CHENG Zhanlin¹ ，ZHANG Huixin¹ ，ZHANG Xinyu^1，2，ZHANG Lei¹ ，HONG Wenpeng¹ ，LI Haoran¹

1. School of Energy and Power Engineering， Northeast Electric Power University， Jilin 132002， China；

2. College of Energy and Power Engineering， Nanjing University of Aeronautics and Astronautics， Nanjing 210016， China

Abstract

Objective Hydrophilic hydrogels are essential in evaporative cooling applications. By utilizing waste heat generated by solar cells, the hydrogels can drive internal moisture evaporation and reduce their operating temperature. However, the inherently low thermal conductivity often limits their cooling effectiveness. To address this limitation, thermally conductive fillers such as carbon nanoparticles can be incorporated into hydrogel matrices to enhance both thermal transport and moisture regulation. Carbon nanomaterials, known for their exceptional nanoscale thermal conductivity, offer a promising approach to enhancing hydrogel performance. This incorporation not only enhances the thermal conductivity of the hydrogel but also modulates its microstructure, optimizing its moisture absorption-desorption characteristics. In this study, a series of carbon nanoparticle-doped hydrogels were developed, and their moisture absorption-desorption properties were analyzed to evaluate their potential for passive cooling in solar cells.

Methods To evaluate the moisture management performance of hydrogels, samples with five different mass fractions of carbon nanoparticles were synthesized and tested (S1-5). Moisture absorption tests were conducted in a constant temperature and humidity chamber (25 ℃), where changes in hydrogel mass were recorded over time. Desorption tests were then performed in a still air laboratory environment, where the doped hydrogels were applied as cooling layers on solar panels and illuminated by a solar simulator. A precision electronic balance continuously measured the hydrogel mass during evaporation, while thermocouples monitored the back-surface temperature of the solar cells. In addition, an electrochemical workstation was used to monitor the current-voltage (I-V) characteristics of the solar cells. Data analysis and visualization were performed using Origin software to quantitatively evaluate the cooling performance of each hydrogel sample. This comprehensive evaluation aimed to determine how carbon nanoparticle doping enhances the evaporative cooling efficiency of hydrogels for photovoltaic applications.

Results and Discussion The results showed that S5 exhibited the highest moisture absorption capacity. Under standard illumination conditions, the desorption capacity was significantly enhanced in hydrogel samples doped with carbon nanoparticles. Among them, S2 demonstrated the best desorption and cooling performance. To further explore the cooling performance, key performance parameters of the solar cells were tested. In real hydrogel applications, the open-circuit voltage increased by approximately 30 mV, the fill factor improved by 4. 58%, and the energy conversion has increased by 0. 41%.

Conclusion This study develops and evaluates carbon nanoparticle-doped hydrogels for the passive cooling of solar cells. The hydrogel containing 20% carbon nanoparticles shows the highest water absorption capacity, while the sample with 5% carbon nanoparticles exhibits the most favorable desorption and cooling performance. The introduction of carbon nanoparticles significantly improves the hydrogel’s moisture absorption-desorption efficiency and accelerates water evaporation, thereby improving the passive heat dissipation capacity of solar cells.

Keywords：solar cell; passive cooling; carbon nanoparticle; hydrogel; atmospheric water harvesting; evaporative cooling

DOI：10.13732/j.issn.1008-5548.2025.04.012