Fabrication and Characterization of Inverted Type Organic Solar Cells with Nano-structure

Abstract

The aim of this study is to fabricate high-efficient inverted-type organic solar cells (OSCs) using the solution-based spin-coating method which is a simple and cost-saving method to coat each layer in the OSC The strategy to increase the power conversion efficiency (PCE) is to build structures in micro- or nanometer scale on the layers of the OSC The overall experiment will be discussed as follows: 1 The ZnO film is served as the electron transport layer in the inverted-type OSC The ZnO film was produced with the sol-gel method followed by annealing and further characterized with SEM EDS XRD and XPS Finally the PCE and lifetimes of the OSCs with the inverted type and the normal type were compared The PCE of the inverted-type OSC reached 2 58% which is comparable to that of the normal-type OSC The lifetime of the inverted-type OSC was prolonged to over a month while the normal structure OSC only maintained for half-day 2 The nanostructure was imprinted on the ZnO layer and the active layer in OSC to enhance the fill factor (FF) by increasing the contact area between the two layers The incident light would be scattered by the nanostructure which increases the light trapping ability and the short-circuit current density (Jsc) The resulting PCE increased from 2 46% to 3 0% 3 Unlike the bulk-heterojunction (BHJ) structure used to fabricate the blended active layer the active layer of the designed OSCs was built into a bilayer-like structure The donor layer (P3HT) was coated followed by the acceptor layer (PCBM) The difference of the hydrophilicity between the two materials resulted in forming a PCBM nanostructure on the P3HT layer and creating more donor/acceptor interfaces which is so called the “surface heterojunction”OSC The FF and Jsc of the designed OSC were increased and the PCE was improved from 2 80% to 4 38% 4 A nanostructure was also imprinted on the hole transport layer (PEDOT: PSS) to study the influence of the FF and Jsc However the improvement of the FF and Jsc was not as apparent as that of the nanostructure imprinted on the ZnO layer Therefore both the PEDOT: PSS and the ZnO layer were imprinted with nanostructures and the final PCE increased from 2 60% to 3 25% 5 The thermally evaporated Ag electrode was also replaced with the high conductive polymer solution PH1000 to achieve all-solution procedure for fabricating OSCs The optical and electrical properties of the PH1000 were investigated and compared with the Ag electrode The PCE of the resulting OSC reached 1 55% owing to the decreasing Jsc 6 An optical film which duplicated the prism structure of a brightness enhancement film (BEF) in the LCD was added in the all-solution-processed OSC to reflect the incident light and increase the light path in the active layer The Jsc was increased and the PCE of the all-solution-processed OSC also increased from 1 55% to 1 90% after adding the optical film

Date of Award	2015 Jan 12
Original language	English
Supervisor	Chie Gau (Supervisor)