Abstract
In the present study, we have compared the device performance of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thio-phene-)-2-carb-oxylate-2-6-diyl)] (PTB7-Th):phenyl-C71-butyric acid methyl ester (PCBM) organic solar cells (OSCs) in an inverted geometry with ZnO, a bilayer of ZnO and Ba(OH)2 [ZnO/Ba(OH)2] and a nanocomposite of ZnO and Ba(OH)2 [ZnO:Ba(OH)2] as electron transport layers (ETLs). Our study reveals that the performance of the devices with the ZnO/Ba(OH)2 and ZnO:Ba(OH)2 nanocomposite as ETL supersedes that of devices with only ZnO as ETL. The plausible reasons for the improved performance of these devices are identified using morphological studies, contact angle measurements, X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and photo-electrochemical impedance spectroscopy (EIS) measurements. It is observed that films of ZnO/Ba(OH)2 and ZnO:Ba(OH)2 nanocomposites have a low work function and are slightly more smooth and hydrophobic than ZnO films. This might have suppressed the charge recombination and thereby improved the charge collection as has been confirmed by EIS measurements.
Highlights
Solution processed bulk-heterojunction organic solar cells (OSCs), which consist of a conjugated polymer as an electron donor and fullerene and/or polymer as an acceptor, are widely regarded as an emerging PV technology and offer many advantages such as mechanical exibility, low-cost, light weight, low energy consuming roll-to-roll manufacturing process, etc.[1,2,3,4,5] Over the years, to increase the power conversion efficiency (PCE) of OSCs, various strategies have been used
Our study reveals that the performance of the devices with ZnO/ Ba(OH)[2] and ZnO:Ba(OH)[2] nanocomposite as electron transport layers (ETLs) supersedes that of devices with only ZnO as ETL
For preparation of ZnO:Ba(OH)[2] nanocomposite, ZnO stock solution was mixed with a set amount of Ba(OH)[2] solution (3, 6, Fig. 1 (a) Schematic of PTB7-Th:PCBM OSCs in an inverted geometry with ZnO, ZnO/Ba(OH)[2] and ZnO:Ba(OH)[2] nanocomposite as ETLs (b) energy levels of materials used in the solar cell device
Summary
Solution processed bulk-heterojunction organic solar cells (OSCs), which consist of a conjugated polymer as an electron donor and fullerene and/or polymer as an acceptor, are widely regarded as an emerging PV technology and offer many advantages such as mechanical exibility, low-cost, light weight, low energy consuming roll-to-roll manufacturing process, etc.[1,2,3,4,5] Over the years, to increase the power conversion efficiency (PCE) of OSCs, various strategies have been used This includes designing and developing new donor and/or acceptor molecules having wide absorption spectra and/or employing various aspects of device and interface engineering such as use of solvent additives for photoactive layer processing, incorporation of metals, dielectric and/or semiconducting nanoparticles (NPs) in the photoactive layer, use of buffer layers like electron and/or hole transport layers, etc.[6,7,8,9,10,11,12] It has been demonstrated in the past that the careful selection of electron and/or hole transport layers can improve the PCE by 2–3% for the same donor:acceptor bulk-heterojunction system.[12,13,14,15,16,17]. As obtained solutions were ltered by a nylon lter with a diameter of 0.45 mm prior to the spin-cast
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