Electrodeposited ZnO/Cu2O heterojunction solar cells

Identification of Copper(II)–Lactate Complexes in Cu2O Electrodeposition Baths: Deprotonation of the α-Hydroxyl Group in Highly Concentrated Alkaline Solution

“…An equivalence point is observed when the NaOH concentration (c NaOH = c HL + 0.75c Cu(II) ) was approximately 3.3 M, indicating that OH -reacted further with complexed copper(II) species in a Cu(II):OH -molar ratio of about 1:0.75, which appears to be the same value as that observed by Leopold et al 18 The pH at the equivalence point was 10.4; however, the pH following each drop of titrant was found to be unstable, and was observed to decrease during the waiting time, which indicates 2 18.81 24 that the reaction had not reached chemical equilibrium on the titration timescale by traditional burette infusion. Therefore, we performed "revised pH titration" to ensure sufficient reaction time.…”

“…Here, it is reasonable to consider that 2 2-, and/or Cu(H -1 L) 2 L 3-are formed from the CuL 2 and/or CuL 3 -complexes under alkaline conditions as follows: …”

“…We obtained clear mass spectra that revealed the dissolved species. We conclude that the unknown copper(II)-lactate complexes are Cu(H -1 L)L -and Cu(H -1 L) 2 2-(see Figure 1). As far as we know, this is the first direct experimental observation of H -1 L 2-ions coordinated to copper(II) ions.…”

“…6,15,16 Unfortunately, to the best of our knowledge, there are no available thermodynamic data for these copper(II)-lactate complexes under these alkaline conditions, especially for such concentrated solutions. Two previous reports have indicated the presence of dissolved copper(II)-lactate complexes in such concentrated alkaline solutions; Leopold et al assumed that the copper(II)-lactate complexes are Cu(H -1 L) 2 2-and Cu(H -1 L) 2 (OH) 3-(H -1 L 2-= CH 3 CH(O -)COO -, the lactate ion bearing a deprotonated α-hydroxyl group) based on a pH-titration experiment at pH > 8, and by analogy with the alkaline copper(II)-tartrate system, 18 while Achilli et al proposed CuL 4 2-on the basis of energy-dispersive X-ray absorption spectroscopy (EDXAS), where they assumed that L -functions unusually as a monodentate ligand. 19 These different results leave the copper(II)-lactate complexes in these Cu 2 O-electrodeposition baths open to question; consequently, other direct information is required.…”

“…Cu 2 O thin films are attracting increasing attention as solar-cell materials, [1][2][3][4][5] photocathodes, [6][7][8][9] and photocatalysts [10][11][12] for, for example, water splitting. Among thin-film fabrication methods, electrodeposition from an aqueous solution has advantages over conventional methods, such as chemical vapor deposition, because of its low cost and low environmental burden.…”