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In the advancement of organic photovoltaics (OPV) toward scale‐up production, how to mitigate the batch instability of electron‐donating polymers originated from varied molecular weights remains a great challenge. By taking into consideration the relationship between the molecular weight of electron‐donating polymers and the relevant critical concentration (c*) of the solution, herein it is demonstrated that the aggregation behavior of the electron‐donating polymers can be tailored through manipulating c* of the polymer solution. It is interesting to note that the excessive aggregation in low‐molecular‐weight fractions can be circumvented while the favorable mixing ratio can be identified. By preparing the binary bulk heterojunction film under c*‐defined conditions for mixed‐molecular‐weight polymers, a notable power conversion efficiency of 19.1% for binary devices is achieved. Of particular importance is that a linear interrelation can be established between the c* for the maximum PCE and c* for the low‐molecular‐weight fraction aggregation, validating those straightforward spectra measurements can accurately and rationally guide the molecular weight mixing of photovoltaic donor polymers, thereby fully harnessing the potent driving force and affinity inherent to the low‐molecular‐weight fractions. These findings offer a straightforward and logical framework for addressing batch variability in the large‐scale production of high‐performance OPV devices. [ABSTRACT FROM AUTHOR]

In this work, pseudo-bilayer planar heterojunction (PPHJ) all-polymer solar cells (APSCs) were constructed on the basis of the commonly used PY-IT and PM6 as the acceptor and donor, respectively. A nonfullerene small molecular acceptor (NF-SMA) BTP-eC9 was incorporated into the PY-IT layer as the solid additive in consideration of its similar building block to PY-IT. BTP-eC9 can serve as a photon capture reinforcer and morphology-regulating agent to realize more adequate photon capture, as well as a more orderly molecular arrangement for effective carrier transport. By incorporating 2 wt% BTP-eC9, the efficiency of PM6/PY-IT-based PPHJ-APSCs was boosted from 15.11% to 16.47%, accompanied by a synergistically enhanced short circuit current density (JSC, 23.36 vs. 24.08 mA cm−2) and fill factor (FF, 68.83% vs. 72.76%). In another all-polymer system, based on PBQx-TCl/PY-DT as the active layers, the efficiency could be boosted from 17.51% to 18.07%, enabled by the addition of 2 wt% L8-BO, which further verified the effectiveness of using an NF-SMA as a solid additive. This work demonstrates that incorporating an NF-SMA as a solid additive holds great potential for driving the development of PPHJ-APSCs. [ABSTRACT FROM AUTHOR]

The performance of organic solar cells is sensitive to the film thickness and the uniformity of the donor and acceptor distribution in the photoactive layer. Especially, in the quasi‐planar heterojunction fabricated by layer‐by‐layer process, the donor and acceptor materials may be non‐homogeneously distributed across the entire photoactive layer. Visualization of the spatial distributions of donor and acceptor components sheds light on the relationship between nanostructures and device performances. Based on the distinct infrared absorption characteristics of the organic donor and acceptor, a quasi‐monochromatic light transmittance (QMLT) technique is proposed to quantify the donor and/or acceptor thickness in the photoactive layer blend across the entire device area with nanometer precision. The variation in thickness of donor and acceptor can be clearly and separately revealed. Accordingly, the impacts of spin coating techniques (such as dynamic or static dispensing, and on‐center or off‐center spin coating), as well as solvent choices, on film morphology and device performance can be correlated by the noncontact, nondestructive, and convenient QMLT method. [ABSTRACT FROM AUTHOR]

Photoinduced intermolecular charge transfer (PICT) determines the voltage loss in bulk heterojunction (BHJ) organic photovoltaics (OPVs), and this voltage loss can be minimized by inducing efficient PICT, which requires energy‐state matching between the donor and acceptor at the BHJ interfaces. Thus, both geometrically and energetically accessible delocalized state matching at the hot energy level is crucial for achieving efficient PICT. In this study, an effective method for quantifying the hot state matching of OPVs was developed. The degree of energy‐state matching between the electron donor and acceptor at BHJ interfaces was quantified using a mismatching factor (MF) calculated from the modified optical density of the BHJ. Furthermore, the correlation between the open‐circuit voltage (Voc) of the OPV device and energy‐state matching at the BHJ interface was investigated using the calculated MF. The OPVs with small absolute MF values exhibited high Voc values. This result clearly indicates that the energy‐state matching between the donor and acceptor is crucial for achieving a high Voc in OPVs. Because the MF indicates the degree of energy‐state matching, which is a critical factor for suppressing energy loss, it can be used to estimate the Voc loss in OPVs. [ABSTRACT FROM AUTHOR]

In the past five years, significant advancements in the development of novel conjugated polymer donors (D) and non‐fullerene acceptors (A), such as small molecules, have substantially boosted the power conversion efficiency of bulk heterojunction (BHJ) organic photovoltaics (OPVs) devices to over 19%. Recently, in the pursuit of broader impact and heightened efficiency for OPVs, an alternative processing approach has emerged; this approach involves a sequential deposition (SD) technique or a layer‐by‐layer method, creating active layers with p–i–n structures (p and n stand for D and A region, respectively; i stands for BHJ region). Notably, this SD method is particularly effective in semitransparent organic photovoltaics (ST‐OPVs), despite the material requirements it entails. SD‐processing methods enable the creation of vertical multiple junctions and controllable D/A interfaces, facilitating exciton dissociation and charge transport through a well‐designed pseudo p–i–n structure. Furthermore, ST‐OPVs can be integrated into building‐incorporated photovoltaic modules, offering potential applications in greenhouses and agricultural modernization. This integration allows for the comprehensive utilization of solar spectrum energy. In this review, current literature is consolidated on new materials, such as conjugated polymers and non‐fullerene small molecules as electron‐donating and electron‐withdrawing materials, aimed at high‐efficiency OPVs and ST‐OPVs with BHJ‐ and p–i–n structured active layers, and perspectives are offered for future developments. [ABSTRACT FROM AUTHOR]

The research for efficient organic materials organized in bulk heterojunction (BHJ) thin films for organic photovoltaics (OPVs) has shown a significant breakthrough in the past decade. Desired structural organization can be attained through various strategies. In this regard, the current review highlights tuning of alkyl chains introduced on molecular structures of active materials. The recent wide literature is classified based on the introduction of alkyl chains on polymers and small molecules used as donor and acceptor materials. The design of these materials, the morphological aspects of the active layers, and the performances of the related photovoltaic cells are detailed. A comprehensive discussion on chemical structures of the different material families considered, their modification by alkyl chains of various natures, and the morphological aspects are reported and tabulated. [ABSTRACT FROM AUTHOR]

Nowadays, Y-shaped non-fullerene acceptors become increasingly important in organic photovoltaics (OPV). Their use in binary and ternary bulk heterojunction composites continuously pushes up the efficiency of OPV devices. However, the mechanism of OPV performance enhancement by the third component of a ternary composite is rarely understood. In the present work, pulse EPR technique was used to reveal the similarities and the differences of photoinduced charge separation process in binary PM6/Y6 and ternary PM6/Y6:Y-T composites, where PM6 is polymer donor, Y6 and Y-T are different non-fullerene acceptors. Out-of-phase electron spin echo signal was detected for both composites, which is the signature of the charge-transfer state (CT state) formed at the donor/acceptor interface upon exciton splitting. Nearly identical distribution of the distances between the electron and the hole constituting the CT state was obtained for these composites from the analysis of this signal. In both cases the average electron-hole distance was 3.5 nm. It implies that OPV efficiency increase with Y-T addition is not caused by the increased probability of CT state dissociation followed by free charge generation for PM6/Y6:Y-T composite. [ABSTRACT FROM AUTHOR]

Multifunctional integration of optoelectronic devices within a single photodiode is in high demand for next‐generation on‐chip multifunctional integration and Internet of Things applications. Owing to the rapidity of nucleation‐crystallization that is associated with the solution method, large trap state densities (Nt), and consequently, severe dark current densities, as well as recombination losses are generally induced, which are detrimental to the detectivity (D*) of organic photodetectors (OPDs) and to the open‐circuit voltage (VOC) of organic photovoltaics (OPVs). Herein, a versatile p‐i‐n heterojunction organic photodiode with optimized vertical phase distribution and rational solid‐state packing is fabricated via a layer‐by‐layer (LBL) deposition procedure entailing the introduction of a rylene‐fullerene hybrid as a morphological modulator. This precisely controlled photodiode displayed suppressed Nt (2.5 × 1016 cm−3), low‐lying Urbach energy Eu (23.2 meV), as well as synergistically reduced series resistance, dark current, and sub‐bandgap radiative/non‐radiative recombination losses. Consequently, this ternary‐pseudo‐bilayer‐type photodiode exhibits excellent dual‐function performance with an outstanding D* of 9.48 × 1011 Jones in self‐powered OPD mode and a surprisingly suppressed energy loss of 0.538 eV in OPV mode. This study provides important insights into the mechanism and effects of trap density and energy disorder suppression in solution‐processed multifunctional integrated photoelectric conversion diodes. [ABSTRACT FROM AUTHOR]

Crystallinity of π‐conjugated polymer donors as well as acceptors is a crucial factor for boosting the performance of organic photovoltaic (OPV) cells. However, in the state‐of‐the‐art OPVs based on nonfullerene acceptors (NFAs), π‐conjugated polymers with low crystallinity are typically used and provide high efficiencies. Here, π‐conjugated polymers, named PTzBT and PTzBTE based on thiazolothiazole (TzTz), having similar crystallinity but different aggregation properties are blended with a number of acceptor materials such as PC71BM, IT‐4F, Y6, and Y12 having different aggregation property. Interestingly, whereas PTzBTE with higher aggregation properties forms crystalline structures in the blends regardless of the acceptor material, PTzBT with lower aggregation properties exhibits crystalline structures only when blended with acceptors having higher aggregation properties. Notably, the crystalline order of the materials in the blend films is correlated closely with the OPV performance. This study proposes that the interplay between the polymer donor and acceptor will play a crucial role in determining the crystalline order in the bulk heterojunction systems and thereby high photovoltaic performance. [ABSTRACT FROM AUTHOR]

Understanding organic photovoltaic (OPV) work principles and the materials' optoelectronic properties is fundamental for developing novel heterojunction materials with the aim of improving power conversion efficiency (PCE) of organic solar cells. Here, in order to understand the PCE performance (>13%) of OPV device composed of the non-fullerene acceptor fusing naphtho[1,2-b:5,6-b′]dithiophene with two thieno[3,2-b]thiophene (IDCIC) and the polymer donor fluorobenzotriazole (FTAZ), with the aid of extensive quantum chemistry calculations, we investigated the geometries, molecular orbitals, excitations, electrostatic potentials, transferred charges and charge transfer distances of FTAZ, IDCIC and their complexes with face-on configurations, which was constructed as heterojunction interface model. The results indicate that, the prominent OPV performance of FTAZ:IDCIC heterojunction is caused by co-planarity between the donor and acceptor fragments in IDCIC, the the charge transfer (CT) and hybrid excitations of FTAZ and IDCIC, the complementary optical absorptions in visible region, and the large electrostatic potential difference between FTAZ and IDCIC. The electronic structures and excitations of FTAZ/IDCIC complexes suggest that exciton dissociation can fulfill through the decay of local excitation exciton in acceptor by means of hole transfer, which is quite different from the OPVs based on fullerenes acceptor. The rates of exciton dissociation, charge recombination and CT processes, which were evaluated by Marcus theory, support the efficient exciton dissociation that is also responsible for good photovoltaic performance. [ABSTRACT FROM AUTHOR]

A precise picture of the photophysics that determine the efficiency of nonfullerene acceptor (NFA) bulk heterojunction (BHJ) organic solar cells is still missing, yet needed to mitigate the remaining loss channels. Herein, charge carrier generation and recombination dynamics in blends of a novel wide‐bandgap germanium‐containing donor polymer, namely, PEHGeNDT‐BT, paired with either O‐IDTBR or O‐IDTBCN as NFA in BHJ solar cells are investigated by (ultrafast) transient spectroscopy and time‐delayed collection field (TDCF) experiments. Photovoltaic devices yield moderate power conversion efficiencies (PCEs) of 5.3% when using O‐IDTBCN as the acceptor, and only about 2% when using O‐IDTBR as the acceptor, the latter severely limited by its low photocurrent and moderate fill factor (FF) of ≈43%. Time‐resolved photoluminescence experiments reveal limited exciton quenching as one loss channel in O‐IDTBR‐based blends, accompanied by significant geminate recombination further reducing the photocurrent, while field‐dependent charge generation is identified as the origin of the low FF. Geminate recombination is less in the O‐IDTBCN blend and charge generation is field‐independent, leading to improved photocurrent and FF. Carrier drift‐diffusion simulations of the devices' current–voltage (J–V) characteristics confirm that the experimentally determined kinetic parameters and process yields can reproduce the measured J–V curves under steady‐state solar illumination. [ABSTRACT FROM AUTHOR]

Herein, we elucidate the photodegradation pathway of A‐D‐A‐type non‐fullerene acceptors for organic photovoltaics. Using IT‐4F as a benchmark example, we isolated the photoproducts and proved them isomers of IT‐4F formed by a 6‐e electrocyclic reaction between the dicyanomethylene unit and the thiophene ring, followed by a 1,5‐sigmatropic hydride shift. This photoisomerization was accelerated under inert conditions, as explained by DFT calculations predicting a triplet‐mediated reaction path (quenchable by oxygen). Adding controlled amounts of the photoproduct P1 to PM6:IT‐4F bulk heterojunction cells led to a progressive decrease in photocurrent and fill factor attributed to its poor absorption and charge transport properties. The reaction is a general photodegradation pathway for a series of A‐D‐A molecules with 1,1‐dicyanomethylene‐3‐indanone termini, and its rate varies with the structure of the donor and acceptor moiety. [ABSTRACT FROM AUTHOR]

The influence of N‐substituents on the photovoltaic properties of singly bay‐linked perylene diimides (diPDIs) was systematically investigated to understand the aromatic‐aliphatic balance, which is beneficial for achieving high device performance in organic photovoltaic (OPV) systems. The synthesis of various N‐substituted diPDIs was successfully achieved using a newly developed one‐step procedure, resulting in sufficiently high yields. Detailed investigations of seven variants of diPDIs demonstrated that the primary alkyl substituents, particularly the 2‐ethylhexyl group, induce the self‐organized growth of thin films with high crystallinity. This is beneficial for enhancing the device performance of bulk heterojunction (BHJ) systems. The results presented herein reveal the important roles of alkyl side chains as hydrophobic solubilizing auxiliaries or primary determinants in the control of the active layer nanomorphology. This offers a valuable guideline that is essential for developing high‐performance organic semiconductor materials for future practical applications. [ABSTRACT FROM AUTHOR]

Despite the remarkable progress achieved in recent years, organic photovoltaics (OPVs) still need work to approach the delicate balance between efficiency, stability, and cost. Herein, two fully non‐fused electron acceptors, PTB4F and PTB4Cl, are developed via a two‐step synthesis from single aromatic units. The introduction of a two‐dimensional chain and halogenated terminals for these non‐fused acceptors plays a synergistic role in optimizing their solid stacking and orientation, thus promoting an elongated exciton lifetime and fast charge‐transfer rate in bulk heterojunction blends. As a result, PTB4Cl, upon blending with PBDB‐TF polymer, has enabled single‐junction OPVs with power conversion efficiencies of 12.76 %, representing the highest values among the reported fully unfused electron acceptors so far. [ABSTRACT FROM AUTHOR]

All‐polymer solar cells lag behind the state‐of‐the‐art in small molecule nonfullerene acceptor (NFA) bulk heterojunction (BHJ) organic solar cells (OSCs) for reasons still unclear. Herein, the efficiency‐limiting processes in all‐polymer solar cells are investigated using blends of the common donor polymer PBDT‐TS1 with different acceptor polymers, namely P2TPD[2F]T and P2TPDBT[2F]T. Combining data from steady‐state optical spectroscopy and time‐resolved photoluminescence, transient absorption, and time‐delayed collection field experiments, provides not only a concise but also quantitative assessment of the losses due to limited photon absorption, geminate and nongeminate charge carrier recombination, field‐dependent charge generation, and inefficient carrier extraction. Although both systems exhibit a similar charge separation efficiency in the absence of external bias, charge separation is significantly enhanced in P2TPDBT[2F]T‐based blends when biased. Kinetic parameters obtained via pulsed laser spectroscopy are used to reproduce the experimentally measured device current–voltage (J–V) characteristics and indicate that low fill factors originate either from nongeminate recombination competing with charge extraction, or from a pronounced field dependence of charge generation, depending on the acceptor polymer. The methodology presented here is generic and can be used to quantify the loss processes in BHJ OSCs including both all‐polymer and small molecule NFA systems. [ABSTRACT FROM AUTHOR]

This report presents recent progress in computational modeling efforts on blend morphology of P3HT:PCBM-based bulk heterojunction (BHJ) thin-film organic solar cells (OSCs). Improving power conversion efficiency (PCE), developing cost-effective fabrication methods and designing suitable electron donor and acceptor materials have been the most critical issues related to organic solar cell research in the past decade. Mixtures of poly-(3-hexyl-thiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) as electron-donor and electron-acceptor materials, respectively, have been widely investigated over the past decade. Despite the advances in experimental techniques, like atomic force microscopy (AFM), transmission (TEM) and scanning (SEM) electron microscopy and electron tomography, acquiring three-dimensional (3D) nanoscale morphological information from BHJ devices is challenging due to poor contrast in electron microscopy techniques of organic materials. Atomistic simulations are able to provide insights into the dynamics of blend morphology of OSCs and overcome the experimental challenges. In addition, coarse-grained molecular dynamics (CGMD) simulation is able to simulate structures approaching experimental length scales and processing conditions. Here we discuss about the insights that have been gained from classical atomistic simulations with an emphasis on CGMD modeling techniques developed in recent years. Effect of solution processing conditions and thermal annealing process on the morphology and dynamics of BHJ devices are reviewed as well. Finally, the future scope of molecular modeling efforts to tackle current and anticipated challenges in organic photovoltaic technologies are suggested, with a goal to identify the opportunities that remain open to be addressed by atomistic computations of OSCs. [ABSTRACT FROM AUTHOR]

Poly(3‐alkylthiophene) (P3AT) has been a central focus of research on organic photovoltaics (OPVs) for well over a decade. Due to their controlled synthesis P3ATs have proven to be a vital model system for developing an understanding of the effects of polymer structure on optoelectronic properties and blend morphology in bulk heterojunction OPVs. Similar to their thiophene counterparts, selenophene and tellurophene can be polymerized in a controlled manner. As single atom substitution results in significant differences in absorption, charge transport and self‐assembly these model systems provide a unique opportunity to probe fundamental structure‐property relationships. In this account, we provide an overview of our work on copolymers of thiophene and selenophene and examine how the optoelectronic and morphological behavior of these materials can be strategically adjusted through polymer design. We also highlight recent developments on poly(3‐alkyltellurophene) and comment on its future in fundamental and applied studies. [ABSTRACT FROM AUTHOR]

A perspective on the operating principles of organic bulk heterojunction solar cells is outlined and used to suggest an alternative device configuration, employing two type II semiconductor heterojunctions in series. Guiding principles to the implementation of this configuration, called a double heterojunction, are summarized. Assuming an exciton binding energy of 0.3 eV or less, results in a maximum achievable power conversion efficiency of well over 25 %. Achieving a high efficiency organic double heterojunction requires a specific energy level alignment, charge separation in the absence of driving forces, high phase purity and excellent diode quality. Fully conjugated triblock polymers of the form [D1‐A1]‐[D1‐A2]‐[D2‐A2] appear to be a system that can fulfill these requirements. Going forward, the primary challenge is the identification and development of synthetically tractable materials which have the necessary properties. [ABSTRACT FROM AUTHOR]

Organic bulk heterojunction solar cells are promising candidates as future photovoltaic technologies for large‐scale and low‐cost energy production. It is, therefore, not surprising that research on the design and preparation of these types of organic photovoltaics has attracted a lot of attention since the last two decades, leading to constantly growing values of energy conversion and efficiency. Combined with the possibility of a large‐scale production via roll‐to‐roll printing techniques, bulk heterojunction solar cells enable the fabrication of conformable, light‐weight and flexible light‐harvesting devices for point‐of‐use applications. This perspective review will highlight the recent advances toward mechanically robust and intrinsically stretchable bulk heterojunction solar cells. Mechanically robust fullerene‐based and all‐polymer devices will be presented, as well as a comprehensive overview of the recent challenges and characterization techniques recently developed to overcome some of the challenges of this research area, which is still in its infancy. [ABSTRACT FROM AUTHOR]

Organic photovoltaic cells commonly use an active layer with a polycrystalline bulk heterojunction. However, for simplifying the fabrication process, it may be worthwhile to use an amorphous active layer to lessen the burden on processing to achieve optimal performance. While polymers can adopt amorphous phases, molecular glasses, small molecules that can readily form glassy phases and do not crystallize over time, offer an appealing alternative, being monodisperse species. Our group has developed a series of reactive molecular glasses that can be covalently bonded to chromophores to form glass‐forming adducts, and this strategy has been used to synthesize glass‐forming donor and acceptor materials. Herein, the results of devices incorporating these materials in either partially or fully amorphous active layers are summarized. Additionally, these molecular glasses can be used as ternary components in crystalline systems to enhance efficiency without perturbing the morphology. [ABSTRACT FROM AUTHOR]

The rapid emergence of organic (opto)electronics as a promising alternative to conventional (opto)electronics has been achieved through the design and development of novel π‐conjugated systems. Among various semiconducting structural platforms, 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) π‐systems have recently attracted attention for use in organic thin‐films transistors (OTFTs) and organic photovoltaics (OPVs). This Review article provides an overview of the developments in the past 10 years on the structural design and synthesis of BODIPY‐based organic semiconductors and their application in OTFT/OPV devices. The findings summarized and discussed here include the most recent breakthroughs in BODIPYs with record‐high charge carrier mobilities and power conversion efficiencies (PCEs). The most up‐to‐date design rationales and discussions providing a strong understanding of structure‐property‐function relationships in BODIPY‐based semiconductors are presented. Thus, this review is expected to inspire new research for future materials developments/applications in this family of molecules. Semiconducting π‐frameworks based on 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) have attracted significant attention for use in organic (opto)electronics. This Review article provides an overview of the developments in the past 10 years on the structural design and synthesis of BODIPY‐based organic semiconductors and on their OTFT/OPV device applications. The research findings summarized and discussed here include the most recent breakthroughs involving BODIPYs with record‐high charge carrier mobilities and power conversion efficiencies and provides a firm understanding of structure‐property‐function relationships. [ABSTRACT FROM AUTHOR]

Abstract: Solution‐processed organic single‐crystalline donor–acceptor heterojunctions (SCHJs) composed of N,N,N′,N′‐tetraphenylbenzidine (TPB) and phenyl‐C61‐butyric acid methyl ester ([60]PCBM) are successfully obtained, and fundamental studies on its charge transport properties are demonstrated, revealing the advantages of applying SCHJs in photovoltaic devices. The SCHJs exhibit a balanced high‐mobility ambipolar charge transport with both hole and electron mobility being more than one‐order magnitude higher than its thin‐film heterojunction (TFHJ) counterparts. The difference between single‐crystalline and TFHJs in charge transport mechanisms was revealed, and it is shown that SCHJs present a more favorable band‐like charge transport properties at room temperature. Organic photovoltaics fabricated on SCHJs present much higher current density and a 32‐times higher power conversion efficiencies than TFHJ devices. The present work, which outlines comprehensive advantages of SCHJs in charge transport properties, should accelerate the application of organic single crystals for high‐performance photovoltaics. [ABSTRACT FROM AUTHOR]

Two N-heteroacene small molecules, P2BT and P2B2 T, with 2,1,3-benzodiathiazole end-capped N-heteroacene unit as the central building block have been designed and synthesized for bulk-heterojunction solar cells. Single-junction devices based on P2B2 T:PC 71 BM have achieved an impressive power conversion efficiency of 7.16% without any special treatment, which is the record efficiency among the N-heteroacene-based photovoltaics. [ABSTRACT FROM AUTHOR]

Herein, we investigate the use of a triptycenyl‐phenazino-thiadiazole as an electron acceptor in solution-processed organic bulk-heterojunction solar cells. We characterize the optoelectronic properties of the acceptor molecule and examine its performance with three different donor polymers. We find that blends with PTB7 show the highest performance reaching a power conversion efficiency of 2.4%. Investigations of 1,8-diiodooctane (DIO) as an additive resulted in only a minor increase in performance (∼10%), suggesting that additives allow rather insignificant control over the blend microstructure. Using transient absorption spectroscopy we identify the loss mechanisms in the device and propose routes to enhance the performance further. [ABSTRACT FROM AUTHOR]

Abstract: Fullerene‐based acceptors have dominated organic solar cells for almost two decades. It is only within the last few years that alternative acceptors rival their dominance, introducing much more flexibility in the optoelectronic properties of these material blends. However, a fundamental physical understanding of the processes that drive charge separation at organic heterojunctions is still missing, but urgently needed to direct further material improvements. Here a combined experimental and theoretical approach is used to understand the intimate mechanisms by which molecular structure contributes to exciton dissociation, charge separation, and charge recombination at the donor–acceptor (D–A) interface. Model systems comprised of polythiophene‐based donor and rylene diimide‐based acceptor polymers are used and a detailed density functional theory (DFT) investigation is performed. The results point to the roles that geometric deformations and direct‐contact intermolecular polarization play in establishing a driving force (energy gradient) for the optoelectronic processes taking place at the interface. A substantial impact for this driving force is found to stem from polymer deformations at the interface, a finding that can clearly lead to new design approaches in the development of the next generation of conjugated polymers and small molecules. [ABSTRACT FROM AUTHOR]

Non-fullerene acceptors are now capable of being used in high efficiency bulk heterojunction (BHJ) donor-acceptor organic solar cells. Acceptors comprising single or multiple linked chromophores have been used. We have developed a new non-fullerene molecular acceptor as well as two non-polymeric macromolecular materials that contain four equivalents of a similar chromophore, but can adopt different spatial arrangements of the chromophores. We compare the effect of having single and multiple chromophores within a macromolecule on the charge generation processes in P3HT:non-fullerene acceptor BHJ films using Transient Absorption Spectroscopy (TAS) and Time Resolved Microwave Conductivity (TRMC) measurements. It was found from the TAS measurements that at low weight percent (5 wt%) the single chromophore formed more polarons than the acceptors in which chromophores were linked, due to it having a more even distribution within the film. At higher concentrations (50 wt%) the trend was reversed due to the single chromophore forming crystalline domains, which reduced the interface area with the P3HT donor. The TRMC measurements showed that more mobile carriers were formed in the macromolecular acceptors when used at low concentrations in the blend and, independent of concentration, mobile carriers had a longer lifetime when compared to films containing the molecular material, which we ascribe to the charges being able to sample more than one chromophore and thus reduce recombination events. [ABSTRACT FROM AUTHOR]

Abstract: Stability of bulk heterojunction films for organic solar cells is a critical factor for commercial viability. One method to stabilize these films is to include cleavable side chains, which reduce the solubility of the polymers when removed. In order to study the stabilizing effect of cleavable side chains, a series of random copolymers using isoindigo with 0, 10, 20, 50, and 100% thermally cleavable side chains based on the tert‐butyloxycarbonyl (t‐BOC) group are synthesized. The polymers show a distinct one‐step thermal cleavage of the side chains, with no separable dealkylation and decarboxylation steps. The thermal stability in film is studied with transmission electron microscopy and atomic force microscopy. The polymer with all t‐BOC side chains on isoindigo significantly improves thermal stability with regard to crystal growth and phase separation in film. These results suggest BOC‐substitution can be used for large scale processing to produce insoluble polymer films with a high degree of thermal stability. [ABSTRACT FROM AUTHOR]

Abstract: For the commercial development of organic photovoltaics (OPVs), laboratory‐scale OPV technology must be translated to large area modules. In particular, it is important to develop high‐efficiency polymers that can form thick (>100 nm) bulk heterojunction (BHJ) films over large areas with optimal morphologies for charge generation and transport. Here, D1‐A‐D2‐A random terpolymers composed of 2,2′‐bithiophene with various proportions of 5,6‐difluoro‐4,7‐bis(thiophen‐2‐yl)‐2,1,3‐benzothiadiazole and 5,6‐difluoro‐2,1,3‐benzothiadiazole (FBT) are synthesized. It is found that incorporating small proportions of FBT into the polymer not only conserves the high crystallinity and favorable face‐on orientation of the D‐A copolymer FBT‐Th4 but also improves the nanoscale phase separation of the BHJ film. Consequently, the random terpolymer PDT2fBT‐BT10 exhibits a much improved solar cell efficiency of 10.31% when compared to that of the copolymer FBT‐Th4 (8.62%). Moreover, due to this polymer's excellent processability and suppressed overaggregation, OPVs with 1 cm2 active area based on 351 nm thick PDT2fBT‐BT10 BHJs exhibit high photovoltaic performance of 9.42%, whereas rapid efficiency decreases arise for FBT‐Th4‐based OPVs for film thicknesses above 300 nm. It is demonstrated that this random terpolymer can be used in large area and thick BHJ OPVs, and guidelines for developing polymers that are suitable for large‐scale printing technologies are presented. [ABSTRACT FROM AUTHOR]

Four new azafullerene monoadducts (DPS-C59N, HDP-C59N, DBOP-C59N, DHOP-C59N) have been prepared and applied as electron acceptors in solution-processed bulk heterojunction solar cells. The four compounds were designed so that their solubility in organic solvents was maximized and that structure-property comparisons could be drawn with a previously synthesized azafullerene electron acceptor. With the photovoltaic devices that were prepared from the four azafullerenes and polymeric electron donor PTB7 we found that only one of the four new electron acceptors resulted in a power conversion efficiency that exceeded the one observed with a previously reported azafullerene monoadduct. Atomic force microscopy and electron mobility measurements suggest that azafullerenes bearing two alkyl chains lead to non-optimal film morphologies as well as electron mobilities and that future efforts should focus on single n-alkyl substitution. [ABSTRACT FROM AUTHOR]

Abstract: Despite the need of a reliable technology for solar energy harvesting, research on new materials for third generation photovoltaics is slowed down by the diffuse use of trial and error rather than rational material design approaches. The proposed study investigates the use of alternative strategies to material discovery inspired by drug design and molecular modeling. In particular, training set and test set (for validation purposes) comprising well‐known small molecule‐bulk heterojunction organic photovoltaics were built. Molecules were characterized by semiempirical calculated and 3D molecular interaction fields–based descriptors. Then partial least squares algorithm was applied to rationalize structure‐photovoltaic activity relationships, and coefficients were investigated to clarify contributions played by the different molecular properties to the final performance. In addition, a photovoltaic desirability function (PhotD) was also proposed as alternative and versatile novel tool for ranking potential candidates. The partial least squares model and PhotD function were both internally and externally validated demonstrating their ability in estimating new candidates performances. The proposed approach demonstrates that, in the context of computational materials science, chemometrics and molecular modeling tools could effectively boost the discovery of novel promising candidates for photovoltaic application. [ABSTRACT FROM AUTHOR]

A novel, asymmetric benzothiadiazole-core π-conjugated organic semiconducting chromophore (CF-BTz-ThR) containing an alkyl bithiophene donor and 3,5-bis (trifluoromethyl) benzene as acceptor unit was synthesized via Suzuki cross-coupling in a relatively cost-effective way. The synthesized chromophore was applied as an acceptor material in the solution-processed fabrication of bulk heterojunction (BHJ) organic photovoltaics (OPVs). The presence of terminal hexyl chain in CF-BTz-ThR induced its solubility in common organic solvents. The energy levels of CF-BTz-ThR were calculated as −5.22 eV and −3.19 eV for HOMO and LUMO, respectively. The fabricated devices attained power conversion efficiency (PCE) of ∼3.52% for CF-BTz-ThR: PC 61 BM (1:3, w/w) ratio with the short circuit current (J SC ) of ∼10.38 mA/cm 2 and the open-circuit voltage (V OC ) of ∼0.68 V. The reasonable J SC and V OC of the devices might be attributed to strong absorption and emission properties as well as the electrochemical properties due to the presence of strong electron-withdrawing benzothiadiazole as well as –CF 3 unit as electron-acceptor. [ABSTRACT FROM AUTHOR]

'Nonfullerene' acceptors are proving effective in bulk heterojunction (BHJ) solar cells when paired with selected polymer donors. However, the principles that guide the selection of adequate polymer donors for high-efficiency BHJ solar cells with nonfullerene acceptors remain a matter of some debate and, while polymer main-chain substitutions may have a direct influence on the donor-acceptor interplay, those effects should be examined and correlated with BHJ device performance patterns. This report examines a set of wide-bandgap polymer donor analogues composed of benzo[1,2- b:4,5- b′]dithiophene (BDT), and thienyl ([2H]T) or 3,4-difluorothiophene ([2F]T) motifs, and their BHJ device performance pattern with the nonfullerene acceptor 'ITIC'. Studies show that the fluorine- and ring-substituted derivative PBDT(T)[2F]T largely outperforms its other two polymer donor counterparts, reaching power conversion efficiencies as high as 9.8%. Combining several characterization techniques, the gradual device performance improvements observed on swapping PBDT[2H]T for PBDT[2F]T, and then for PBDT(T)[2F]T, are found to result from (i) notably improved charge generation and collection efficiencies (estimated as ≈60%, 80%, and 90%, respectively), and (ii) reduced geminate recombination (being suppressed from ≈30%, 25% to 10%) and bimolecular recombination (inferred from recombination rate constant comparisons). These examinations will have broader implications for further studies on the optimization of BHJ solar cell efficiencies with polymer donors and a wider range of nonfullerene acceptors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Single-layer organic photovoltaics (OPVs) without interlayers are demonstrated. • Ternary blends are doped by immersion in a phosphomolybdic acid (PMA) solution. • Trap density and recombination loss are reduced without morphological changes. • PMA-doped ternary OPVs show high performance under diverse irradiation conditions. The commercial viability of organic photovoltaics (OPVs) can be improved by simplifying their device geometry and easing fabrication complexity. Here, we demonstrate that solution-based p -type electrical doping of ternary bulk heterojunction (BHJ) films, which comprise 2 donor polymers and 1 fullerene acceptor (2D:1A), enables the realization of efficient single-layer OPVs. Systematic and detailed investigations of the optoelectronic characteristics of films with varying donor ratios, and their photovoltaic performance, demonstrate p -type electrical doping via post-process immersion into a 12-molybdophosphoric acid hydrate (PMA) solution, resulting in a reduced trap density and charge recombination without significantly changing the BHJ morphology. Furthermore, PMA doping of films comprising optimized ternary blend compositions and polyethylenimine enables the demonstration of single-layer OPVs with economic top electrode metals and a high level of performance under outdoor and indoor illumination conditions. These PMA-doped 2D:1A BHJ films are an attractive platform to reduce the efficiency-cost gap and accelerate the commercialization of OPVs for emerging applications. [ABSTRACT FROM AUTHOR]

The synthesis, characterization and preliminary evaluation of two thienoisoindigo ( TII ) based molecules as donor materials in air processed bulk heterojunction solar cells are reported herein. The latter were built by grafting TII dyes on two different π-conjugated central cores, namely the cyclopentadithiophene and the fluorene units. Once blended with fullerene derivatives, power conversion efficiencies approaching 3% were measured, ranking amongst the highest reported value for thienoisoindigo-based molecular materials. [ABSTRACT FROM AUTHOR]

The influence of solvent additives on the temperature behavior of both charge carrier transport and recombination kinetics in bulk heterojunction solar cells has been investigated by electric noise spectroscopy. The observed differences in charge carrier lifetime and mobility are attributed to a different film ordering and donor-acceptor phase segregation in the blend. The measured temperature dependence indicates that bimolecular recombination is the dominant loss mechanism in the active layer, affecting the device performance. Blend devices prepared with a high-boiling-point solvent additive show a decreased recombination rate at the donor-acceptor interface as compared to the ones prepared with the reference solvent. A clear correlation between the device performance and the morphological properties is discussed in terms of the temperature dependence of the mobility-lifetime product. [ABSTRACT FROM AUTHOR]

Energy offset ( EDA) from a number of donor/acceptor heterojunctions is measured using ultraviolet photoemission spectroscopy. It is found that substrate work functions have little impact on the energy level alignments at donor/acceptor heterojunctions. Planar-heterojunction organic photovoltaic cells are made to test the relationship between energy offset and open-circuit voltage ( VOC). VOC is found to increase linearly as a function of EDA. The VOC, however, takes a surprising turn at EDA = 1.5 eV and starts to decrease as a function of donor-acceptor energy levels. To explain this experimental observation, a theoretical model to quantify the relationship between VOC and EDA is developed. The proposed model well explains the experimental data and, in particular, the reverse trend of VOC on EDA. By grouping several material constants into one variable, a simple universal plot that well describes the experimental data for both planar-heterojunction and bulk-heterojunction cells is generated. [ABSTRACT FROM AUTHOR]

Solution-processed organic photocell is one of the most promising candidates for the permanent power source for wireless devices. Since the device is not necessarily to be placed outdoor, and indoor light is generally weaker than outdoor light by 2-3 orders of magnitude, the characterization of the photocell under low-light illumination is important for this purpose. In this study, bulk heterojunction photocells based on a low-energy gap polymer poly[[4,8-bis[5-(2-ethylhexyl)thiophene-2-yl]benzo[1,2-b:4,5-b [ABSTRACT FROM AUTHOR]

A major problem for the use of single-wall carbon nanotubes (SWCNTs) in electronic devices relates to their poor processability. Chemical modification inevitably introduces defects in the nanotube lattice, resulting in a loss of electronic properties. In this contest, we report on a supramolecular approach with the aim of increasing the dispersion of SWCNTs in solution and in organic semiconductor matrices by ensuring the optoelectronic properties. In particular, new pyrenyl derivatives of thiophene have been synthesized and used to improve the solubility of SWCNTs for electron transfer in thin film heterojunction with poly(3-hexylthiophene) (P3HT) as donor system. Photoinduced electron transfer to SWCNTs has been demonstrated and the effect of different alkyl spacers, between the pyrene unit and the thiophene moiety, has revealed to play a key role. Electron transfer has been maximized by the compound with a spacer coplanar with the pyrene moiety due to the reduced separation between P3HT and SWCNTs. [ABSTRACT FROM AUTHOR]

Over the last 5 years, research on the synthesis, device engineering, and device physics of solution-processed small molecule solar cells (SMSCs) has rapidly expanded. Improvements in molecular design and emergent device processing techniques have helped solution-processed SMSCs overcome earlier difficulties in controlling active layer morphology, such that many systems are now at-or approaching-10% power conversion efficiency. In this review, details of the highest performing blend systems are presented in order to identify key trends and provide perspective on current progress in the field. Among the best systems, a planarized molecular structure is prevalent, which can be achieved using large fused-ring moieties, intermolecular non-bonding interactions, and side chain engineering. To obtain efficient devices, the highest performing systems have been optimized through the careful combination of thermal and solvent annealing procedures. Even without additional processing, some systems have been able to obtain interconnected morphologies and efficient charge generation and charge transport. Ultimately, the design of more efficient materials also requires additional understanding of the device physics and loss mechanisms. After highlighting what is known to date on processes limiting device efficiency, an outlook on the most important challenges remaining to the field is provided. [ABSTRACT FROM AUTHOR]

Due to the short diffusion length of approximately 10 nm of an exciton in bulk heterojunction (BHJ) organic solar cells (OSCs) comprising electron donors and acceptors, a formation with well phase-separated nanomorphology in BHJ films has been one of the most important issues in achieving efficient charge separation and extraction in OSCs. By adding a small amount of a high boiling point solvent or molecules to a bulk heterojunction (BHJ) solution, processing additive techniques have recently begun to offer an attractive and efficient method for controlling the nanoscale BHJ morphology of state-of-the-art OSCs with power conversion efficiencies (PCEs) exceeding approximately 11%. However, it remains unknown whether the effect of processing additives can potentially pave the way for the ongoing development of various BHJ components and the commercialization of OSCs. Here, recent progress in understanding and developing the effects of processing additives on OSCs is highlighted. This overview suggests possible guidelines for a wide range of BHJ components with respect to morphological/structural evolution. Furthermore, the rational correlations among processing additives, BHJ components, and fabrication technologies and the performance of high-performance and low-cost OSCs are discussed along with future commercialization prospects. [ABSTRACT FROM AUTHOR]

Understanding charge separation and charge transport at a molecular level is crucial for improving the efficiency of organic photovoltaic (OPV) cells. Under illumination of Bulk Heterojunction (BHJ) blends of polymers and fullerenes, various paramagnetic species are formed including polymer and fullerene radicals, radical pairs, and photoexcited triplet states. Light-induced Electron Paramagnetic Resonance (EPR) spectroscopy is ideally suited to study these states in BHJ due to its selectivity in probing the paramagnetic intermediates. Advanced techniques like pulsed EPR and ENDOR spectroscopy allow the determination of hyperfine coupling tensors, while high-frequency EPR allows the EPR signals of the individual species to be resolved and their g-tensors to be determined. The magnetic resonance parameters of the various polymer donors reveal details about the delocalization of the positive polaron which is important for the efficient charge separation in BHJ systems. Time-resolved EPR can contribute to the study of the dynamics of charge separation, charge transfer and recombination in BHJ by probing the unique spectral signatures of charge transfer and triplet states. EPR also has the potential to allow characterization of intermediates and products of BHJ degradation. [ABSTRACT FROM AUTHOR]

The performance of organic solar cells is strongly dependent on the morphology of the bulk heterojunction active layer. There has been intense efforts to identify and quantify morphological traits that correlate with various stages of the photo physics. While it is generally accepted that donor domain size affects exciton dissociation efficiency and connectivity affects charge collection, identifying morphology trait(s) that correlate with fill factor and total efficiency have remained elusive. In this work, we utilize correlation analysis on a large set of two dimensional bulk heterojunction morphologies to identify traits that are correlated with fill factor and efficiency. A large dataset of bulk heterojunction morphologies using a phase-field model of phase separation was first created. A comprehensive suite of morphology descriptors were evaluated for each of these morphologies using a recently developed graph based approach. Following this, a morphology aware excitonic-drift-diffusion based device model was used to compute current-voltage curves, fill factors, efficiencies as well as spatial distributions of exciton generation, dissociation, and charge collection for each of the morphologies. We find that (for a given material system with a specified HOMO-LUMO gap, and assuming perfect contact with electrodes) device efficiency primarily depends on the short circuit current, and has almost no dependence on the fill factor. Interestingly, we find that the fill factor is largely insensitive to many of the investigated descriptors. It is only weakly dependent on the contact area mismatch – the difference between the fraction of anode in direct contact with donor and the fraction of cathode in direct contact with acceptor. The fill factor is maximized when this quantity is nearly balanced. Since morphologies with a higher fraction of the electrodes in contact with the desirable material show higher short circuit current, we conclude that designing morphologies for a high short circuit current will necessarily lead to reasonably high fill factors. [ABSTRACT FROM AUTHOR]

The efficiency of bulk heterojunction organic photovoltaic cells can be enhanced through heat treatment of the components of the blend solution. The morphology of films spun from the heat treated blend solution reveals a more favorable diffusion of [6,6]-phenyl-C61-butyric acid methyl ester into the Poly(3-hexylthiophene-2,5-diyl) matrix than observed in the separate heating of the individual solutions. Heat treatment of a Poly(3-hexylthiophene-2,5-diyl) solution showed an enhanced Raman intensity associated with structural ordering. Heating of the blend solution after pre-heating P3HT solution to form a bulk heterojunction (P3HT:PCBM) with a ratio of 1:1 leads to limited diffusion of the [6,6]-phenyl-C61-butyric acid methyl ester phase into the crystalline Poly(3-hexylthiophene-2,5-diyl) phase. This study showed that solution heat treatment of a P3HT:PCBM blend leads to structural ordering of the Poly(3-hexylthiophene-2,5-diyl) polymer which modified the optical, morphological, PL and Raman characteristics relative to highly ordered Poly(3-hexylthiophene-2,5-diyl). The high Poly(3-hexylthiophene-2,5-diyl) polymer crystallinity enhanced the red shifted optical absorption, narrowed the full width at half maximum of Raman peaks and decreased the photoluminescence intensity upon solution heat treatment. The efficiency of the Bulk heterojunction made from a solution heat treated blend has yielded maximum power conversion efficiency of 3.0% and a fill factor up to 43% under Air Mass 1.5, 100-mW/cm 2 illumination. Separate heat treatment of a Poly(3-hexylthiophene-2,5-diyl) solution before forming the blend did not improve the current-voltage properties of an organic photovoltaic device. Rather the simultaneous ordering of Poly(3-hexylthiophene-2,5-diyl) as well as the diffusion of [6,6]-phenyl-C61-butyric acid methyl ester into the Poly(3-hexylthiophene-2,5-diyl) was the main contributor to the enhanced device performance. We compare the short time heating of the blend solution to a standard reference device made from long time stirring of a blend at low temperature. [ABSTRACT FROM AUTHOR]

A combination of fast scanning chip calorimetry and X-ray ptychography is explored to study the effects of thermal annealing on the active layer of bulk heterojunction organic photovoltaics. The well-known P3HT/PC 61 BM 1:1 system is investigated as a test case. By using a custom chip calorimetry setup, it is possible to give a thermal treatment at 127 °C (400 K) to P3HT/PC 61 BM 1:1 thin layers, using a heating and cooling rate of 30000 K s −1 , after which the resulting morphology is investigated with X-ray ptychography. Applying only heating and cooling, without isothermal annealing, yields a featureless morphology. This corresponds well with thermal data which indicate a mixed amorphous phase only. For increasing isothermal annealing times, a well-defined morphology appears with increasing domain size, corresponding to the formation of an endothermal melting trajectory. This melting trajectory is expected to consist of both eutectic melting and melting of coarsened crystals. In contrast to chip calorimetry results, large domain sizes are obtained for heating and cooling without isothermal annealing at a conventional rate of 20 K min −1 . This initial morphology then develops further with increased isothermal annealing. The combination of chip calorimetry and ptychography allows separating the effects of each single thermal step on morphology development. [ABSTRACT FROM AUTHOR]

Several carbazole-2,7-diyl units with alkoxy substituents at the 4-position in addition to branched (1-alkyl)alkyl substituents at the 9-position were developed and combined with difluorinated dithienylbenzothiadiazole by using a Suzuki coupling reaction to synthesize donor–π–acceptor-type copolymers. X-ray diffraction analyses of these copolymers revealed that the 4,9-disubstituted carbazole unit contributed to form a balanced interdigitated structure, which resulted in smaller π-stacking distances (4.0–3.5 Å) of the polymer backbone, a narrower bandgap (2.0–1.8 eV), and higher hole mobilities (4.2 × 10 −4 to 2.9 × 10 −3 cm 2 V −1 s −1 ) than those of the carbazole copolymer without the 4-substituent ( PCDT2FBT ). A bulk heterojunction organic photovoltaic device with a configuration of ITO/PEDOT:PSS/polymer:PC 70 BM/LiF/Al exhibited a power conversion efficiency of 5.46%, a short-circuit current density of 12.4 mA cm −2 , a fill factor of 0.58, and an open-circuit voltage of 0.76 V. The photovoltaic performance was much higher than that of PCDT2FBT . These results demonstrate that incorporation of the side chains into the 4,9-positions of carbazole is a novel approach to obtain self-organizing carbazole polymers, enabling improvement in light absorption, hole mobility, and photovoltaic performance. [ABSTRACT FROM AUTHOR]

The chemical structure of conjugated polymers plays an important role in determining their physical properties that, in turn, dictates their performance in photovoltaic devices. 5-Fluoro-2,1,3-benzothiadiazole, an asymmetric unit, is incorporated into a thiophene-based polymer backbone to generate a hole conducting polymers with controlled regioregularity. A high dipole moment is seen in regioregular polymers, which have a tighter interchain stacking that promotes the formation of a morphology in bulk heterojunction blends with improved power conversion efficiencies. Aliphatic side chain substitution is systematically varied to understand the influence of side chain length and symmetry on the morphology and resultant performance. This side chain modification is found to influence crystal orientation and the phase separated morphology. Using the asymmetric side chain substitution with regioregularity of the main chain, an optimized power conversion efficiency of 9.06% is achieved, with an open circuit voltage of 0.72 V, a short circuit current of 19.63 mA cm−2, and a fill factor over 65%. These results demonstrate that the local chemical environment can dramatically influence the physical properties of the resultant material. [ABSTRACT FROM AUTHOR]

An unconventional approach is applied for the first time to study the effect of silver nanoparticles incorporation in plasmonic organic photovoltaic devices. The incorporation of silver nanoparticles in the photoactive film results in enhanced PV performance and stability with respect to the reference device. The role of the local morphology in improving the plasmonic device properties is addressed by time-resolved high spatial resolution X-ray diffraction investigations. TR-HRXD was performed in-situ on an integrated OPV device incorporating silver nanoparticles in the photoactive layer during annealing (simulating the working conditions). Such time-space resolved method allowed tracking the modifications of the structural properties at each layer and interfaces. Remarkably, it is demonstrated that it possible to track the variation of the plasmonic spatial distribution inside the device over time, a factor strongly influencing the photovoltaic performance. [ABSTRACT FROM AUTHOR]