Photovoltaic Polymers Research Articles

Carbazole side-chained benzodithiophene based two-dimensional D-A conjugated photovoltaic polymers

In this work, one novel carbazole side chained benzodithiophene (BDT) monomer is designed and synthesized, and this new donor monomer based two D−A conjugated polymers with electron-withdrawing acceptor 4,7-di(4-(2-ethylhexyl)-2-thienyl)-5,6-difluoro-2,1,3-benzothiadiazole (DTffBT) (P5) and benzodithiophene-4,8-dione (BDD) (P7) are prepared. The polymers show 1.65–1.85 eV band gap, which is similar to the polymer with same backbone. The P5 based polymer solar cells show acceptable PCE around 8% and low enegy loss around 0.7 eV, which is similar to the fluorene side-chained polymer. P7 based polymer shows 1 V open-circuit voltage in both fullerene based and fullerene-free polymer solar cells. Molecular conformations, photophysical/electrochemical properties and film morphology of the device active layer blend films were also systematically investigated to reveal the structure−property relationships. This work suggests that carbazole unit is a promising π-conjugated side chain group for BDT monomer to construct efficient two-dimensional (2D) D−A conjugated photovoltaic polymers.

A Wide-Bandgap Conjugated Polymer Based on Quinoxalino[6,5-f ]quinoxaline for Fullerene and Non-Fullerene Polymer Solar Cells.

A wide-bandgap conjugated polymer, PNQx-2F2T, based on a ring-fused unit of quinoxalino[6,5-f ]quinoxaline (NQx), is synthesized for use as electron donor in polymer solar cells (PSCs). The polymer shows intense light absorption in the range from 300 to 740 nm and favorable energy levels of frontier molecular orbitals. The polymer has afforded decent device performance when blended with either fullerene-based acceptor [6,6]-phenyl-C71 -butylric acid methyl ester ([70]PCBM) or non-fullerene acceptor 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone-methyl))-5,5,11,11-tetrakis(4-n-hexylphenyl)-dithieno[2,3-d: 2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene (IT-M). The highest PCEs of 7.9% and 7.5% have been achieved for [70]PCBM or IT-M based PSCs, respectively. Moreover, the influence of molecular weight of PNQx-2F2T on solar cell performance has been investigated. It is found that fullerene-based devices prefer higher polymer molecular weight, while non-fullerene devices are not susceptible to the molecular weight of PNQx-2F2T. The device results are extensively explained by electrical and morphological characterizations. This work not only evidences the potential of NQx for constructing high-performance photovoltaic polymers but also demonstrates a useful structure-performance relationship for efficiency enhancement of non-fullerene PSCs via the development of new conjugated polymers.

Implication of side-chain fluorination on electronic properties, ordering structures, and photovoltaic performance in asymmetric-indenothiophene-based semiconducting polymers

Side-chain fluorination of conjugated polymers has been proved to be a highly effective approach for optimizing optical and electrical properties of the relative polymers. However, current studies on the fluorination are all based on symmetric molecular structures. In this work, two new D-A type photovoltaic polymers, namely PIT Ph -DT ff BT and PIT Phf -DT ff BT, based on asymmetric indenothiophene (IT) donor units with alkoxyphenyl or fluoroalkoxyphenyl substituents were designed and synthesized. Effects of the fluorine substitution in the asymmetric IT donor units on the electronic structure, ordering structure, photovoltaic properties, and charge generation and recombination dynamics were investigated. It is found that side-chain fluorination in the asymmetric donor units of the D-A polymers endowed the relative polymer with a deeper HOMO level, higher and more balanced charge mobilites, increased charge dissociation efficiency and reduced bimolecular recombination. As a result, the bulk heterojunction solar cell based on the blend film of PIT Phf -DT ff BT and PC 71 BM demonstrated an efficiency of 7.03%, whereas the cell efficiency based on PIT Ph -DT ff BT was only 5.68%. These results indicate that our design strategy by introducing a fluoroalkoxyphenyl unit as side chain to fabricate asymmetric IT-based polymer is efficient in improving the photovoltaic performance. We believe that the results provide new insights into the design of high-performance semiconducting photovoltaic polymers. • Two new D-A type asymmetric-indenothiophene-based polymers, PIT Ph -DT ff BT and PIT Phf -DT ff BT were obtained. • Side-chain fluorination in the asymmetric donor units has a remarkably positive impact. • PIT Phf -DT ff BT shows enhanced charge mobility, better crystallinity and surface morphology.

Impact of linker positions for thieno[3,2-b]thiophene in wide band gap benzo[1,2-b:4,5-b′]dithiophene-based photovoltaic polymers

Abstract

A New Method for the Synthesis of Bromine-Containing Heterocyclic Compounds for Photovoltaic Polymers

With the development and improvement of systems for converting sunlight into electric and thermal energy, more and more work is emerging on the development of the newest and most promising direction in solar energy, namely the creation of solar cells based on photosensitive polymers. Recently the power conversion efficiency of organic photovoltaic (OPV) devices has overcome the barrier of 17%, and thus we can expect a new wave of scientific interest in the development of new, more efficient OPV devices. Unfortunately, during searching for highly efficient chemical structures of OPV polymers, the researchers missed an important point: all photovoltaic polymers consist of aromatic and heteroaromatic «building blocks», which, in turn, are synthesized based on outdated techniques using highly toxic, dangerous for life and environment precursors. The development of «green», environmentally friendly, economically viable methods for the synthesis of photovoltaic polymers and building blocks for their production, will make the energy obtained from OPV truly «green». In this work, we present an alternative, «green» method for synthesizing halogen-containing aromatic and heteroaromatic, expensive building blocks most commonly used in the synthesis of photovoltaic polymers, which can be used to obtain photovoltaic polymers of various structures. We present the original methods for the synthesis of 4,4-dibromo-1,1- biphenyl (1), 4,7-dibromo-2,1,3-benzothiadiazole (2), 2-bromothiophene (3) and 2,5-dibromothiophene (4). All these methods differ from the previously described routes by their simplicity and convenience of their implementation, the absence of corrosive and irritant reagents, good yield and compliance with the principles of «Green Chemistry».

Conductive carbon nanosheets prepared from brominated polystyrene through ion beam irradiation and carbonization

We fabricated a conductive carbon nanosheet (CNS) film converted from brominated polystyrene (PS) and demonstrated that the CNS film can act as transparent electrode (TE) for polymeric photovoltaics (PPVs). The PS-converted CNS film was fabricated simply with spin-coating of a cost-effective PS solution, followed by stabilization via ion-beam irradiation and carbonization via heat treatment to convert PS to CNS. The analytical results revealed that the PS film was successfully stabilized by ion-beam irradiation and the conductive CNS with graphene-like structure was synthesized. The PPVs with the PS-converted CNS as a TE showed a feasible power conversion efficiency of ~0.61% under a standard 1 sun condition, thus, confirming that the ion-beam based CNS-formation approach and the PS-converted CNS can be useful in transparent electrode applications.

Fine-tuning head-to-head bithiophene-difluorobenzothiadiazole polymers for photovoltaics via side-chain engineering

Abstract High-performance polymer semiconductors generally should have wide absorption, good solution process-ability, and fine-tuned physicochemical properties in order to achieve satisfying photovoltaic performance. Herein, two new alkynyl-functionalized electron donor units, 3-alkyl-3′-alkynyl-2,2′-bithiophene (TRTRy) and 3-alkoxy-3′-alkynyl-2,2′-bithiophene (TORTRy), were invented through the combination of the alkynyl side chain with the alkyl or alkoxy side chain, respectively. Copolymerization of these bithiophenes with difluorobenzothiadiazole (ffBT) afforded polymers ffBT-TRTRy and ffBT-TORTRy, respectively. When applied into polymer solar cells (PSCs), devices using ffBT-TRTRy donor polymer display a maximum power conversion efficiency (PCE) of 2.34% with a short-circuit current (Jsc) of 7.46 mA cm−2, an open circuit voltage (Voc) of 0.93 V, and a fill factor (FF) of 34.0%. The TORTRy containing polymer ffBT-TORTRy affords PSCs with a much improved PCE of 6.60% with a higher Jsc of 15.09 mA cm−2, a larger FF of 58.3%, and a Voc of 0.75 V. The performance improvement of PSC devices using ffBT-TORTRy donor is mainly attributed to the simultaneous realization of higher Jsc and FF, while maintaining a good Voc. The results demonstrate that alkynyl-functionalized H-H bithiophenes are promising building blocks for efficient PSCs.

Theoretical study on organic dyes with tunable π-spacers for dye-sensitized solar cells: Inspired by the organic polymer photovoltaics

We present the theoretical investigation on tuning π-spacers in D-π-A organic dyes for dye-sensitized solar cells (DSSCs). The validity of three series of conjugate units (12 types) conventionally used in polymer photovoltaics are utilized as the π-spacers of organic dyes. Our results indicate that the extension of π conjugation can efficiently improve the absorption intensity. The absorption spectra red-shifts is because the increased π-spacers significantly destabilize the highest occupied molecular orbital level, whereas the lowest unoccupied molecular orbital level has negligible changed. Our simulation is expected to assist the design high performance dyes for dye-sensitized solar cells applications.

Side-chain effect in ethenylene fused thiophene-vinylene-thiophene (ETVT) based photovoltaic polymers

To investigate side chain effect of ETVT based photovoltaic polymers, we designed and synthesized the polymers with different solubilizing substituents. The impact of side chains on the solubility, planarity, optical and electronic properties of these ETVT based conjugated polymers was systematically studied. Extending the intrinsic alkyl group or adding new alkyl substituent to the polymer obviously increased the solubility of the resulting polymers. Thus, the polymerization reaction yield was improved to 88% and 81%, for PETVT-TBT24 and PETVT8-TBT, compared to that of 39% for PETVT-TBT. PETVT8-TBT showed blue-shifted absorption spectrum, reduced hole mobility and consequently inferior photovoltaic performance, owing to the steric hindrance caused by redundant octyl group on ETVT unit. However, the introduction of alkyl substitutes in ETVT remarkably increases the open-circuit voltage of PETVT8-TBT based PSCs to 1.03 V, by both decreasing HOMO of the polymer and reducing the energy losses. Extending the intrinsic alkyl group resolved the problem of low solubility of PETVT-TBT, and furthermore, was benefit to improve charge carrier mobility in the resulting polymer based solar cells. As a result, PETVT-TBT24 basically maintained the advantages of ETVT based photovoltaic polymers, realizing a moderate PCE of 7.8% when paired with the non-fullerene acceptor of ITIC.

Changing the π-bridge from thiophene to thieno[3,2-b]thiophene for the D-π-A type polymer enables high performance fullerene-free organic solar cells.

For photovoltaic polymers with a D-π-A backbone, there are a great deal of D and A units, but the choice of π bridge is relatively limited and thiophene (T) is still the most effective one. Here, we utilize two D-π-A polymers, J52-FS with thiophene as the π bridge and PE2 with thieno[3,2-b]thiophene (TT) as the π bridge, to combine with a low band-gap non-fullenere Y6, respectively. The photovoltaic cells based on PE2:Y6 can realize a PCE of 13.50%, which is obviously higher than the 10.58% PCE of the J52-FS:Y6 analogue. Our work demonstrates that using TT as the π-bridge is a simple and promising approach to construct efficient photovoltaic polymers.

How charges separate: correlating disorder, free energy, and open-circuit voltage in organic photovoltaics.

In order for a photovoltaic cell to function, charge carriers produced by photoexcitation must fully dissociate and overcome their mutual Coulomb attraction to form free polarons. This becomes problematic in organic systems in which the low dielectric constant of the material portends a long separation distance between independent polaron pairs. In this paper, we discuss our recent efforts to correlate the role of density of states, entropy, and configurational and energetic disorder to the open-circuit voltage, VOC, of model type-II organic polymer photovoltaics. By comparing the results of a fully interacting lattice model to those predicted by a Wigner-Weisskopf type model we find that energetic disorder does play a significant role in determining the VOC; however, mobility perpendicular to the interface plays the deciding role in the eventual fate of a charge-separated pair.

Plasmon-mediated nonradiative energy transfer from a conjugated polymer to a plane of graphene-nanodot-supported silver nanoparticles: an insight into characteristic distance.

Hybrid nanostructures comprising conjugated polymers (CPs) and plasmonic metals show excellent performance in light harvesting. However, the energy transfer mechanism of the CP film to nearby metal nanoparticles, especially knowledge of the characteristic distance, is still unclear. Here, quenching of the emission of a CP film in proximity to a monolayer of graphene-nanodot-supported silver nanoparticles (GND-Ag NPs) is investigated. Uniform Ag NPs with D = 3.2 nm were grown on GNDs in situ under mild light irradiation, and a series of bilayer structures of GND-Ag NPs/CPs were constructed by spin-coating blue, green and red light-emitting poly(9,9-dioctylfluorene) (PFO), poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) and poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV),respectively, on top of the GND-Ag NP plane. The spacer distance was controlled by the layers of assembled polyelectrolytes. Both steady and transient photoluminescence (PL) spectra showed emission quenching of the bilayer structures, providing the maximum efficiency of 99% for the F8BT films. The surface density of GND-Ag NPs and the spacer distance-dependent PL quenching data were analyzed within the plasmonic resonant energy transfer model, and the extracted characteristic distances are 6 nm, 3 nm and 10 nm for the PFO, F8BT and MEH-PPV systems, respectively. Current-sensing atomic force microscopy shows that the GND-Ag NPs/F8BT film exhibits enhanced electrical conductivity. These results are believed to be important for the development of plasmonic enhanced polymer photovoltaics and photocatalysis.

Steady Enhancement in Photovoltaic Properties of Fluorine Functionalized Quinoxaline-Based Narrow Bandgap Polymer.

To investigate the influence of fluoride phenyl side-chains onto a quinoxaline (Qx) unit on the photovoltaic performance of the narrow bandgap (NBG) photovoltaic polymers, herein, two novel NBG copolymers, PBDTT-DTQx and PBDTT-DTmFQx, were synthesized and characterized. 2-ethylhexylthiothiophene-substituted benzodithiophene (BDTT), 2,3-diphenylquinoxaline (DQx) [or 2,3-bis(3-fluorophenyl)quinoxaline (DmFQx)] and 2-ethylhexylthiophene (T) were used as the electron donor (D) unit, electron-withdrawing acceptor (A) unit and π-bridge, respectively. Compared to non-fluorine substituted PBDTT-DTQx, fluoride PBDTT-DTmFQx exhibited a wide UV-Vis absorption spectrum and high hole mobility. An enhanced short-circuit current (Jsc) and fill factor (FF) simultaneously gave rise to favorable efficiencies in the polymer/PC71BM-based polymer solar cells (PSCs). Under the illumination of AM 1.5G (100 mW cm−2), a maximum power conversion efficiency (PCE) of 6.40% was achieved with an open-circuit voltage (Voc) of 0.87 V, a Jsc of 12.0 mA cm−2 and a FF of 61.45% in PBDTT-DTmFQx/PC71BM-based PSCs, while PBDTT-DTQx-based devices also exhibited a PCE of 5.43%. The excellent results obtained demonstrate that PBDTT-DTmFQx by fluorine atom engineering could be a promising candidate for organic photovoltaics.

Enhanced Photovoltaic Performance in D-π-A Copolymers Containing Triisopropylsilylethynyl-Substituted Dithienobenzodithiophene by Modulating the Electron-Deficient Units.

Three alternated D-π-A type 5,10-bis(triisopropylsilylethynyl)dithieno[2,3-d:2′,3′-d′]-benzo[1,2-b:4,5-b′]dithiophene (DTBDT-TIPS)-based semiconducting conjugated copolymers (CPs), PDTBDT-TIPS-DTBT-OD, PDTBDT-TIPS-DTFBT-OD, and PDTBDT-TIPS-DTNT-OD, bearing different A units, including benzothiadiazole (BT), 5,6-difluorinated-BT (FBT) and naphtho[1,2-c:5,6-c′]-bis[1,2,5]thiadiazole (NT), were designed and synthesized to investigate the impact of the variation in electron-deficient units on the properties of these photovoltaic polymers. It was exhibited that the down-shifted highest occupied molecular orbital energy level (EHOMO), the enhanced aggregation in both the chlorobenzene solution and the solid film, as well as the better molecular planarity, were achieved using methods involving fluorination and the replacement of BT with NT on the polymer backbone. The absorption profile was little changed upon fluorination; however, it was greatly broadened during replacement of BT with NT. Consequently, the optimized photovoltaic device based on the PDTBDT-TIPS-DTNT-OD exhibited synchronous enhancements in the open-circuit voltage (VOC) of 0.88 V, the short-circuit current density (JSC) of 7.21 mA cm−2, and the fill factor (FF) of 52.99%, resulting in a drastic elevation in the PCE by 129% to 3.37% compared to that of the PDTBDT-TIPS-DTBT-OD. This was triggered by PDTBDT-TIPS-DTNT-OD’s broadened absorption, deepened EHOMO, improved coplanarity, and enhanced SCLC mobility (which increased 3.9 times), as well as a favorable morphology of the active layer. Unfortunately, the corresponding PCE deteriorated after incorporating fluorine into the BT, due to the oversized aggregation and large phase separation morphology in the blend films, severely impairing its JSC. Our preliminary results demonstrated that the replacement of BT with NT in a D-π-A type polymer backbone was an effective strategy of tuning the molecular structure to achieve highly efficient polymer solar cells (PSCs).

Angular/linear-shaped indacenodithiophene (IDT) for donor-acceptor copolymers: Geometric shape effects on physical properties and photovoltaic performance

Angular-indacenodithiophene (a-IDT) as the analogue of linear-IDT (l-IDT), in which the central phenyl ring was linked on the β-position of the thiophene ring but fused on its α-position, was designed and synthesized through intramolecular annulation. This designed dibrominated a-IDT monomer was copolymerized with 4,7-bis(4-hexylthiophen-2-yl)-2,1,3-benzothiadiazole (DTBT) as the acceptor unit through Stille coupling reaction to furnish an alternating D-A conjugated polymer Pa-IDTDTBT. Similarly, l-IDT unit and its D-A conjugated polymer Pl-DTDTBT were also synthesized for comparison. The geometric shape of l-IDT and a-IDT subunits have tremendous influence on the conjugated backbone curvature for Pl-IDTDTBT and Pa-IDTDTBT, mainly reflects in changes observed in their photoelectric properties, hole mobilities, film morphology and photovoltaic performance. Theoretical calculation concludes that Pl-IDTDTBT possesses a more linear conjugated backbone and hence stronger intermolecular π–π interactions, leading to more red-shifted absorption spectra of Pl-IDTDTBT in the solution as well as the thin film relative to those of Pa-IDTDTBT. XRD measurements demonstrated that Pl-IDTDTBT has more ordered π-stacking than Pa-IDTDTBT counterpart as a result of the less curvature of the Pl-IDTDTBT conjugated backbone. BHJ PSCs device based on Pl-IDTDTBT/PC71BM achieved a PCE of 5.34%, is higher than Pa-IDTDTBT (3.64%). As expected, Pa-IDTDBT with the more conjugated backbone curvature showed a high Voc of 1.02 V owing to its deeper HOMO energy level (−5.47 eV) relative to Pl-IDTDTBT, which is one of the highest Voc values of IDT-based polymers. Our work demonstrates that the geometric shape of subunits should be considered in designing the novel photovoltaic polymers and other organic optoelectronic materials.

Smart photoactive soft materials for environmental cleaning and energy production through incorporation of nanophotocatalyst on polymers and textiles

Energy and environment are key issues for the sustainable development of human beings and are also the current and long‐term focuses of scientific research. New energy and environmental technologies in combination with polymer and textile science work to create many additional functions for conventional polymers and fabrics. Therefore, some novel technical polymers and textiles, such as photovoltaic and photocatalytic polymers and textiles, have begun to emerge. Generally, light‐activated chemicals, materials, or processes that are produced or enabled by light and the agent absorbing light starting a photochemical alteration in the system is nominated as photocatalyst. This review firstly introduces the different photoactive materials, their classifications, and degradation mechanism. Then, inorganic semiconductor nanoparticles were selected as the best candidate for the application in soft materials. Finally, a detailed study was provided on both preparations of photoactive soft materials using metal oxide semiconductors and their advantages and applications. This paper will be more helpful for the scientists working in the field of photoactive soft materials.

Electronic structure theory gives insights into the higher efficiency of the PTB electron-donor polymers for organic photovoltaics in comparison with prototypical P3HT.

The electron donor poly-thienothiophene-benzodithiophene (PTB) polymer series displays remarkable properties that lead to more efficient bulk heterojunction (BHJ) organic solar cells. In this work, the ground and four excited states (bright S 1 and dark S 2-S 4) of three different members of the PTBn (n = 1, 6, 7) series were studied and compared with the prototypical poly(3-hexylthiophene) (P3HT) donor polymer. Time-dependent density functional theory was employed to investigate oligomers of similar sizes (∼50 Å). Charge alternation electron accumulation and depletion regions of the four transitions are concentrated on the inner units, thereby favoring interaction with the electron acceptor in a BHJ. The bright S 1 transition energies of PTBn are about 0.2 eV lower as compared to P3HT, thereby allowing a better match of their levels with the typical C60-type acceptor moiety in a BHJ. Side chains play a minor role in the electronic spectrum (less than ∼0.1 eV). The most efficient PTB7 transfers more electronic charge from its electron-rich benzodithiophene subunit to its electron-deficient thieno[3,4-b] thiophene subunit as compared to PTB1 and PTB6. We show that the dipolar effect, a partial concentration of negative and positive charges on the different parts of the donor polymer that favors charge separation, is more pronounced in PTBn polymers and typically an order of magnitude larger as compared to P3HT. These effects are conspicuous for the most efficient polymer of the series, PTB7, with its fluorine substituent shown to play a crucial role.

5,6-Bis(9-(2-decyltetradecyl)-6-fluoro-9H-carbazol-3-yl)naphtho[2,1-b:3,4-b']dithiophene as a Promising Donor Structure for D–A Conjugated Copolymers with a Narrow Bandgap

A new carbazole-containing naphthodithiophene derivative—heteroaromatic compound 5,6- bis[9-(2-decyltetradecyl)-9H-carbazol-3-yl]naphtho[2,1-b:3,4-b']dithiophene (M1)—has been synthesized. The compound will be used by us as a weak donor structural block for fabricating narrow-bandgap D–A conjugated polymers. The composition and structure of M1 have been confirmed by elemental analysis data, IR spectroscopy, and 1H and 13C NMR. The synthesized compound has a low HOMO energy (–5.4 eV), which is favorable for a high open-circuit voltage. Monomer M1 can be used as a promising weak donor moiety in D–A conjugated polymers for solar photovoltaics.

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.

Sunshine through the Looking Glass

Semitransparent photovoltaics installed onto windows can generate power and regulate temperature in buildings and vehicles. In this issue of Joule, Lunt et al. show the potential for wide-bandgap metal halide perovskite materials in visibly transparent solar cells and Yip et al. demonstrate a new design to block infrared radiation in tinted polymer photovoltaics.