Influences of Alq3 as electron extraction layer instead of Ca on the photo-stability of organic solar cells

Calcium (Ca) is not a desirable candidate as electron extraction layer (EEL) for long-term stability organic photovoltaics (OPVs) on account of its nature of active metal. In this paper, we has selected thieno[3,4-b]thiophene/benzodithiophene (PTB7) and [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) as donor and acceptor, respectively, and the device architecture is Glass/ITO/poly-(ethylenedioxythiophene):polystyrene sulphonate (PEDOT:PSS)/PTB7:PC71BM/EEL/Aluminum. For comparison, tris (8-hydroxyquinoline) aluminum (Alq(3)) and Ca were used as EEL to reveal their influence on the performance [power conversion efficiency (PCE), short-circuit current density (J(SC)), open-circuit voltage (V-OC) and fill factor (FF)] of the OPVs. As a result, PCE of the device with Ca as EEL rapidly reduced over 60% after three days due to the poor stability of Ca. The device with Alq(3) as EEL shows favorable stability owing to the PCE moderate declined less than 30% after one month. Furthermore, PCE of the device with Alq(3) as EEL was fully comparable to that with Ca as EEL. Our results indicate that Alq(3) is an alternative candidate for high-performance and long-term photo-stability OPVs. (C) 2013 Elsevier B.V. All rights reserved.