022) 123110.

[31] F. Meinardi, S. Ehrenberg, L. Dhamo, F. Carulli, M. Mauri, F. Bruni, S. Brovelli, Highly efficient luminescent solar concentrators based on earth-abundant indirect-bandgap silicon quantum dots, Nat. Photonics 11 (3) (2017) 177-185.

[32] J. Li, H. Zhao, X. Zhao, X. Gong, High-efficiency luminescent solar concentrators based on carbon dots with simultaneously ultrabright solid-state and liquid-state luminescence, Adv. Funct. Mater. (2024) 2404473.

[33] S.F. Correia, L. Fu, L.M. Dias, R.F. Pereira, V. de Zea Bermudez, P.S. André, R. A. Ferreira, An autonomous power temperature sensor based on window-integrated transparent PV using sustainable luminescent carbon dots, Nanoscale Adv. 5 (13) (2023) 3428-3438.

[34] S. Bae, H. Kim, Y. Lee, X. Xu, J.S. Park, Y. Zheng, S. Iijima, Roll-to-roll production of 30-inch graphene films for transparent electrodes, Nat. Nanotechnol. 5 (8) (2010) 574-578.

[35] C. He, P. Xu, X. Zhang, W. Long, The synthetic strategies, photoluminescence mechanisms and promising applications of carbon dots: current state and future perspective, Carbon 186 (2022) 91-127.

[36] P. Yu, X. Wen, Y.R. Toh, J. Tang, Temperature-dependent fluorescence in carbon dots, J. Phys. Chem. C 116 (48) (2012) 25552-25557.

[37] Y. Wang, S. Kalytchuk, Y. Zhang, H. Shi, S.V. Kershaw, A.L. Rogach, Thickness-dependent full-color emission tunability in a flexible carbon dot ionogel, J. Phys. Chem. Lett. 5 (8) (2014) 1412-1420.

[38] C.J. Reckmeier, Y. Wang, R. Zboril, A.L. Rogach, Influence of doping and temperature on solvatochromic shifts in optical spectra of carbon dots, J. Phys. Chem. C 120 (19) (2016) 10591-10604.

[39] L. Sui, W. Jin, S. Li, D. Liu, Y. Jiang, A. Chen, M. Jin, Ultrafast carrier dynamics of carbon nanodots in different pH environments, Phys. Chem. Chem. Phys. 18 (5) (2016) 3838-3845.

[40] A. Sciortino, A. Cannizzo, F. Messina, Carbon nanodots: a review—from the current understanding of the fundamental photophysics to the full control of the optical response, C 4 (4) (2018) 67.

[41] F. Gao, J. Huang, Y. Ruan, H. Li, P. Gong, F. Wang, Y. Jiang, Unraveling the structure transition and peroxidase mimic activity of copper sites over atomically dispersed copper-doped carbonized polymer dots, Angew. Chem. Int. Ed. 62 (7) (2023) e202214042.

[42] C. Yang, H.A. Atwater, M.A. Baldo, D. Baran, C.J. Barile, M.C. Barr, R.R. Lunt, Consensus statement: standardized reporting of power-producing luminescent solar concentrator performance, Joule 6 (1) (2022) 8-15.

[43] C. Yang, D. Liu, R.R. Lunt, How to accurately report transparent luminescent solar concentrators, Joule 3 (12) (2019) 2871-2876.

[44] C. Li, Y. Gao, Z. Ren, S. Xiong, C. Li, J. Wu, J. Wang, Highly efficient, ultra-stable multi-interlayer luminescent solar concentrators based on green and red-emitting perovskite nanocrystal composites, J. Mater. Chem. C 13 (2) (2025) 945-953.

[45] Y. Zhou, D. Benetti, Z. Fan, H. Zhao, D. Ma, A.O. Govorov, F. Rosei, Near infrared, highly efficient luminescent solar concentrators, Adv. Energy Mater. 6 (11) (2016) 1501913.