Ultrafast Dynamics Group
Frédéric Laquai's Group

Molecular Doping

Molecular Doping of the Hole-Transporting Layer for Efficient, Single-Step-Deposited Colloidal Quantum Dot Photovoltaics

Molecular Doping of the Hole-Transporting Layer for Efficient, Single-Step-Deposited Colloidal Quantum Dot Photovoltaics 

A.R. Kirmani, F.P. Garcia De Arquer, J.Z. Fan, J.I. Khan, G. Walters, S. Hoogland, N. Wehbe, M.M. Said, S. Barlow, F. Laquai,
E.H. Sargent, A. Amassian. ACS Energy Lett. 2017, 2 (9), 1952-1959, DOI: 10.1021/acsenergylett.7b00540
A.R. Kirmani, F.P. Garcia De Arquer, J.Z. Fan, J.I. Khan, G. Walters, S. Hoogland, N. Wehbe, M.M. Said, S. Barlow, F. Laquai, E.H. Sargent, A. Amassian
Molecular Doping, Quantum Dot Photovoltaics
2017
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 Employment of thin perovskite shells and metal halides as surface-passivants for colloidal quantum dots (CQDs) has been an important, recent development in CQD optoelectronics. These have opened the route to single-step-deposited high-performing CQD solar cells. These promising architectures employ a CQD hole-transporting layer (HTL) whose intrinsically shallow Fermi level (EF) restricts band-bending at maximum power-point during solar cell operation limiting charge collection. Here, we demonstrate a generalized approach to effectively balance band-edge energy levels of the main CQD absorber and charge-transport layer for these high-performance solar cells. Briefly soaking the CQD HTL in a solution of the metal–organic p-dopant, molybdenum tris(1-(trifluoroacetyl)-2-(trifluoromethyl)ethane-1,2-dithiolene), effectively deepens its Fermi level, resulting in enhanced band bending at the HTL:absorber junction. This blocks the back-flow of photogenerated electrons, leading to enhanced photocurrent and fill factor compared to those of undoped devices. We demonstrate 9.0% perovskite-shelled and 9.5% metal-halide-passivated CQD solar cells, both achieving ca. 10% relative enhancements over undoped baselines.