Abstract
High quality Mn2+-doped CdTe quantum dots (QDs), Co2+-doped CdTe QDs and Mn2+&Co2+ co-doped CdTe QDs were successfully synthesized via an aqueous phase method with mercaptopropanoic acid (MPA) ligands. The doped QDs maintain the same zinc blende structure of CdTe by X-ray diffraction (XRD). The Mn2+-doped CdTe QDs and Co2+-doped CdTe QDs both show a red-shift on absorption and photoluminescence (PL) spectra compared to pure CdTe QDs. In addition, Mn2+-doped CdTe QDs show a significant increase in the PL lifetime due to an orbitally forbidden d–d transition, which is of benefit to the reduction of electron recombination loss. Co2+ doping has a more matched doping energy level. In view of this, Mn2+&Co2+ co-doped CdTe QDs were applied as sensitizers for quantum dot sensitized solar cells, resulting in a significantly enhanced efficiency.
Highlights
IntroductionQuantum dots (QDs) have exhibited properties signi cantly different from their bulk materials.[1,2,3,4] The importance of these QDs is attributed to their unique properties such as band-gap tenability[2,3,4] and multiexciton generation (MEG).[5,6,7] Quantum dot sensitized solar cells (QDSCs)[8,9,10,11,12] have attracted much attention because of their promising development prospects in solar cells
CdTe has a narrower band gap (1.5 eV),[16] which expands the light absorption range to a longer wavelength, and has a higher conduction band edge makes the electrons injection from CdTe Quantum dots (QDs) to TiO2 photoanode faster.[17]
Take the supernatant and centrifugate at 8000 rpm for 5 min to obtain precipitation of the mercaptopropanoic acid (MPA) capped pure CdTe QDs, disperse with distilled water, labels CdTe-pure, to obtain Mn2+, Co2+ doped or co-doped in CdTe QDs, MnCl2, CoCl2 or both with Cd(NO3)[2] and MPA dissolved in distilled water [n(Mn) : n(Cd) 1⁄4 1 : 19, n(Co) : n(Cd) 1⁄4 1 : 19, n(Mn) : n(Co) : n(Cd) 1⁄4 1 : 1 : 18 and total cations remain 4 mmol], kept synthesize steps same, and label CdTe:Mn2+, CdTe:Co2+ and CdTe:Mn2+&Co2+, respectively
Summary
Quantum dots (QDs) have exhibited properties signi cantly different from their bulk materials.[1,2,3,4] The importance of these QDs is attributed to their unique properties such as band-gap tenability[2,3,4] and multiexciton generation (MEG).[5,6,7] Quantum dot sensitized solar cells (QDSCs)[8,9,10,11,12] have attracted much attention because of their promising development prospects in solar cells. The transition between 4T1–6A1 of Mn2+ is both spin and orbitally forbidden, as a result, the emission lifetime of Mn2+doped QDs measured to be in the range of milliseconds.[27] Long excited state lifetime is one of the key factors for the design and development of higher efficient QDSCs. In addition, the doping of transition metals could accelerate the electron transfer speed and reduce the electron recombination rate at the TiO2/electrolyte interface. Mn2+ doped QDs have applied in QDSCs with good performance.[27,28,29] On the other hand, doping a certain amount of cobalt could change energy level structure of semiconductor,[30] adjust the Fermi level of photoanode,[31] enhance light harvesting range,[32] and improve the performance of DSSCs. Considering the synergy of transition metals,[24,33] the different doping energy levels make it easier for electrons to transition. A systematic study was undertaken on the effects of doping on the recombination mechanism by optical absorption spectra, photoluminescence (PL) and PL decay spectra
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