Chemically deposited n-CdSe thin film photo-electrochemical cells: effects of Zn2+-modification

Abstract

The photoelectrochemical solar cell properties of chemically deposited n-CdSe films were studied before and after Zn 2+ surface modification. It was shown that the surface properties underwent conceivable changes after Zn 2+ treatment. The current-voltage characteristics in the dark showed a significant decrease in reverse saturation current density, Jo, from 5.4 x 10 -7 to 1.2 x 10 _9 Acm -2 and in ideality factor, n, from 2.46 to 1.27. Under AM1 illumination, other parameters have been found to be considerably enchanced, e.g. the open-circuit photovoltage, Voc, increased from 0.53 to 0.85 V with respect to SCE; the short-circuit photocurrent density, Jso, from 2.62 to 8.35 mAcm-2; fill factor from 0.38 to 0.62 and the minority carrier diffusion length, Lp, from 0.16 to 0.22 #m. X-ray photoelectron spectroscopic data on the Zn2+-modified CdSe showed the formation of metallic Zn islets and a thin layer of Se02 on the surface. All these important improvements of the CdSe PEC properties may be attributed to the redistribution of active interface states within the band gap due to strong interaction of the electrodepositive Zn 2+ ions. Support for these observations were obtained by sub-band gap response studies, contact potential difference measurements in N 2 ambient and the estimation of the surface recombination velocities before and after modification.

Morphology and band gap controlled AACVD of CdSe and CdS Se1− thin films using novel single source precursors: Bis(diethyldithio/diselenocarbamato)cadmium(II)

“…Bis(n-hexy (methyl)dithio/selenocarbamato)cadmium/zinc proved to be the best of the unsymmetrical derivatives for the growth of chalogenides [18][19][20][21][22] caused by undesirable ligand degradation reactions. Other methods used to deposit CdSe thin films include vacuum evaporation and co-evoparation [30] molecular beam deposition [31], laser ablation [32], electrochemical deposition [33][34][35], spray pyrolysis [36][37][38], and chemical bath deposition [3,[38][39][40][41][42][43][44]. A convenient and controllable hydrothermal synthetic method based on a reaction in an aqueous system to produce CdSe nanostructures of different sizes and shapes was reported [44].…”

Morphology and photoelectrochemical behaviour of CdSe/ZnO composites obtained by the screen printing technique

“…Surface modification by ZnCl 2 treatments was reported to increase the quantum efficiencies. The growth of a thin SeO 2 layer was thought to be responsible for the muchimproved film stability, while the increase in band bending and shift in Fermi level were reported to be due to additional surface charges provided by the Zn 2+ ions [6]. Earlier reports on ZnCl 2 surface modification [1,[7][8][9], that indicated that this treatment causes a decrease in dark current, are consistent § Author to whom correspondence may be addressed.…”

“…While the results of ZnCl 2 surface modification reported an increase in both short circuit current and stability [6], the improvement in photocurrent has usually been correlated to a decrease in long term stability. That was the case in CdSe films coated with a thin film (350 Å) of ZnO [10] where the improvement in stability was obtained at the expense of cell performance.…”

“…The method of preparation requires the semiconductor powder to be mixed with a fluxing material (e.g., ZnCl 2 ), and dispersed in liquid to obtain a paste or slurry. The choice of ZnCl 2 as the flux might have additional advantages and benefit from the mechanisms described for Zn 2+ surface modification of photoelectrodes [6]. Surface modification by ZnCl 2 treatments was reported to increase the quantum efficiencies.…”

CdS<sub>x</sub>Se<sub>y</sub>/TiO<sub>2</sub> Solar Cell Prepared with Sintered Mixture Deposition

“…Efficient electron injection from the photoexcited QD into the TiO 2 conduction band requires close QD-TiO 2 contact. Deposition of CdSe-QD layers on a conducting transparent substrate (usually fluorine doped tin oxide-FTO) covered with nano-crystalline(NC)-TiO 2 by using simple dipping has been reported to be applicable (direct absorption-DA) [19][20][21][22][23]. Anchoring QDs on TiO 2 by linker molecules containing both carboxylate and thiol functional groups is another approach to achieve close and stable contact (linker technique) [12,21,24].…”