Stability Of Organic Solar Cells Research Articles

Light-induced degradation of fullerenes in organic solar cells: a case study on TQ1:PC71BM

The stability of organic solar cells (OSCs) is critical for practical applications of this emerging technology.

High-efficiency and air stable fullerene-free ternary organic solar cells

Fullerene-free acceptors and ternary strategy have aroused extensive attention due to their great potential for improving efficiency and stability of organic solar cells (OSCs). Here, we demonstrate high-efficiency and air stable OSCs by combining the benefits of fullerene-free acceptors and ternary strategy. A polymer acceptor N2200 as the third component is incorporated with PBDB-T:ITIC to fabricate fullerene-free ternary OSCs, which achieve an outstanding power conversion efficiency (PCE) of 11.41% and excellent stability in air conditions. Compared with the binary cells, the performance improvement of ternary OSCs is mainly attributed to the enhanced photon harvesting and optimized morphology of active layers. Replacing ITIC by a similar acceptor ITIC-Th or IT-M in the ternary OSCs, the optimized PCE of 11.40% or 12.10% can be achieved for PBDB-T:ITIC-Th:N2200-based or PBDB-T:IT-M:N2200-based cells, respectively.

Enhanced thermal stability of organic solar cells comprising ternary D-D-A bulk-heterojunctions

Ternary absorber blends have recently been identified as promising concepts to spectrally broaden the absorption of organic bulk-heterojunction solar cells and hence to improve their power conversion efficiencies. In this work, we demonstrate that D-D-A ternary blends comprising two donor polymers and the acceptor PC61BM can also significantly enhance the thermal stability of the solar cell. Upon harsh thermal stress at 120 °C for 2 h, the ternary solar cells show only a minor relative deterioration of 10%. Whereas the polymer/fullerene blend PTB7-Th:PC61BM is rather unstable under these conditions, its degradation was efficiently suppressed by incorporating the near infrared-absorbing polymer PDTP–DFBT. Spectroscopic ellipsometry investigations and an effective medium analysis of the ternary absorber blend revealed that the domain conformation in presence of PDTP–DFBT remains stable whereas the domain conformation changes in its absence. The ternary PTB7-Th:PDTP–DFBT:PC61BM solar cells yield thermally stable power conversion efficiencies of up to 6%.

Enhancing Efficiency and Stability of Organic Solar Cells by UV Absorbent

A new type of high boiling‐point additive, UV absorbent benzophenone (BP), is reported which can simultaneously improve the efficiency and stability of fullerene and nonfullerene organic solar cells (OSCs). After the addition of BP, the power conversion efficiencies (PCEs) of nonfullerene OSCs based on FTAZ: ITIC‐Th is increased from 8.5 to 9.4%, and is further increased to 10.3% by employing inverted geometry. Meanwhile, the photo‐stability of nonfullerene OSC is improved. After illumination‐aging, the OSCs with BP preserve 79% of the original PCEs, while the OSCs without additives or with 1,8‐diiodooctane only preserve 65 and 58% of their original PCEs, respectively. In addition, BP can also work in fullerene‐based OSCs. After the addition of BP, the efficiency and photo‐stability of the OSCs based on PTB7‐Th: PC71BM are simultaneously enhanced.

Mechanical stability of roll-to-roll printed solar cells under cyclic bending and torsion

The ability of printed organic solar cells (OSCs) to survive repeated mechanical deformation is critical to large-scale implementation. This paper reports an investigation into the mechanical stability of OSCs through bending and torsion testing of whole printed modules. Two types of modules are used that differ slightly in thickness as well as on the basis of the electrode materials: silver nanowires or carbon-based inks. Each type of module is subjected to two different mechanical modes of deformation, bending and torsion, of several thousand cycles per module using a purpose-built robotic device. Analysis of the distribution of stress in the devices performed by finite-element modeling predicts the locations of failure. Failure upon bending originates at the laser-cut edges of the modules from shear at the clamp/module interface leading to crazing of the plastic barrier encapsulant foils. This crazing leads to eventual delamination due first to decohesion of the active layer at the edge of the modules and later to deadhesion between the PEDOT:PSS (electrode) and P3HT:PCBM (semiconductor) layers. The torsion mode imposes greater stresses than the bending mode and thus leads to failure at fewer strain cycles. Failure during torsion occurs through crack propagation initiated at stress concentrations on the edges of the module that were imposed by their rectangular geometry and ultimately leads to bifurcation of the entire module. Rather than the differences in electrode materials, the differences in survivability between the two types of modules are attributed mostly to the thickness of the substrate materials used, with the thinner substrate used in the carbon-based modules (~160µm) failing at fewer strain cycles than the substrate used in the silver-nanowire-based modules (~190µm). Taken together, the results suggest ways in which the lifetimes of devices can be extended by the layouts of modules and choices of materials.

Crosslinked Semiconductor Polymers for Photovoltaic Applications

Organic solar cells (OSCs) have achieved much attention and meanwhile reach efficiencies above 10%. One problem yet to be solved is the lack of long term stability. Crosslinking is presented as a tool to increase the stability of OSCs. A number of materials used for the crosslinking of bulk heterojunction cells are presented. These include the crosslinking of low bandgap polymers used as donors in bulk heterojunction cells, as well as the crosslinking of fullerene acceptors and crosslinking between donor and acceptor. External crosslinkers often based on multifunctional azides are also discussed. In the second part, some work either leading to OSCs with high efficiencies or giving insight into the chemistry and physics of crosslinking are highlighted. The diffusion of low molar mass fullerenes in a crosslinked matrix of a conjugated polymer and the influence of crosslinking on the carrier mobility is discussed. Finally, the use of crosslinking to make stable interlayers and the solution processing of multilayer OSCs are discussed in addition to presentation of a novel approach to stabilize nanoimprinted patterns for OSCs by crosslinking.

Annealing and Environment Effects on Energy Efficiency and Parameter Stability of Organic Solar Cells

Annealing and Environment Effects on Energy Efficiency and Parameter Stability of Organic Solar Cells

XPS Analysis of the Improved Operational Stability of Organic Solar Cells Using a V2O5 and PEDOT:PSS Composite Layer: Effect of Varied Atmospheric Conditions

This work investigates the enhanced stability of organic solar cells (OSCs) fabricated with a hybrid hole-transport layer (HTL) incorporating vanadium pentaoxide (V2O5) nanoparticles in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). OSCs have been fabricated in controlled and ambient atmospheric conditions by employing a pristine PEDOT:PSS HTL and its hybrid variant. Stability and degradation analyses were carried out by using photovoltaic and X-ray photoelectron spectroscopy (XPS) measurements, respectively. Normalized photovoltaic characteristics showed that OSCs with hybrid HTL outperformed the pristine device and retained their performance as compared to their pristine counterparts when the fabrication was carried out in a nitrogen-filled glovebox and devices were tested after encapsulation for 7 days. However, OSCs that were fabricated and characterized in ambient air showed severe degradation in photovoltaic performance, mainly due to a drastic decay in the short circuit curren...

Self-Assembled Organic Materials for Photovoltaic Application.

Organic photovoltaic cells based on bulk-heterojunction architecture have been a topic of intense research for the past two decades. Recent reports on power conversion efficiency surpassing 10% suggest these devices are a viable low-cost choice for a range of applications where conventional silicon solar cells are not suitable. Further improvements in efficiency could be achieved with the enhanced interaction between the donor and acceptor components. Effective utilization of supramolecular interactions to tailor and manipulate the communication between the components in the blend is a good strategy towards this end. Literature reports suggest that the long-term stability of organic solar cells, a major hurdle for commercial applications, can also be partially addressed by generating stable supramolecular nanostructures. In this review, we have made an attempt to summarize advances in small molecule, oligomer and polymer based systems, wherein supramolecular interactions such as hydrogen-bonding, pi-pi stacking, and dipole-dipole are explored for realizing stable and efficient bulk-heterojunction solar cells.

Abnormal strong burn-in degradation of highly efficient polymer solar cells caused by spinodal donor-acceptor demixing

The performance of organic solar cells is determined by the delicate, meticulously optimized bulk-heterojunction microstructure, which consists of finely mixed and relatively separated donor/acceptor regions. Here we demonstrate an abnormal strong burn-in degradation in highly efficient polymer solar cells caused by spinodal demixing of the donor and acceptor phases, which dramatically reduces charge generation and can be attributed to the inherently low miscibility of both materials. Even though the microstructure can be kinetically tuned for achieving high-performance, the inherently low miscibility of donor and acceptor leads to spontaneous phase separation in the solid state, even at room temperature and in the dark. A theoretical calculation of the molecular parameters and construction of the spinodal phase diagrams highlight molecular incompatibilities between the donor and acceptor as a dominant mechanism for burn-in degradation, which is to date the major short-time loss reducing the performance and stability of organic solar cells.

Improved mechanical adhesion and electronic stability of organic solar cells with thermal ageing: the role of diffusion at the hole extraction interface

Organic photovoltaic solar cells are a promising option for cheap, renewable energy, but must improve in their stability.

Enhancing Efficiency and Stability of Organic Solar Cells by UV Absorbent

Enhancing Efficiency and Stability of Organic Solar Cells by UV Absorbent

Enhancing the performance and stability of organic solar cells using solution processed MoO3 as hole transport layer

Efficient and stable poly(3-hexylthiophene) (P3HT):indene-C60 bisadduct (ICBA) based bulk-heterojunction (BHJ) organic solar cells (OSCs) with solution processed MoO3 (s-MoO3) as hole transport layer were fabricated.

Toward High‐Temperature Stability of PTB7‐Based Bulk Heterojunction Solar Cells: Impact of Fullerene Size and Solvent Additive

The use of fullerene as acceptor limits the thermal stability of organic solar cells at high temperatures as their diffusion inside the donor leads to phase separation via Ostwald ripening. Here it is reported that fullerene diffusion is fully suppressed at temperatures up to 140 °C in bulk heterojunctions based on the benzodithiophene‐based polymer (the poly[[4,8‐bis[(2‐ethylhexyl)oxy]‐benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]‐thieno[3,4‐b]thiophenediyl]], (PTB7) in combination with the fullerene derivative [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC70BM). The blend stability is found independently of the presence of diiodooctane (DIO) used to optimize nanostructuration and in contrast to PTB7 blends using the smaller fullerene derivative PC70BM. The unprecedented thermal stability of PTB7:PC70BM layers is addressed to local minima in the mixing enthalpy of the blend forming stable phases that inhibit fullerene diffusion. Importantly, although the nanoscale morphology of DIO processed blends is thermally stable, corresponding devices show strong performance losses under thermal stress. Only by the use of a high temperature annealing step removing residual DIO from the device, remarkably stable high efficiency solar cells with performance losses less than 10% after a continuous annealing at 140 °C over 3 days are obtained. These results pave the way toward high temperature stable polymer solar cells using fullerene acceptors.

Stability of Organic Solar Cells: The Influence of Nanostructured Carbon Materials

Organic solar cells (OSCs) are lightweight, have adaptable colors, and can be produced in low‐cost procedures on transparent and flexible surfaces. This makes them attractive for markets in which other technologies cannot compete, for example in architectural and consumer product integration. However, both efficiencies and long term operational stability of OSCs do not yet meet the standards set by their inorganic counterparts. This review compiles the growing knowledge about how nanostructured carbon materials, such as fullerenes and carbon nanotubes, decisively influence the operational stability of organic photovoltaics. Firstly, important degradation pathways are introduced and a differential detection scheme is set up to find the dominant loss channel by means of state‐of‐the‐art characterization methods. Then, fullerenes ability to both stabilize and destabilize the donor polymer against photooxidation via different mechanisms (e.g., inner filter effect or radical scavenging) is examined in detail. The “burn‐in” problem, an initial rapid efficiency loss in PC60BM‐based OSCs, is shown to derive from light‐induced PC60BM dimerization, an effect that can also be positively exploited to reduce thermal degradation. Finally, thermal stabilization via additional approaches involving the fullerene derivative, such as crosslinking or incorporation into block copolymers, is presented.

Stability in organic solar cells with Ag/pentacene anode buffer under repetitive illumination

The degradation phenomenon in small-molecule organic solar cells (OSCs) with a structure of indium-tin oxide (ITO, anode)/anode buffer/copper phthalocyanine (CuPc, donor)/fullerene (acceptor)/bathocuproine (cathode buffer)/Ag (cathode) was experimentally investigated. Two kinds of anode buffer layers, a 2-nm-thick pentacene layer and a 0.5-nm-thick Ag layer, were examined. The devices were subjected to repetitive illumination stress through the transparent ITO electrode in air. The ultra-thin Ag layer enhanced the ability of the devices to withstand the illumination stress. A thinner Ag layer resulted in better device performance. Resonant light absorption in the nanometer-scale Ag clusters probably accumulates trapped electrons near the ITO/CuPc interface, shrinks the depletion layer, enhances tunneling injection of holes, and suppresses the S-shaped kink during the illumination. The thin pentacene layer provides good ohmic contact between the anode and the CuPc layer, resulting in a larger short-circuit current. OSCs fabricated with both Ag and pentacene anode buffer layers exhibited only a 10% decrease in power conversion efficiency at 60 repetitions, whereas OSCs without an anode buffer layer exhibited a decrease of approximately 45%. The large decrease in efficiency was dominated by the decrease in the fill factor.

Air-processed high performance ternary blend solar cell based on PTB7-Th:PCDTBT:PC70BM

Ternary bulk heterojunctions (BHJs) are promising candidates that can improve the power conversion efficiencies (PCEs) of organic solar cells (OSCs). In this paper, a ternary OSC with two donors, including one wide bandgap polymer poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT), one low bandgap polymer Poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-co-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th), and one acceptor [6,6]-phenyl C70 butyric acid methyl ester (PC70BM), is fabricated in atmospheric conditions. By incorporating a 20% content of PCDTBT, an optimized PCE of 7.86% for ternary OSC is characterized by a short-circuit current density (Jsc) of 15.21 mA cm−2, a fill factor of 69.70% and an open-circuit voltage (Voc) of 0.74 V. The Voc values increased steadily from 0.73 to 0.86 V as the increase of PCDTBT fraction, which indicates that the Voc of ternary OSC is not limited by the smallest one of the corresponding binary OSC. We show that the Jsc of the ternary OSC is better than those of the binary OSC in virtue of the complementary polymer absorption and cascade energy levels, as well as optimized morphology of the ternary system. Furthermore, the lifetime of the devices with PCDTBT is greatly enhanced. This work indicates that two donors (PTB7-Th/PCDTBT) ternary BHJs system provide a simple and effective method to improve the performance and also the stability of OSCs.

Enhanced photocurrent and stability of organic solar cells using solution-based TS-CuPc interfacial layer

Copper phthalocyanine-3,4′,4″,4‴ tetra-sulfonated acid tetrasodium salt (TS-CuPc) are promising interfacial materials for organic photovoltaics (OPVs) because of their electrical properties, solution process ability and stability. In this article, we report the fabrication of poly(3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester (P3HT:PCBM) OPV devices incorporating solution-based TS-CuPc as electron transport layers that show promising enhancements of the device photocurrent and stability. We also discuss the impact of the mechanism of Photochemical and photophysical behavior and all parameters on device performance as well as the ambient degradation of these devices. In these results we showed charge extraction improvement by the use of the TS-CuPc.

Influence of Physical Load on the Stability of Organic Solar Cells with Polymer : Fullerene Bulk Heterojunction Nanolayers

Influence of Physical Load on the Stability of Organic Solar Cells with Polymer : Fullerene Bulk Heterojunction Nanolayers

ChemInform Abstract: Stability of Organic Solar Cells: Challenges and Strategies

AbstractReview: factors limiting the stability and recent developments in strategies to increase the stability of organic solar cells; 381 refs.