CIPS/OSA Brown Bag Seminar Series

Thursday, December 6, 2007

12 noon , RLE Haus Conf. Room 36-428

"Planar Heterojunction Photovoltaics Consisting of a Printed Colloidal Quantum Dot Film and a Small Molecule Hole Transport Layer"

Alexi Arango

We begin with a brief overview of the product demands of the wildly expanding solar photovoltaics industry and introduce the potential advantages of molecular/nanoscale photovoltaics.   We describe how a planar heterojunction between cadmium selenide (CdSe) colloidal quantum dots (QDs) and a thermally evaporated N,N'-Bis(3-methylphenyl)-N,N'-bis-(phenyl)-9,9-spiro-bifluorene (spiro-TPD) transparent hole transport layer is achieved by printing the CdSe layer onto spiro-TPD with an elastomeric stamp.  In a photovoltaic structure, the planar interface facilitates charge separation and promotes directed charge diffusion toward the electrodes, resulting in a high open circuit voltage ( 1.3V) and a high built-in potential (1.5V).  We show that charge generated within the CdSe film is subject to transport losses due to the insulating QD capping ligands and, therefore, the internal quantum efficiency reaches a peak value of 30% at a film thickness of roughly three monolayers.