Palestinian Conference on Graduate Students Research in Natural and Applied Sciences, At Birzeit University, Birzeit, Palestine

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Research Title: 
Modifying PEC characteristics of CuS thin film electrodes prepared by electrodeposition: Effect of cooling rate and coverage with electroactive composite materials
Rana Sultan Al-Kerm, Ahed Zyoud, Hikmat S. Hilal
Rana Sultan Al-Kerm, Ahed Zyoud, Hikmat S. Hilal
Sun, 2013-12-22
Research Abstract: 
CuS thin films have been grown on FTO/glass substrates by electrodeposition in acidic solution for photoelectrochemical conversion (PEC) of light into electricity. Different parameters have been investigated for this purpose: deposition time (7.5, 15 and 30 min), annealing the prepared films at different temperatures (150, 250 and 350oC) under nitrogen for 1 hr, and cooling rate. The annealed films were cooled to room temperature using two methods either slow or fast cooling. Moreover, tetra (-4-pyridyl porphyrinatomanganese) (ΙΙΙ) sulfate complex (MnP) embedded inside commercial Poly Ethylene (PE) polymer matrix was used to cover the prepared CuS films.
Effects of annealing temperature, cooling rate, deposition time, and covering with MnP-PE matrix on the film characteristics were studied for different films by AFM, PL spectra, electronic absorption spectra, dark J-V plots, photo J-V plots efficiency enhancement, value of short-circuit current and stability under PEC condition.
Different electrolytic solutions were used to find the best system with highest efficiency. Effect of annealing time (1, 2 and 3 hrs) on the efficiency of the prepared thin films, annealed at 250oC was studied after covering them with MnP-PE matrix.
CuS thin film is unstable under air atmosphere it is readily oxidized to CuO, CuSO4. Annealing CuS enhanced its stability by protect the film from oxidation, but annealing alone failed to protect the film from photo corrosion, so it still didn’t show any PEC results. Covering the annealed films with electroactive materials MnP in PE matrix enhanced efficiency and stability the film under PEC conditions. 
AFM, electronic absorption spectra, photo J-V plots showed the 15 min deposition time films have more uniform, smoother, more homogeneous surfaces, stronger electronic absorption with higher conversion efficiency and fill factor (15.23% and 78.195% respectively) than other counterparts.
The 250oC annealing temperature followed by fast cooling was found to be the best annealing temperature, since it gave higher conversion efficiency and fill factor, more homogeneous surfaces, better stability than other counterparts.
Covering the pre-annealed CuS thin films enhance PL & electronic absorption spectra, photo J-V plots, percentage conversion efficiency, fill factor and stability. Moreover pre-annealing for 2 hrs and covering the CuS films with MnP-PE matrix gave highest conversion efficiency and fill factor (17.3%, 85.6% respectively).
Two different organic redox couples were used in the PEC measurement (I2/KI & Fe (CP)2 /Fe(CP)2PF6 ). The Fe (CP)2 /Fe(CP)2PF6 system gave higher percentage conversion efficiency and fill factor than other counterpart.
Different aqueous electrolytic solutions FeCl2/FeCl3, NaOH/S-2/Sx-2, K3Fe (CN)6/K4Fe(CN)6/ LiClO4, I2/KI on PEC characteristics of pre-annealed covered CuS thin film electrodes have been studied, FeCl2/FeCl3 gave higher percentage conversion efficiency and fill factor than other counterparts.

Based on this study, it is strongly recommended to pre-anneal CuS films and cover them with MnP/PE matrices before using them in PEC processes.