Organic:PbS-nanocrystal:Fullerene Hybrid Photovoltaics
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1102-LL07-06
Organic:PbS-nanocrystal:Fullerene Hybrid Photovoltaics Nanditha Dissanayake, Ross A Hatton, Cristina Giusca, Thierry Lutz, Richard Curry, and Ravi Silva Advanced Technology Institute, University of Surrey, Faculty of Engineering and Physical Sciences, Guildford, GU27XH, United Kingdom ABSTRACT Single and multi junction hybrid devices comprising oligoacenes, PbS quantum dots (PbS-QD) and C60 are demonstrated. A greatly improved performance of the PbS-QD /C60 system was obtained in this work. Furthermore, a study of using acenes (pentacene, tetracene) as light absorbers and photoinduced electron donors to PbS-QD was carried out. Fabricated devices were characterized under 1 Sun simulated solar irradiation and external quantum efficiency (EQE) measurements. The initial hybrid devices demonstrated up to 0.14 % power conversion efficiency under AM1.5G illumination and up to 16 % EQE at 400 nm. The single junction (PbSQD/C60) devices demonstrated greater than 1.2 % EQE at 1100 nm while multi junctional tetracene/PbS-QD/C60 devices exhibited up to 0.2 % EQE in the infrared region (1100 nm). Ultraviolet photoelectron spectroscopy was used to measure the molecular energy levels in the system under discussion to justify the photoinduced charge transfer. This work demonstrates new device systems which can be potentially be utilized to fabricate high efficient broad band absorbing hybrid photovoltaics. INTRODUCTION Hybrid devices with organic (polymer/small molecule) and inorganic nanocrystals (quantum dots/rods) have reported up to 1.7 % PCE. [1] Most of these hybrid devices utilize wide bandgap CdSe/CdTe based nanocrystals which are limited to absorbing only the high energy photons within the ultraviolet to the visible region. Recent work have reported hybrid devices fabricated with Pb chalcogenide nanocrystals having smaller band gaps tuned to absorb the infrared wavelengths which accounts for 1/3 of solar energy irradiated on the earth surface. [2-3] Previously we have demonstrated a hybrid bilayer discrete heterojunction photovoltaic device with PbS-QDs and C60 investigating the photoelectron donor nature of the PbS-QDs. [3] It was shown that the surfactant organic ligands (oleic acid) were detrimental to photoinduced charge injection in such devices and desorption of the ligands by thermal annealing increased the short circuit current (Jsc) by two orders of magnitude. In the present work we demonstrate an improved PbS-QD/C60 hybrid device which exhibit up to 0.14 % power conversion efficiency by using nanocrystals with shorter (butylamine) surfactant groups. Furthermore, mutijunction hybrid devices utilizing acenes (pentacene/tetracene), PbS-QD and C60 are fabricated to demonstrate broad band light absorption from the UV to near infrared wavelengths. Acenes
demonstrate the highest carrier mobility in organic semiconductors together with high absorption coefficients (105 cm-1) [4] Therefore, have been used to fabricate C60 based solar cells which demonstrated up to 2 % PCE. [5] A novel device structure is e
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