Electron Trap to Electron Storage Center in Specially Aligned Mn-Doped CdSe d-Dot: A Step Forward in the Design of Higher Efficient Quantum-Dot Solar Cell

Abstract

Specially aligned surface-accumulated Mn-doped CdSe (MnCdSe) quantum dots (QDs) have been synthesized to study the effect of dopant atom on charge-carrier dynamics in QD materials. EPR studies suggest that the (4)T1 state of Mn(2+) lies above the conduction band of CdSe, and as a result no Mn-luminescence was observed from MnCdSe. Femtosecond transient absorption studies suggest that Mn atom introduces structural defects in surface-doped CdSe, which acts as electron trap center in doped QD for the photoexcited electron. Bromo-pyrogallol red (Br-PGR) were found to form strong charge-trasfer complex with both CdSe and MnCdSe QDs. Charge separation in both the CdSe/Br-PGR and MnCdSe/Br-PGR composites was found to take place in three different pathways by transferring the photoexcited hole of CdSe/MnCdSe QDs to Br-PGR, electron injection from photoexcited Br-PGR to the QDs, and direct electron transfer from the HOMO of Br-PGR to the conduction band of both the QDs. Hole-transfer dynamics are found to be quite similar (∼1.1 to 1.3 ps) for both of the systems and found to be independent of Mn doping. However, charge recombination dynamics was found to be much slower in the MnCdSe/Br-PGR system as compared with that in the CdSe/Br-PGR system, which confirms that the Mn dopant act as the electron storage center. As a consequence, the MnCdSe/Br-PGR system can be used as a better super sensitizer in quantum-dot-sensitized solar cell to increase efficiency further.

Effect of Molecular Coupling on Ultrafast Electron‐Transfer and Charge‐Recombination Dynamics in a Wide‐Gap ZnS Nanoaggregate Sensitized by Triphenyl Methane Dyes

“…The red‐shifted band in both PGR‐ and Br‐PGR‐sensitized ZnS NCs can be attributed to the formation of a CT complex between PGR/Br‐PGR and ZnS NCs. In our earlier investigation, we have observed the formation of CT complexes between CdSe and CdS quantum dots (QDs) and Br‐PGR molecules and ATC molecules. We have also carried out steady‐state absorption studies in the ATC/ZnS NC system.…”

“…In our previous investigation, we have demonstrated ultrafast interfacial electron‐transfer dynamics with a series of TPM dyes with different molecular structures and coupling . We have also reported CT dynamics with TPM‐dye‐sensitized CdSe and CdS QDs and found that a TPM‐dye–QD composite can act as a super‐sensitizer in a QD solar cell …”

Cascading electron and hole transfer dynamics in a CdS/CdTe core–shell sensitized with bromo-pyrogallol red (Br-PGR): slow charge recombination in type II regime

“…In addition to that lower QD loading on TiO 2 surface (as compared to dye loading in DSSC) resulting direct electron transfer from TiO 2 film to the oxidized redox couple in photo anode. However exciton dissociation through hole transfer is not widely reported in literature except few recent reports by us [26][27][28][29] and Kamat & co-workers 30 . Electron injection is much faster as compared to hole transfer, so for efficient devices hole has to extracted from QD surface as fast as possible 20 .…”

Luminescence, Plasmonic, and Magnetic Properties of Doped Semiconductor Nanocrystals

“…Fort he Mn-doped CdS/CdSe film the efficiency obtained was 5.42 %w hich was one of the highest for QDSSCs at the time of report. [40] In ar ecent development, Zhong and co-workers reported the best QDSSC based on aM n:CdSeTeQ Ds ensitizer and Mn:ZnS passivation with an efficiency of 9.4 %. [40] In ar ecent development, Zhong and co-workers reported the best QDSSC based on aM n:CdSeTeQ Ds ensitizer and Mn:ZnS passivation with an efficiency of 9.4 %.…”