# Performance Maintenance of Dye-Sensitized Solar Cells Using a Latent Heat Storage Material

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## Abstract

Recently, there has been considerable interest in various renewable energies. Among them, solar cell production has increased markedly because the photovoltaic is a clean and safe power generation method. The dye-sensitized solar cell (DSSC) has attracted much attention as an alternative to silicon solar cells due to lower manufacturing costs and plentiful resources for DSSC production. However, the performance of DSSCs has been limited by their durability and low photoelectric conversion efficiency. Temperature control of DSSCs via phase-change materials (PCMs) is expected to improve performance. In this study, DSSCs were heated or cooled with a heat exchanger copper block that was in contact with a PCM (heptadecane), while being irradiated by a solar simulator light source. The durability and photoelectric conversion efficiency of the DSSC improved under PCM temperature control.

## Keywords

Durability Dye-sensitized solar cell Phase-change material Photoelectric conversion efficiency Solar irradiance## List of symbols

- \(A_{\mathrm{area}}\)
Area of DSSC \((\hbox {m}^{2})\)

*Cp*Specific heat \((\hbox {J}{\cdot }\hbox {kg}^{-1}{\cdot }\hbox {K}^{-1})\)

*h*Heat transfer coefficient \((\hbox {W}{\cdot }\hbox {m}^{-2}{\cdot }\hbox {K}^{-1})\)

*I*Current (A)

- \(I_{\underline{sc}}\)
Short-circuit current (A)

- \(I_{\mathrm{max}}\)
Current at \(P_{\mathrm{max}}\) (A)

*K*Overall heat transfer coefficient \((\hbox {W}{\cdot }\hbox {m}^{-2}{\cdot }\hbox {K}^{-1})\)

- \(P_{\mathrm{in}}\)
Input solar energy (W)

- \(P_{\mathrm{max}}\)
Maximum generated electric power of DSSC (W)

*q*Heat flux \((\hbox {W}{\cdot }\hbox {m}^{-2})\)

*V*Voltage when \(I = 0 \hbox { A}\) (V)

- \(V_{\underline{oc}}\)
Open-circuit voltage (V)

- \(V_{\mathrm{max}}\)
Voltage at \(P_{\mathrm{max}}\) (V)

*L*Latent heat \((\hbox {kJ}{\cdot }\hbox {kg}^{-1})\)

- \(L_{\mathrm{in}}\)
Input irradiance \((\hbox {W}{\cdot }\hbox {m}^{-2})\)

*S*Solar irradiance \((\hbox {W}{\cdot }\hbox {m}^{-2})\)

*t*Time (h)

- \(T_{\mathrm{A}}\)
Ambient temperature \(({^{\circ }}\hbox {C})\)

- \(T_{\mathrm{D}}\)
DSSC temperature \(({^{\circ }}\hbox {C})\)

- \(T_{\mathrm{m}}\)
Melting temperature \(({^{\circ }}\hbox {C})\)

## Greek Letters

- \(\alpha _{\mathrm{D}}\)
Absorptivity of DSSC (–)

- \(\varepsilon \)
Emissivity (–)

- \(\eta \)
Photoelectric conversion efficiency (%)

- \(\eta _{25^{\circ }{\mathrm{C}}}\)
Photoelectric conversion efficiency at \(T_\mathrm{D} = 25\,{^{\circ }}\hbox {C}\) (%)

- \(\eta _{\mathrm{i}}\)
Initial photoelectric conversion efficiency (%)

- \(\lambda \)
Thermal conductivity \((\hbox {W}{\cdot } \hbox {m}^{-1}{\cdot } \hbox {K}^{-1})\)

- \(\mu \)
Viscosity \((\hbox {Pa}{\cdot } \hbox { s})\)

- \(\rho \)
Density \((\hbox {kg}{\cdot } \hbox {m}^{-3})\)

- \(\rho _{\mathrm{cu}}\)
Reflectivity of copper (–)

- \(\sigma \)
Stefan–Boltzmann constant \((\hbox {W}{\cdot } \hbox {m}^{-2}{\cdot } \hbox {K}^{-4})\)

- \(\tau _{\mathrm{D}}\)
Transmissivity of DSSC (–)

## Subscripts and Superscripts

- \(25\,{^{\circ }}\hbox {C}\)
Value at \(T_\mathrm{D} = 25\,{^{\circ }}\hbox {C}\)

- A
Ambient

- Cu
Copper

- D
DSSC

- i
Initial value

- in
Input value

- m
Melting point

- max
Maximum value

- oc
Open-circuit

- sc
Short-circuit

## Notes

### Acknowledgements

This work was supported by JSPS KAKENHI Grant Number 24560234. We thank T. Taguchi and Dr. T. Uchida (Associate Professor, Okayama University) for their contributions to these experiments.

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