A discovery from the materials laboratory at Universitas Indonesia has opened a new perspective on affordable and environmentally friendly solar cells. Dr. drg. Bambang Priyono, S.U., together with his research team from the Department of Metallurgical and Materials Engineering, Universitas Indonesia, successfully demonstrated that titanium dioxide (TiO₂) nanoparticles synthesised through a sol-gel process and treated with hydrothermal methods could function as an active component in dye-sensitized solar cells (DSSCs)—a type of solar cell that uses dye molecules as light absorbers. Published in the 2018 edition of IOP Conference Series: Materials Science and Engineering, this research addressed a fundamental question: at what hydrothermal treatment temperature can the best performance be achieved?
Solar Cells Are No Longer Limited to Expensive Panels
DSSC technology is not new, but it offers advantages that conventional solar panels have yet to fully achieve: lower production costs, relatively simple manufacturing processes, and a cleaner environmental footprint. Unlike silicon-based solar cells, which require high-temperature processing and expensive raw materials, DSSCs operate based on a mechanism inspired by photosynthesis. Light is absorbed by dye molecules, and the energy is then transferred to a porous oxide semiconductor layer—typically TiO₂—before eventually being converted into electrical current.
The key lies in the TiO₂ layer itself. The larger its surface area, the more dye molecules can attach to it. The higher the crystallinity of the material, the more efficiently electron transfer can occur. However, these two characteristics—surface area and crystallinity—often compete with each other. Improving one may compromise the other. This balance was the challenge that Dr. drg. Bambang Priyono, S.U., and his team attempted to solve.
From Gel to Crystal: The Journey of Nanoparticles
The research team synthesised TiO₂ using the sol-gel method, beginning with titanium tetra-n-butoxide as the raw material, which was dissolved in ethanol and hydrochloric acid, followed by gradual addition of water. The mixture was stirred for three hours and then allowed to dry into a xerogel. It was subsequently subjected to three stages of calcination: 150°C to evaporate solvents; 300°C to remove remaining organic compounds; 420°C to form the anatase phase of TiO₂, the crystal phase known for its high photoelectrochemical activity.
After calcination, the TiO₂ powder underwent post-hydrothermal treatment in a Teflon-lined autoclave at three different temperatures: 100°C; 120°C; 150°C; for 14 hours. This process was designed to improve the Ti-O-Ti bonding network, creating a more organised crystal structure without significantly reducing surface area.
As a comparison, the researchers also used commercial P-25 Degussa TiO₂, an industrial standard material known for its high crystallinity.
The Numbers Speak: 120°C Takes the Lead
Characterisation using X-ray diffraction (XRD), BET surface area measurements, and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) revealed interesting results. The sample treated at 150°C produced the largest crystal size, measuring 10.55 nm, with a surface area of 95.38 m²/g and a band gap energy of 3.36 eV.
Meanwhile, the 100°C sample had the highest surface area at 117.96 m²/g, although its crystal size was only 5.49 nm. However, when all samples were assembled into DSSC prototypes and tested using a 50-watt projector lamp, the results were unexpected. The sample treated at 120°C produced the highest open-circuit voltage (V_OC) of 250 mV. The 150°C sample followed with 244 mV, while the 100°C sample produced 142 mV. The most surprising result came from commercial P-25 Degussa TiO₂, the industrial benchmark with the highest crystallinity, which generated only 31.2 mV due to its extremely low surface area of only 13.64 m²/g.
“The post-hydrothermal process has made the stiff Ti-OH network become more flexible and rearranged into Ti-O-Ti after completion of the hydrolysis process. Ti-O-Ti rearrangement has helped increase the crystallinity of TiO₂ and enabled the sample to achieve better performance.” — B. Priyono et al., IOP Conference Series: Materials Science and Engineering, 2018
These findings demonstrate that DSSC performance is not determined by a single factor. Instead, crystallinity, surface area, and band gap energy must work together. The 120°C sample achieved the most balanced combination: Crystal size: 8.85 nm, Surface area: 92.25 m²/g, and Sufficiently low band gap energy to maximise photon absorption.
Relevance Beyond the Laboratory
This research is not merely an exploration of materials. Amid Indonesia’s growing need for affordable renewable energy sources, the development of DSSCs based on locally synthesised TiO₂ opens realistic possibilities. The sol-gel method does not require large-scale industrial equipment. The raw materials are relatively accessible, and the hydrothermal process can be controlled simply by adjusting oven temperature.
More importantly, this research demonstrates that processing parameters can be systematically optimised. The 120°C temperature is not a magical number—it is the balance point discovered through controlled experimentation. The next steps involve measuring full power conversion efficiency and testing the long-term durability of the prototypes. These two factors will determine whether this technology can move beyond laboratory benches and become practical for applications such as residential solar systems.
Authors: Achmad Zam Zam Aghasy, DDS, M.Kes.; Hazra Alifia Muharam
Photo: Freepik
Source DOI: https://doi.org/10.1088/1755-1315/105/1/012121