Structurally Driven Ultrafast Charge Funneling in Organic Bulk Heterojunction Hole Transport Layer for Efficient Colloidal Quantum Dot Photovoltaics

摘要

Nanoscopic packing structures crucially determine the charge conductionand the consequent functionalities of organic semiconductors includingbulk heterojunctions (BHJs), which are dependent on various processingparameters. Today’s high-performance colloidal quantum dot photovoltaics(CQDPVs) employ functional organic semiconductors as a hole transportlayer (HTL). However, the processing of those films replicates a protocol dedicatedto high-performance organic PVs, and thus little is known about howto control the molecular packing structures to maximize the hole extractionfunction of the HTLs. Herein, it is uncovered that the random-oriented, butcloser-packed BHJ crystallites, constructed by 1,2-dichlorobenzene (o-DCB)as a solvent, allow exceptional charge conduction vertically across the filmand restrict diffusion-driven charge transfer process, enabling ultrafast holefunneling from CQD to BHJ to be extracted. As a result, a power conversionefficiency of 13.66% with high photocurrent >34 mA cm~(?2) is achieved byemploying o-DCB-processed BHJ HTL, far exceeding the performance of theCQDPV solely employing neat polymer HTL. A charge conduction mechanismassociated with the BHJ HTL structure suppressing the bimolecularrecombination is proposed. This works not only suggests key principles tocontrol the packing structures of organic HTLs but also opens a new avenueto boost optoelectronic performance.