© 2015 American Chemical Society. Colloidal quantum dots (CQD) are an attractive thin-film material for photovoltaic applications due to low material costs, ease of fabrication, and size-tunable band gap. Unfortunately, today they suffer from a compromise between light absorption and photocarrier extraction, a fact that currently prevents the complete harvest of incoming above-band-gap solar photons. We have investigated the use of structured substrates and/or electrodes to increase the effective light path through the active material and found that these designs require highly conformal application of the light-absorbing films to achieve the greatest enhancement. This conformality requirement derives from the need for maximal absorption enhancement combined with shortest-distance charge transport. Here we report on a means of processing highly conformal layer-by-layer deposited CQD absorber films onto microstructured, light-recycling electrodes. Specifically, we engineer surface hydrophilicity to achieve conformal deposition of upper layers atop underlying ones. We show that only with the application of conformal coating can we achieve optimal quantum efficiency and enhanced power conversion efficiency in structured-electrode CQD cells.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): KUS-11-009-21
Acknowledgements: This publication is based in part on work supported by Award KUS-11-009-21, made by King Abdullah University of Science and Technology (KAUST), by the Ontario Research Fund Research Excellence Program, and by the Natural Sciences and Engineering Research Council (NSERC) of Canada. The authors thank Larissa Levina for assistance in the CQD synthesis, Oleksandr Voznyy for assistance with SCAPS modeling software, and Elenita Palmiano, Remi Wolowiec, Ghada Koleilat, Silvia Masala, Haopeng Dong, and Damir Kopilovic for their technical help over the course of this study. A.J.L, S.M.T., and E.H.S. designed the study. A.J.L. prepared and characterized (AM1.5, absorption, EQE) all samples and analyzed all data, with assistance from K.W.K. A.J.L. and J.Y.K. performed contact angle measurements. A.J.L. performed FDTD and SCAPS simulations, while D.Z. performed Sentaurus optoelectronic device simulations. A.J.L. and X.L. developed and optimized procedures for dip-coating CQD devices. A.J.L. wrote the manuscript with feedback from S.M.T. and E.H.S.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.