Ultrafast Hole- and Electron-Transfer Dynamics in CdS–Dibromofluorescein (DBF) Supersensitized Quantum Dot Solar Cell Materials

Abstract

Ultrafast charge-transfer (CT) dynamics has been demonstrated in CdS quantum dot (QD)−4′,5′-dibromofluorescein (DBF) composite materials, which form a strong CT complex in the ground state. Charge separation in the CdS−DBF composite was found to take place in three different pathways, by transferring the photoexcited hole of CdS to DBF, electron injection from photoexcited DBF to the CdS QD, and direct electron transfer from the HOMO of DBF to the conduction band of the CdS QD. CT dynamics was monitored by direct detection of the DBF cation radical and electron in the QD in the transient absorption spectra. Electron injection and the electron-transfer process are found to be pulsewidth-limited (<100 fs); however, the hole-transfer time was measured to be 800 fs. Charge recombination dynamics has been found to be very slow, confirming spatial charge separation in the CdS−DBF supersensitized quantum dot system. Grand charge separation process suggests that the CdS−DBF supersensitized quantum dot system can be used as superior materials for quantum dot solar cells (QDSCs).

Super Sensitization: Grand Charge (Hole/Electron) Separation in ATC Dye Sensitized CdSe, CdSe/ZnS Type‐I, and CdSe/CdTe Type‐II Core–Shell Quantum Dots

“…However, charge-transfer interactions between quantum dot materials and molecular adsorbates are not reported in literature except our recent report [28] on charge-transfer complex formation between di-bromo fluorescein (DBF) and CdS QD materials. ATC is one of the molecule in tri-phenyl methane series of dyes which have shown as potential sensitizer molecule in dye-sensitized solar cell (DSSC).…”

“…[17,18,[22][23][24] However, exciton dissociation in ultrafast time scale through hole transfer in QD/molecular adsorbates have not been reported in the literature. Hole-transfer time constants from photoexcited QD to molecular adsorbate are reported to be nanosecond to 100s of picoseconds time scale, [25][26][27] where no reports are available in the sub-picosec-ond time scale except some recent reports by us [28,29] and Kamat and co-workers. [21] We have reported hole-transfer times from photoexcited QD to molecular adsorbate of 800 fs and 500 fs in CdS/DBF system [28] and CdSe/PGR [29] system, respectively, as measured by femtosecond transient absorption spectroscopy.…”

“…Hole-transfer time constants from photoexcited QD to molecular adsorbate are reported to be nanosecond to 100s of picoseconds time scale, [25][26][27] where no reports are available in the sub-picosec-ond time scale except some recent reports by us [28,29] and Kamat and co-workers. [21] We have reported hole-transfer times from photoexcited QD to molecular adsorbate of 800 fs and 500 fs in CdS/DBF system [28] and CdSe/PGR [29] system, respectively, as measured by femtosecond transient absorption spectroscopy. Efforts have been made by many authors to improve efficiency of QDSC by using both type-I [30][31][32][33] and type-II [34][35][36] core-shell instead of single QD materials in which either core QD are protected from corrosion in type-I system or charge (electron or hole) transfer are facilitated in type-II system.…”

Передача электронного возбуждения из органической матрицы в нанокристаллы CdS, полученные методом Ленгмюра--Блоджетт

“…Органические материалы в совокупности с полупровод-никовыми НК перспективны для создания солнечных батарей [3][4][5][6]. В таких структурах ключевыми являются процессы передачи электронного возбуждения из орга-нической матрицы в НК [6][7][8][9][10][11].…”

“…Перенос электронного возбуждения из матрицы в НК активно исследовался для НК, находящих-ся в полупроводниковой матрице [12][13][14][15], а так-же для НК в проводящих органических соединени-ях poly [2-methoxy,5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) [5,9,16]. В последнем случае наблюда-ли как перенос электрона или дырки, так и экситона.…”