Degradation of Sexithiophene Cascade Organic Solar Cells

Abstract

fl exibility or light weight required for fl exible OPV. Atomic layer deposited (ALD) oxide thin-fi lms (e.g. SiO x , AlO x ) provide fl exibility and low WVTR rates at the same time. [22][23][24] This work is motivated by two factors: First, a lifetime study for cascade organic solar cells (CSCs) under ambient climate conditions has not been performed up to now, making the evaluation of their applicability diffi cult. Second, only a few publications show highly effi cient organic solar cells on silver nanowire electrodes. Beyond that, all devices exhibiting a PCE >5% on AgNW electrodes used polymer donors. [25][26][27] In this study, we show aging experiments on organic solar cells with the small molecules α-6T/SubNc/SubPc as cascade. [ 10 ] We compare rigid glass-glass encapsulated devices with ITO bottom electrodes to fully fl exible devices. AgNWs are utilized as transparent electrode, ALD thin-fi lms of alumina serve as fl exible ultra-barrier. The planarization of AgNWs is challenging, as they exhibit high surface roughness which usually causes the organic thin-fi lm device to shunt. Many different planarization techniques have been successfully employed using poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), metal oxides, or small molecules. [ 17,[28][29][30][31][32] Another method uses a peel-off process whereby the silver nanowires are buried in a polymer substrate. [ 25,[33][34][35] We employ the AgNW planarization concept recently demonstrated by Cui et al., [ 36 ] where the AgNWs are buried in the UV-curable optical adhesive "NOA63". This polymer serves as ultrathin and ultrafl exible substrate for the highly conductive AgNW network. Figure 1 shows the electrode fabrication and characterization by means of topographical and optical analysis. Silver nanowires with 35 nm diameter (NW35) are used to transfer the NOA63 into a conductive substrate (details can be found in the Experimental Section).Atomic force microscopy (AFM) measurements reveal that the root-mean-square roughness of the electrode is in the range of 1 to 2 nm (Figure 1 B). Furthermore, the strong phase contrast in Figure 1 C shows that AgNWs protrude from the NOA63 surface. This guarantees an electrical contact to adjacent conductive layers. A sheet resistance ( R S ) of (18.5 ± 0.2) Ω/sq is measured for this electrode even though the maximum processing temperature is only 80 °C. The electrode exhibits a total transmission of 84.5% at a wavelength of 550 nm which is comparable to NW35 on glass. However, plasmonic nanowire absorption, which is already present in the neat glass/NW35 electrode, broadens upon embedding in the polymer. This stronger plasmonic absorption in the spectral region between 350 and 500 nm reduces the average total transmission in the visible light spectrum T av to 82.8% as compared to 83.9% of NW35 on glass. Although ITO on glass exhibits a T av of 84.3%, its R S of 26 Ω/sq is higher than for the NW35 electrode.This ultrasmooth, highly conductive, and transparent AgNW electrode is well suitable for ...

Boron Subphthalocyanines and Silicon Phthalocyanines for Use as Active Materials in Organic Photovoltaics

“…In 2014, Cnops et al . demonstrated the validity and high performance of a three‐layer energy cascade device architecture (Figure ), which became the basis of several follow‐up studies . Cl‐Cl n BsubNc and Cl‐BsubPc were applied as dual electron acceptors paired with α‐6T, whereby exciton dissociation follows a two‐step process.…”

“…Improving durability and lifetime of OPVs is a well‐known challenge in the field, but has received comparatively little attention in literature. Ageing experiments were conducted on the α‐6T/BsubNc/BsubPc energy cascade solar cell that was first demonstrated by Cnops et al . An indoor climate chamber with a mounted solar simulator was used to age the OPVs, and different encapsulation architectures were compared.…”

Efficient flexible organic photovoltaics using silver nanowires and polymer based transparent electrodes

“…The device is protected by a flexible 20 nm AlO x (Water vapor transmission rate of 2 Â 10 À5 g/m 2 day) thin-film encapsulation [26]. A maximum PCE of 6.91% is achieved; the degradation of OPVs with this encapsulation has been investigated by Bormann et al [27]. For checking the electrical stability of AgNW/PEDOT: PSS as electrode for flexible devices, a bending test is performed in ambient condition.…”

“…For the top encapsulation, an equivalent thin-film is deposited on 125 mm planarised Teonex PEN (Dupont Teijin Films Ltd.,UK). In a glovebox, this barrier film is directly laminated onto the OPV devices using a barrier adhesive film (tesa SE, Germany) [27,30], which contains a latent getter against lateral oxygen and water diffusion. Current voltage measurements are measured by using a source measurement unit 2400 SMU (Keithley, USA) and simulated AM 1.5G sun light (16Se150 V.3 by Solar Light Co., USA) taking spectral mismatch into account.…”

Flexible, light trapping substrates for organic photovoltaics

“…28 Degradation of OPVs with this encapsulation was previously investigated, and AlO x layer still showed similar WVTR value without cracking after 300 bending cycles with the bending radius of 15 mm. 31 To check the stability of the solar cell on the PET substrates, a bending test is performed in the ambient condition. The devices remain working after bending with 10 mm radius without any degradation, similar to a previous study.…”