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CdSeTe/CdS Type-I Core/Shell Quantum Dot Sensitized Solar Cells with Efficiency over 9%

Yang, Junwei, Wang, Jin, Zhao, Ke, Izuishi, Takuya, Li, Yan, Shen, Qing, Zhong, Xinhua
The Journal of Physical Chemistry C 2015 v.119 no.52 pp. 28800-28808
absorption, coatings, dielectric spectroscopy, electric power, lighting, models, photovoltaic cells, quantum dots, silica
Surface trap defects are the limited factor for quantum dots (QDs) application in solar cells. The trapping states can be efficiently suppressed by coating a shell of wider band gap material around the core QDs. We choose CdSe₀.₆₅Te₀.₃₅ (simplified as CdSeTe) as a model core material, and CdS shell was then overcoated around the CdSeTe core QD to decrease surface defect density and to increase the stability of the core QDs. By optimizing the thickness of the CdS shell, the power conversion efficiency (PCE) of the CdSeTe/CdS quantum dots sensitized solar cells (QDSCs) is enhanced by 13% in comparison with that of plain CdSeTe QDSCs. Transient absorption (TA), incident-photo-to-carrier conversion efficiency (IPCE), open-circuit voltage decay (OVCD), and electrochemical impedance spectroscopy (EIS) measurements confirmed the suppressed charge recombination process in internal QDs and QD/TiO₂/electrolyte interfaces with the overcoating of CdS shell around CdSeTe core QDs. With the further overcoating of a-TiO₂ and SiO₂ barrier layers around the QD-sensitized photoanode, the PCE of champion CdSeTe QDSCs achieved 9.48% (Jₛc = 20.82 mA/cm², Vₒc = 0.713 V, FF = 0.639) with average PCE 9.39 ± 0.09% under AM 1.5 G one full sun illumination.