title: Colloidal quantum dot solar cells exploiting hierarchical structuring.
abstract: Extremely thin-absorber solar cells offer low materials utilization and simplified manufacture but require improved means to enhance photon absorption in the active layer. Here, we report enhanced-absorption colloidal quantum dot (CQD) solar cells that feature transfer-stamped solution-processed pyramid-shaped electrodes employed in a hierarchically structured device. The pyramids increase, by up to a factor of 2, the external quantum efficiency of the device at absorption-limited wavelengths near the absorber band edge. We show that absorption enhancement can be optimized with increased pyramid angle with an appreciable net improvement in power conversion efficiency, that is, with the gain in current associated with improved absorption and extraction overcoming the smaller fractional decrease in open-circuit voltage associated with increased junction area. We show that the hierarchical combination of micron-scale structured electrodes with nanoscale films provides for an optimized enhancement at absorption-limited wavelengths. We fabricate 54.7° pyramid-patterned electrodes, conformally apply the quantum dot films, and report pyramid CQD solar cells that exhibit a 24% improvement in overall short-circuit current density with champion devices providing a power conversion efficiency of 9.2%.
authors.affiliation: Department of Electrical and Computer Engineering, University of Toronto , 10 King's College Road, Toronto, Ontario M5S 3G4, Canada.
authors.forename: André J
authors.initials: AJ
authors.lastname: Labelle
authors.forename: Susanna M
authors.initials: SM
authors.lastname: Thon
authors.forename: Silvia
authors.initials: S
authors.lastname: Masala
authors.forename: Michael M
authors.initials: MM
authors.lastname: Adachi
authors.forename: Haopeng
authors.initials: H
authors.lastname: Dong
authors.forename: Maryam
authors.initials: M
authors.lastname: Farahani
authors.forename: Alexander H
authors.initials: AH
authors.lastname: Ip
authors.forename: Andrea
authors.initials: A
authors.lastname: Fratalocchi
authors.forename: Edward H
authors.initials: EH
authors.lastname: Sargent
keywords: Colloidal quantum dots; photonically enhanced solar cells; photovoltaics; structured substrates