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Suppressing Interfacial Dipoles to Minimize Open‐Circuit Voltage Loss in Quantum Dot Photovoltaics
Author(s) -
Lim Hunhee,
Kim Donghun,
Choi MinJae,
Sargent Edward H.,
Jung Yeon Sik,
Kim Jin Young
Publication year - 2019
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201901938
Subject(s) - materials science , pedot:pss , bilayer , schottky barrier , optoelectronics , homo/lumo , organic solar cell , open circuit voltage , quantum dot , band gap , photovoltaics , energy conversion efficiency , polystyrene sulfonate , dipole , active layer , nanotechnology , photovoltaic system , layer (electronics) , voltage , electrical engineering , chemistry , polymer , biochemistry , thin film transistor , organic chemistry , engineering , diode , membrane , molecule , composite material
Quantum‐dot (QD) photovoltaics (PVs) offer promise as energy‐conversion devices; however, their open‐circuit‐voltage ( V OC ) deficit is excessively large. Previous work has identified factors related to the QD active layer that contribute to V OC loss, including sub‐bandgap trap states and polydispersity in QD films. This work focuses instead on layer interfaces, and reveals a critical source of V OC loss: electron leakage at the QD/hole‐transport layer (HTL) interface. Although large‐bandgap organic materials in HTL are potentially suited to minimizing leakage current, dipoles that form at an organic/metal interface impede control over optimal band alignments. To overcome the challenge, a bilayer HTL configuration, which consists of semiconducting alpha‐sexithiophene (α‐6T) and metallic poly(3,4‐ethylenedioxythiphene) polystyrene sulfonate (PEDOT:PSS), is introduced. The introduction of the PEDOT:PSS layer between α‐6T and Au electrode suppresses the formation of undesired interfacial dipoles and a Schottky barrier for holes, and the bilayer HTL provides a high electron barrier of 1.35 eV. Using bilayer HTLs enhances the V OC by 74 mV without compromising the J SC compared to conventional MoO 3 control devices, leading to a best power conversion efficiency of 9.2% (>40% improvement relative to relevant controls). Wider applicability of the bilayer strategy is demonstrated by a similar structure based on shallow lowest‐unoccupied‐molecular‐orbital (LUMO) levels.