Stability Of Organic Photovoltaics Research Articles

Outdoor Stability of Chloro–(Chloro)n–Boron Subnaphthalocyanine and Chloro–Boron Subphthalocyanine as Electron Acceptors in Bilayer and Trilayer Organic Photovoltaics

In the field of organic photovoltaics (OPVs), outdoor stability research has lagged behind material development and device engineering. Testing protocols established at the International Summit of OPV Stability (ISOS) have stimulated some stability research, but these studies are almost exclusively limited to already-refined devices made with already-commercialized materials. If OPV materials were tested outdoors during small-scale stages, stability issues could be detected earlier in the development cycle. Chloro–(chloro)n–boron subnaphthalocyanine (Cl–ClnBsubNc) is a material with high OPV performance but has not previously been tested outdoors. An OPV power conversion efficiency of 8.4% has been previously demonstrated for a trilayer stack containing α-sexithiophene, Cl–ClnBsubNc, and chloro–boron subphthalocyanine (Cl–BsubPc). Building on the most advanced ISOS outdoor testing protocols (ISOS-O3), we assess the outdoor stability of small-scale bilayer and trilayer OPVs while establishing an improved stability screening method for future derivatives. The outdoor stability of Cl–ClnBsubNc is determined to be comparable to that of Cl–BsubPc.

Hydrogen plasma-treated MoSe2 nanosheets enhance the efficiency and stability of organic photovoltaics.

In this paper we report the effect on the power conversion efficiency (PCE) and stability of photovoltaic devices after incorporating hydrogenated two-dimensional (2D) MoSe2 nanosheets into the active layer of bulk heterojunction (BHJ) organic photovoltaics (OPV). The surface properties of 2D MoSe2 nanosheets largely affect their dispersion in the active layer blend and, thus, influence the carrier mobility, PCE, and stability of corresponding devices. We treated MoSe2 nanosheets with hydrogen plasma and investigated their influence on the polymer packing and fullerene domain size of the active layer. For the optimized devices incorporating 37.5 wt% of untreated MoSe2, we obtained a champion PCE of 9.82%, compared with the champion reference PCE of approximately 9%. After incorporating the hydrogen plasma-treated MoSe2 nanosheets, we achieved a champion PCE of 10.44%-a relative increase of 16% over that of the reference device prepared without MoSe2 nanosheets. This PCE is the one of the highest ever reported for OPVs incorporating 2D materials. We attribute this large enhancement to the enhanced exciton generation and dissociation at the MoSe2-fullerene interface and, consequently, the balanced charge carrier mobility. The device incorporating the MoSe2 nanosheets maintained 70% of its initial PCE after heat-treatment at 100 °C for 1 h; in contrast, the PCE of the reference device decreased to 60% of its initial value-a relative increase in stability of 17% after incorporating these nanosheets. We also incorporated MoSe2 nanosheets (both with and without treatment) into a polymer donor (PBDTTBO)/small molecule (IT-4F) acceptor system. The champion PCEs reached 7.85 and 8.13% for the devices incorporating the MoSe2 nanosheets with and without plasma treatment, respectively-relative increases of 8 and 12%, respectively, over that of the reference. These results should encourage a push toward the implementation of transition metal dichalcogenides to enhance the performances of BHJ OPVs.

Enhanced Device Performance and Stability of Organic Photovoltaics Incorporating a Star-Shaped Multifunctional Additive

In this study, we developed a star-shaped diketopyrrolopyrrole (DPP)-based additive as an efficient morphology fixing agent for organic photovoltaics (OPVs). This conjugated small molecule, DPPTPTA, has four arms, with two terphenyl units and four alkyl azide groups. We tested the behavior of DPPTPTA after incorporating it into an active layer comprising poly[4,8-bis(5-(2-ethylhexyl)thien-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene)-2-carboxylate-2,6-diyl)] (PTB7-Th) and the PC61BM fullerene. Atomic force microscopy, UV–vis spectroscopy, optical microscopy, photoluminescence (PL) spectroscopy, and an X-ray photoelectron spectroscopy (XPS) depth profile revealed the effects of the resulting morphological change on the device performance and thermal stability. Compared with the PTB7-Th:PC61BM device prepared without DPPTPTA, the device incorporating this additive exhibited an increase in the power conversion efficiency (from 6.7 to 8.2%) and improved the...

Alcohol-Soluble Cross-Linked Poly(nBA)n-b-Poly(NVTri)m Block Copolymer and Its Applications in Organic Photovoltaic Cells for Improved Stability

In this study, a series of alcohol-soluble cross-linked block copolymers (BCPs) consisting of poly( n-butyl acrylate) (poly( nBA)) and poly( N-vinyl-1,2,4-triazole) (poly(NVTri)) blocks with different individual functions and lengths are designed and developed. These presynthesized cross-linked BCPs (PBA n-Tri m) were, for the first time, revealed to exhibit many advantages in serving as the electron-extraction layer (EEL) for organic photovoltaics (OPVs). The cross-linked BCPs possessed intense ionic functionality, showing well capability to form effective interfacial dipoles at the indium tin oxide interface to facilitate the charge extraction at the corresponding interface. Furthermore, it also consisted a core-shell structure, wherein the polar poly(NVTri) core was well protected by the poly( nBA) shell to endow improved robustness against solvent erosion and thermal/photo inputs. Consequently, the PBA70-Tri30 device yielded a decent power conversion efficiency of 8.03% with a Voc of 0.83 V, much exceeding the performance of the control device without using any EEL. Moreover, this device showed superior thermal stability/photostability. More than 80% of its initial performance was retained after being heated at 60 °C for 1000 h or exposed under continuous illumination (1 sun) for 1000 h, greatly surpassing the lifetime of the control device and the reference device using a common poly[(9,9-bis(3'-( N, N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) EEL. The results revealed the merit of using cross-linked BCPs in improving the long-term stability of OPVs.

UV-Cross-linkable Donor-Acceptor Polymers Bearing a Photostable Conjugated Backbone for Efficient and Stable Organic Photovoltaics.

High-performance photovoltaic polymers bearing cross-linkable function together with a photorobust conjugated backbone are highly desirable for organic solar cells to achieve both high device efficiency and long-term stability. In this study, a family of such polymers is reported based on poly[(2,5-bis(2-hexyldecyloxy)phenylene)- alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[ c]-[1,2,5]thiadiazole)] (PPDT2FBT), a high-performance photovoltaic donor-acceptor polymer, with different contents of terminal vinyl-appended side chains for cross-linking. The polymers were named PPDT2FBT-V x and prepared by varying the feeding ratio ( x mol %, x = 0, 5, 10, and 15) of the vinyl-appended monomer in polymerization. It was found that the vinyl integration did not sacrifice the original high photovoltaic performance of the polymers, as evidenced by comparable average power conversion efficiencies (PCEs) (6.95, 7.02, and 7.63%) observed for optimized devices based on PPDT2FBT-V0, PPDT2FBT-V5, and PPDT2FBT-V10, respectively, in blending with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). Unlike thermal cross-linking that greatly reduced device efficiency, UV cross-linking has proven to be an effective way to achieve both high device efficiency and thermostability for PPDT2FBT-V10 solar cells. UV-cross-linked PPDT2FBT-V10 solar cells displayed an initial average PCE of 5.28% and almost no decrease upon heat treatment at 120 °C for 40 h. Morphology studies revealed that UV-cross-linking did not only alter initial nanophase separation but also suppressed morphology evolution by aggregation in bulk heterojunction blend films. Photo-cross-linking requires material photostability. It is therefore worthwhile to note that these polymers and their blends with PC71BM were found to be extremely photostable, even upon continuous exposure to concentrated sunlight (up to 200 suns), and UV-cross-linking does not hamper this photostability. Further studies found that the devices fabricated with the UV-cross-linked PPDT2FBT-V10/PC71BM active layer can endure continuous light exposure to a solar simulator without deteriorating their performance.

Triptycene as a Supramolecular Additive in PTB7:PCBM Blends and Its Influence on Photovoltaic Properties.

Additives play an important role in modifying the morphology and phase separation of donor and acceptor molecules in bulk heterojunction (BHJ) solar cells. Here, we report triptycene (TPC) as a small-molecule additive for supramolecular control of phase separation and concomitant improvement of the power conversion efficiency (PCE) of PTB7 donor and fullerene acceptor-based BHJ polymer solar cells. An overall 60% improvement in PCE is observed for both PTB7:PC61BM and PTB7:PC71BM blends. The improved photovoltaic (PV) performance can be attributed to three factors: (a) TPC-induced supramolecular interactions with donor:acceptor components in the blends to realize a nanoscale phase-separated morphology; (b) an increase in the charge transfer state energy that lowers the driving force for electron transfer from donor to acceptor molecules; and (c) an increase in the charge carrier mobility. An improvement in efficiency using TPC as a supramolecular additive has also been demonstrated for other BHJ blends such as PBDB-T:PC71BM and P3HT:PCBM, implying the wide applicability of this new additive molecule. A comparison of the photostability of TPC as an additive for PTB7:PCBM solar cells to that of the widely used 1,8-diiodooctane additive shows ∼30% higher retention of PV performance for the TPC-added solar cells after 34 h of AM 1.5G illumination. The results obtained suggest that the approach of using additives that can promote supramolecular interactions to modify the length scale of phase separation between donor and acceptor is very promising and can lead to the development of highly efficient and stable organic photovoltaics.

Current Status of Outdoor Lifetime Testing of Organic Photovoltaics.

Performance degradation is one of the key obstacles limiting the commercial application of organic photovoltaic (OPV) devices. The assessment of OPV stability and lifetime are usually based on simulated degradation experiments conducted under indoor conditions, whereas photovoltaic devices experience different environmental conditions under outdoor operation. Besides the intrinsic degradation of OPV devices due to the evolution of optoelectronic and morphological structure during long‐term operation, outdoor environmental changes can impose extra stresses and accelerate the degradation of OPV modules. Although outdoor studies on long‐term OPV stability are restricted by the long data collection times, they provide direct information on OPV stability under mixed degradation stresses and are therefore invaluable from the point of view of both research and practical application. Here, an overview of the current status of outdoor lifetime studies of OPVs is provided. After a summary of device lifetime extrapolated from indoor studies, outdoor lifetime testing platforms are introduced and the operational lifetime of various OPV devices are reviewed. The influence of climate and weather parameters on device performance and burn‐in phenomena observed during the degradation of OPVs is then discussed. Finally, an outlook and directions for future research in this field are suggested.

Performance and stability of semitransparent OPVs for building integration: A benchmarking analysis

Semitransparent (ST) organic photovoltaics (OPVs) are demonstrating great potential for building integration applications, especially in windows. For that purpose, ST-OPVs should achieve adequate transparency and performance stability. In this regard, the present research deals with the experimental performance of three different building-integrated ST-OPV technologies (technology A: developed in the frame of the present study; technologies B and C: commercial modules). More specifically, spectral transmittance and electrical measurements have been conducted in order to determine the characteristics of the modules for building integration and electricity generation purposes. Results regarding the transmittance reveal that technology A outperforms technologies B and C. The stability analysis of the modules verifies that module C is the most stable one with almost no decrease (3.6%) in the power conversion efficiency (PCE). Furthermore, the PCE of technology B is slightly higher than in the case of technology C, which experiences a PCE degradation of about 10–15% over the whole time period. Finally, technology A presents a 20% reduction in PCE at around 500 h.

Blue photon management by inhouse grown ZnO:Al cathode for enhanced photostability in polymer solar cells

We report the improvement in photostability of P3HT:PC60BM based bulk heterojunction solar cells deposited on Al-doped ZnO as a cathode layer replacing ITO as regularly used TCO in cells with N-I-P configuration. We experimentally and theoretically demonstrate that use of thicker ZnO:Al as cathode can successfully cut down the rate of photodegradation in short circuit current by ~40% and open circuit voltage by ~30% compared to the control device made on ITO based cathode. This effective reduction in photodegradation is understood to be coming from the absorption of ultraviolet and blue photon in the cathode layer itself. The loss in short circuit current due to the loss of blue photon in EQE is compensated by higher FF (lower series resistance) due to thicker ZnO:Al layer resulting in final device efficiency almost uncompromised with added benefit of reduced photo degradation. The experimental results are supported with optical simulations which show more absorption in the short wavelength region for the thicker ZnO films, compared to ITO films, deposited on glass substrates. This work also proposes using ZnO:Al cathode as a template for random textured front surface to potentially increase short circuit current by increase in photon absorption in active layer matrix by light scattering techniques. Our results provide an inexpensive pathway for improving the stability of organic photovoltaics without compromising the device performance.

Degradation in perovskite solar cells stored under different environmental conditions

Investigations carried out on the degradation of perovskite solar cells (PSCs) stored in different open air environmental conditions are reported here. The solar cells were stored in the open in the dark inside the laboratory (relative humidity 47 ± 5%, temperature 23 ± 4 °C), under compact fluorescent lamp (CFL) illumination (irradiance 10 mW cm2, relative humidity 47 ± 5%, temperature 23 ± 4 °C) and under natural sunlight outside the laboratory. In the outdoor storage situation the surrounding conditions varied from time to time and the environmental conditions during the day (irradiance 100 mW/cm2, relative humidity ~18%, temperature ~45 °C at noon) were entirely different from those at night (irradiance 0 mW/cm2, relative humidity ~66%, temperature ~16 °C at midnight). The photovoltaic parameters were measured from time to time inside the laboratory as per the International Summit on Organic Photovoltaic Stability (ISOS) protocols. All the photovoltaic parameters, such as short circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF) and power conversion efficiency (PCE), of the solar cells stored outdoors decayed more rapidly than those stored under CFL or in the dark. The solar cells stored in the dark exhibited maximum stability. While the encapsulated solar cells stored outdoors were completely dead after about 560 h, the solar cells stored under CFL illumination retained >60% of their initial efficiency even after 1100 h. However, the solar cells stored in the dark and tested up to ~1100 h did not show any degradation in PCE but on the contrary exhibited slight improvement, and this improvement was mainly because of improvement in their Voc. Rapid degradation in the open air outside the laboratory under direct sunlight compared with the dark and CFL storage has been attributed to high temperature during the day, high humidity at night, high solar illumination intensity and the presence of ultra-violet and infra-red radiation in incident solar light. Under CFL storage the top Ag electrode decomposed and reacted with the active layer. The decomposition and reaction of Ag electrode was accelerated in the outdoor conditions under direct sunlight. These results suggest that Ag is a good electrode material for efficient PSCs but is not good for their long term stability.

Air-processed organo-metal halide perovskite solar cells and their air stability

We investigate and report here the air stability of air-processed mixed halide CH3NH3PbI3−xClx perovskite solar cells. The solar cells were prepared in planar heterojunction as well as mesoscopic structures using four perovskite precursors having different wt% concentrations, viz. 13.7, 17.5, 24.1 and 38.9 wt%. Compact TiO2 layer (TiO2-bl) was used as electron transport layer, whereas poly(3-hexylthiophene) (P3HT) was used as hole transport layer. All the solar cells were processed in identical conditions. Irrespective of device structures, the higher precursor concentration resulted in larger crystalline grains, which led to higher power conversion efficiency in the solar cells. The solar cells were stored in dark and tested for their stability as per the International Summit on Organic Photovoltaic Stability (ISOS) protocol ISOS-D-1. The degradation profiles of solar cells have also been studied in natural outdoor conditions under direct sunlight as per the ISOS-O-1 protocols. Interestingly, the solar cells having larger perovskite grains exhibited higher efficiency but inferior air stability compared to those having smaller grains. Poorer stability of solar cells having larger perovskite grains has been attributed to poorer morphological and compositional stability of perovskite films.

Outdoor Performance and Stability of Boron Subphthalocyanines Applied as Electron Acceptors in Fullerene-Free Organic Photovoltaics

The outdoor lifetime and performance of organic photovoltaics (OPVs) using boron subphthalocyanine (BsubPc) derivatives as electron-accepting materials is presented. The protocols followed are based on the most advanced level of outdoor testing established by the International Summit on OPV Stability (ISOS). The stability of each BsubPc is compared using three different sets of encapsulated planar heterojunction OPVs, with each set containing a different BsubPc as the electron-accepting layer. The performance and stability of each set is tested outdoors using an epoxy glue and a glass coverslip as protection from the ambient environment. Outdoor testing continued until the OPVs reached 80 or 50% of their original power conversion efficiency, as determined by frequent indoor characterization. OPVs utilizing chloro-BsubPc are shown to exhibit the highest stability and performance, while the stability of the other two BsubPc derivatives is reduced presumably as a result of their phenoxy or phenyl functionali...

Pathway for recovery of photo-degraded polymer solar cells by post degradation thermal anneal

The photo-degradation of polymer solar cells is a critical challenge preventing its commercial deployment. We experimentally fabricate organic solar cells and characterize their degradation under solar simulators in an environmental chamber under nitrogen flow, without exposure to oxygen and moisture. We have developed a thermally stable inverted organic solar cell architecture in which light induced degradation of device characteristics can be reversibly annealed to the pristine values. The stable inverted cells utilized MoOx layers that are thermally treated immediately after their deposition on the organic layer, and before metal cathode deposition. Organic solar cells that are photo-degraded in the presence of oxygen, however show irreversible degradation that cannot be thermally recovered. The decrease of organic solar cell characteristics correlates with increases in mid-gap electronic states, measured using capacitance spectroscopy and dark current. It is likely the photo-induced defect states caused by local H motion from the alkyl chains to the aromatic backbone, can be reversibly annealed at elevated temperatures after photo-degradation. Our results provide a pathway for improving the stability of organic photovoltaics.

Donor-Acceptor Interface Stabilizer Based on Fullerene Derivatives toward Efficient and Thermal Stable Organic Photovoltaics.

An interface stabilizer based on alkylation-functionalized fullerene derivatives, [6, 6]-Phenyl-C61-butyric acid (3,5-bis(octyloxy)phenyl)methyl ester (PCB-C8oc), was successfully synthesized and applied for the active layer of Organic Photovoltaics (OPVs). The PCB-C8oc can replace part of the phenyl-C61-buty-ric acid methyl ester (PCBM) and be distributed on the interface of poly(3-hexylthiophene) (P3HT) and PCBM to form P3HT/PCBM/PCB-C8oc ternary blends, leading to thermally stable and efficient organic photovoltaics. The octyl groups of PCB-C8oc exhibit intermolecular interaction with the hexyl groups of P3HT, and the fullerene unit of PCB-C8oc are in tight contact with PCBM. The dual functions of PCB-C8oc will inhibit the phase separation between electron donor and acceptor, thereby improving the stability of devices under long-time thermal annealing at high temperature. When doped with 10 wt % PCB-C8oc, the power conversion efficiency (PCE) of the P3HT system decreased from 3.54% to 2.88% after 48 h of thermal treatment at 150 °C, whereas the PCE of the reference device without PCB-C8oc dramatically dropped from 3.53% to 0.73%. When doping 10 or 20 wt % PCB-C8oc, the unannealed P3HT/PCBM/PCB-C8oc device achieved a higher PCE than the P3HT/PCBM device without any annealing following the same fabricating condition. For the PTB7/PCBM-based devices, after adding only 5 wt % PCB-C8oc, the OPVs also exhibited thermally stable morphology and better device performances. All these results demonstrate that the utilization of alkyl interchain interactions is an effective and practical strategy to control morphological evolution.

PCDTBT: From Polymer Photovoltaics to Light-Emitting Diodes by Side-Chain-Controlled Luminescence

Poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole) (PCDTBT) is a copolymer composed of alternating thiophene–benzothiadiazole–thiophene (TBT) and carbazole (Cbz) repeat units widely used for stable organic photovoltaics. However, the solubility of PCDTBT is limited, which decreases polymer yield and makes synthesis and purification tedious. Here, we introduce a strategy to increase both solubility and luminescence by the statistical incorporation of additional hexyl side chains at the TBT unit (hex-TBT). An increasing amount of hex-TBT as comonomer from 0 to 100% enhances solubility, leads to backbone torsion, and causes a blue-shift in the absorption and emission spectra. While photovoltaic performance of both PCDTBT:P3HT blends and PCDTBT:PC71BM blends decreases with increasing content of hex-TBT due to weaker and blue-shifted absorption, the luminescence properties can be systematically improved. Both photo- and electroluminescence (PL and EL) quantum efficienci...

Charge Accumulation Spectroscopy for Investigating Organic Photovoltaic Stability

In order to better understand the degradation mechanisms of inverted organic photovoltaics (OPV), a recently developed spectroscopic technique, charge accumulation spectroscopy, is applied. First, the application of this high‐resolution optical spectroscopy technique to OPV devices is demonstrated by detecting the polaronic absorption in a PTB7 (polythienothiophene derivative):PC70BM inverted OPV device and then the technique is used to investigate in situ device operational stability. The device instabilities are identified under operational conditions in vacuum leading to significant losses in open‐circuit voltage and fill factor (20% and 10%, respectively, after 80 h of white‐light exposure in vacuum), which are correlated to an interfacial charge‐transfer mechanism between the metal oxide and photoactive layers. It is suggested that under these conditions 0.2% of the PC70BM molecules become anions due to charge transfer from a highly doped ZnSrO layer leading to device degradation due to enhanced trap‐assisted recombination.

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.

Plasmon-induced slow aging of exciton generation and dissociation for stable organic solar cells

Fast degradation is a major issue with organic photovoltaics (OPVs). Integrating plasmonics with OPVs has improved their efficiency; however, the stability effects are unknown. We demonstrate that plasmonic effects can improve the lifetime and efficiency. The aging effects on charge carrier generation and transport are investigated. Confocal time-resolved photoluminescence of Au nanoparticle (NP) doped polymer blend was performed to understand the plasmonic effects on excited-state dynamics. Hot exciton generation is observed directly at the Au-NP surface, which contributed to achieving a nearly perfect exciton dissociation yield. We found that slow aging of the plasmonic effect and the hot exciton contribution are the reasons for the improved lifetimes of plasmon-enhanced OPVs. This work opens up a new direction for improving the stability of OPVs and enhancing the application of plasmonics.

Improving thermal stability of organic photovoltaics via constructing interdiffused bilayer of polymer/fullerene

Abstract The thermal stability of organic photovoltaics (OPVs) is greatly enhanced by using an interdiffused polymer/fullerene bilayer (ID-BL) as a photoactive layer. The solutions of poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl] (PCDTBT) and phenyl-C 71 -butyric-acid-methyl ester (PCBM) are sequentially deposited to form the ID-BL. For comparison, a single photoactive layer consisting of mixed domains of PCDTBT and PCBM (MX-SL) is prepared by depositing blended solution of PCDTBT and PCBM, which is the most widely used method for fabricating OPVs. After applying thermal stress at 80 °C for 10 days, the OPV utilizing the ID-BL photoactive layer maintained 97.2% of its initial efficiency, whereas the efficiency of the OPV utilizing the MX-SL photoactive layer decreased to 37.5% of its initial efficiency. The glazing angle X-ray diffraction (GIXRD) and Flory-Huggins interaction parameter analysis reveal that the ordered domain size of PCDTBT in ID-BL is greater than that of the MX-SL and the ordered domain is maintained after the thermal stress test. These findings imply that mixing of the PCDTBT and PCBM domains does not occur due to the enhanced ordering of PCDTBT in ID-BL during the thermal stress test. Meanwhile, the domain size of PCDTBT in MX-SL is reduced due to further mixing of the PCDTBT and PCBM domains during the thermal stress test, which deteriorates the optimized bulk heterojunction (BHJ) morphology. These results show that efficient and thermally stable OPVs can be realized by utilizing the ID-BL photoactive layer prepared by the sequential solution deposition.

Baselines for Lifetime of Organic Solar Cells

The process of accurately gauging lifetime improvements in organic photovoltaics (OPVs) or other similar emerging technologies, such as perovskites solar cells is still a major challenge. The presented work is part of a larger effort of developing a worldwide database of lifetimes that can help establishing reference baselines of stability performance for OPVs and other emerging PV technologies, which can then be utilized for pass‐fail testing standards and predicting tools. The study constitutes scanning of literature articles related to stability data of OPVs, reported until mid‐2015 and collecting the reported data into a database. A generic lifetime marker is utilized for rating the stability of various reported devices. The collected data is combined with an earlier developed and reported database, which was based on articles reported until mid‐2013. The extended database is utilized for establishing the baselines of lifetime for OPVs tested under different conditions. The work also provides the recent progress in stability of unencapsulated OPVs with different architectures, as well as presents the updated diagram of the reported record lifetimes of OPVs. The presented work is another step forward towards the development of pass‐fail testing standards and lifetime prediction tools for emerging PV technologies.