Preparation Of CuInSe₂ And TiO₂ Semiconductor Films By Solution Process And Properties Of Their Heterogeneous Structure

The NPC solar cell is a very promising kind of solar cells as it is cheap, easy to manufacture and high air stability. Here TiO₂ was used as photo-anode, and CuInSe₂ as inorganic sensitizer. CuInSe₂ films were prepared both by successive ionic layers adsorption and reaction (SILAR) method and electrodeposition method on glass substrate, and TiO₂ films were prepared by Sol-Gel method. Subsequently, the CuInSe₂ films were electrodeposited on TiO₂ films to form TiO₂/CuInSe₂ heterogeneous structure.In the CuInSe₂ preparation by SILAR method, triethanolamine and sodium citrate were used to complex Cu²⁺ and In³⁺, respectively, to form the Cu and In mixed cationic precursor solutions. The results indicitated that the Cu and In mixed cationic precursor solutions resulted in more uniform distribution for Cu, In and Se elements than the separated cationic precursors. The temperature elevation of precursor solutions could accelerate the growth of CuInSe₂ films. Chalcopyrite CuInSe₂ thin film with near stoichiometry was obtained from Cu/In mol ratio =1.5 in mixed cationic precursor solution after annealed at 400℃for 30min. The suitable rise of annealing temperature and time is beneficial for improvement of CuInSe₂ crystallization.In the process of CuInSe₂ electrodeposition, sodium citrate were used to complex Cu, In and Se elements in order to tune the pH value to 6⁷. In this mild solution conditions, the deposition potentials for Cu, In, and Se elements had a big difference with each other, and Se element required the most negative potential to be deposited. Thus, one step electrodepostion with an alternating double-potentiostatic (DPSED) program was used to prepare CuInSe₂ thin films in the nearly neutral aqueous electrolytes, and the double potential parameters were V1=-800mV and V2=-1400mV. The step time had influences on the morphology and components of CuInSe₂ films, and the appropriate time were t1=30s and t2=60s. When the Cu/In/Se mol ratio was 2/0.4/4⁵ in the electrolytes, the deposited CuInSe₂ films were near to Cu: In: Se = 1:1:2 stoichiometry, and the band gap is 1.05eV.In TiO₂ Sol-Gel preparation, acetaldoxime (CH₃CH=NOH) was used as a new ligand, and F127 and Brij56 were used as pore-forming agent. The organic parts were decomposed at 350⁴00℃. The results showed that the TiO₂ prepared by CH₃CH=NOH-modified Ti(OiPr)4 could preserve high BET surface, small particle size and narrow pore distribution even at higher calcinating temperature. The highest BET surface is 219m²/g for TiO₂ sample with F127 and 283m²/g for sample with Brij56, respectively, after calcinated at 350℃.For the CuInSe₂ electrodeposition on TiO₂ substrate, the deposition potentials had nearly 200mV negative shift compared with the deposition potentials on ITO substrate. Thus the best deposition parameters were changed to V1=-1000mV, t1=30s, V2=-1600mV, t2=60s, under which the prepared CuInSe₂ films were near 1:1:2 stoichiometry. After 6 cycles, the thickness of prepared CuInSe₂ films was about 300nm. The heterogeneous solar cell was designed as ITO/TiO₂/CuInSe₂/electrolyte/Pt structure. The biggest open-circuit voltage was 446mV, and the biggest short-circuit current was 0.0054 mA/cm².