Influence of 4-guanidinobutyric acid as coadsorbent in reducing recombination in dye-sensitized solar cells

Dye-sensitized solar cells based on nanocrystalline TiO₂ have been fabricated with an amphiphilic ruthenium sensitizer [Ru (4,4′-dicarboxylic acid-2,2′-bipyridine) (4,4′-bis(p- hexyloxystyryl)-2,2′-bipyridine)(NCS)₂], coded as K-19, and 4-guanidinobutyric acid (GBA) as coadsorbent. The cells showed a ∼50 mV increase in open-circuit voltage and a similar current in comparison with cells without GBA cografting. The performance of both types of devices was evaluated on the basis of their photocurrent-voltage characteristics, dark current measurements, cyclic voltammetry, electrochemical impedance spectroscopy, and phototransient decay methods. The results indicate that GBA shifted the conduction band of TiO₂ toward a more negative potential and reduced the interfacial charge-transfer reaction from conduction band electrons to triiodide in the electrolyte (also known as the back reaction). In addition, the devices with GBA cografting showed an excellent stability with a power conversion efficiency of approximately 8% under simulated full sunlight (air mass 1.5, 100 mW cm^-2) during visible light soaking at 60°C.