KAJIAN SIFAT OPTIK DAN ELEKTRONIK KLOROFIL ALAM SEBAGAI MATERIAL AKTIF FOTOSENSITIZER ORGANIK; STUDY ON OPTICAL AND ELECTRICAL PROPERTIES OF NATURAL CHLOROPHYLL AS THE ACTIVE MATERIAL OF ORGANIC PHOTOSENSITIZER

Agus Supriyanto, S.S.i, M.Si, Kusminarto

2011 | Tesis | PROGRAM STUDI S3 ILMU FISIKA

Semiconducting materials based on organic natural products has been widely developed, produced and applied in the microelectronics and optoelectronics devices. Application of organic compound of phorphyrin and its metal complexes as photodetector and solar cell has been investigated. Research on natural chlorophyll that is available in the nature as a sensitizer for photodetector is still limited and needs to be well developed. Isolation of natural chlorophyll from a variety of natural resources such as mengkudu, cassava, spinach, microalgae clorella, and microalgae spirulina has been carried out using extraction and chromatography techniques. The cholorophyll solution was characterized using UV-Vis spectroscopy, FTIR spectroscopy, and current-voltage (I-V) to determine its photoconductivity. Microalgae spirulina has better chlorophyll content and is relatively easy to isolate. The UV-Vis spectrum of chlorophyll has soret band at 410 nm and Q band at 660 nm, consistent with that of typical chlorophyll. Its dark conductivity is about 1.07x10-5 ohm-1.cm-1 and when it is irradiated with intensity of 100 mW/cm2 becomes 1.54 x10-5 ohm-1.cm-1. The growth of chlorophyll film was realized by spin coating technique. The concentration of chlorophyll solution, spin rate and spin time, temperature, and time of heating are optimized first. The best conditions are attained where concentration of chlorophyll at 5.67 ?g/mL, spin rate at 1500 rpm, time of spin 60 seconds, and heating temperature below 200oC for 15 minutes. The chlorophyll thin film has HOMO-LUMO band gap of 2.15 eV and it is consistent with the results of semi-empirical calculation using ZINDO/S method. The conductivity of chlorophyll thin films increases with incerase in heating temperature for both ohmic and SCLC conditions. For ohmic condition at 373 K, conductivity of the film is 1.2x10-13 ohm-1.cm-1 and for SCLC condition is 1.48x10-12 ohm-1.cm-1. The activation energies at various applied potential for ohmic condition from 0.1-0.8 volts was found to be 0.16 – 0.19 eV. In the fabrication of devices based on organic photodetectors, the chlorophyll was combined alternatively with inorganic semiconductor of TiO2 nanoparticle. The first device configuration is ITO/TiO2/chlorophyll/Al and the second one is ITO/chlorophyll/TiO2/Al. For both devices, chlorophyll film was made with 1, 3, 5 and 7 times of spin coating. The best photovoltaic effect is obtained from device made by 3 times of spin coating. The device ITO/chlorophyll/TiO2/Al obtained with 3 times spin coating of chlorophyll shows the highest Jsc of 5.76 ?A/cm-2, Voc of 648 mV and responsivity 5.75x10-5 A/W. This work shows that natural chlorophyll isolated from microalgae spirulina has good sensitizing effect and it can be applied as organic photodetector. These research outputs are potential to be developed in the design of solar cell to help ease energy future shortage.

Kata Kunci : Natural chlorophyll, TiO2, Photosensitizing, Photodetector, Solar cell