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Understanding excited-state reorganization energies, exciton diffusion lengths and non-radiative (NR) recombination, and the overall optoelectronic responses of nonfullerene small molecule acceptors (NF-SMAs) is important in order to rationally design new materials with controlled properties. While the effects of structural modifications on the optical gaps and electron affinities of NF-SMAs have been studied extensively, analyses of their absorption spectra that carefully characterize electronic and vibrational contributions that allow comparisons of reorganization energies and their implications for exciton diffusion lengths and NR recombination have yet to be reported. Here, we study the room temperature absorption spectra of three structural classes of NF-SMAs in dilute solutions through multiparameter Franck Condon (MFC) analyses and density functional theory (DFT) calculations. We show that the absorption spectra of these NF-SMAs can be categorized based on molecular structure-spectra correlation. The absorption spectra of curved, Y6-like structures can be described using an MFC model with two electronic transitions and two effective vibrational modes. The results of MFC/DFT analyses reveal that Y6 exhibits the smallest intra-molecular reorganization energy among the materials studied. Linear ITIC-like molecular structures reveal larger reorganization energies and reduced conformational uniformity compared to Y6. Meanwhile structures such as IDTBR and IEICO, which have an extra π-conjugated moiety between the donor and acceptor moieties, have large excited-state reorganization energies and low degrees of conformational uniformity. Since the intra-molecular reorganization energy is correlated with exciton diffusion length and nonradiative voltage losses (Δ

In organic solar cells (OSCs), a thick active layer usually yields a higher photocurrent with broader optical absorption than a thin active layer. In fact, a ∼300 nm thick active layer is more compatible with large-area processing methods and theoretically should be a better spot for efficiency optimization. However, the bottleneck of developing high-efficiency thick-film OSCs is the loss in fill factor (FF). The origin of the FF loss is not clearly understood, and there a direct method to identify photoactive materials for high-efficiency thick-film OSCs is lacking. Here, we demonstrate that the mobility field-dependent coefficient is an important parameter directly determining the FF loss in thick-film OSCs. Simulation results based on the drift-diffusion model reveal that a mobility field-dependent coefficient smaller than 10

This work integrates greenhouse energy demand, solar power production, and plant growth modeling to assess the economic opportunity of organic solar powered greenhouses. Results show these systems have positive economic outlook across broad climates.

Top and bottom surfaces of polymer films are used to construct interfaces in heterojunction based devices, affecting device figure of merit significantly with their different aggregation states.

It is revealed that the re-entrant phase behavior of the conjugated polymer:small molecule systems is indeed a result of thermodynamics. The composition difference (Δϕ) between liquidus and binodal reflects the crystalline–amorphous interaction.

A new unsymmetric small-molecule acceptor (SMA) BTPOSe-4F was designed by unsymmetric structure modification to Y6 with an alkyl upper side chain replaced by an alkoxy side chain and a sulfur atom in its central fused ring replaced by a selenium atom, for the application as an acceptor to fabricate organic solar cells (OSCs). BTPOSe-4F exhibits a higher lowest unoccupied molecular orbital (LUMO) energy level, a reduced nonradiation energy loss, and better charge extraction properties in its binary OSCs with a higher

Summary As the power conversion efficiency of organic photovoltaic has been dramatically improved to over 18%, achieving long-term stability is now crucial for applications of this promising photovoltaic technology. Among the high-efficiency systems, most are using BTP-4F and its analogs as acceptors. Herein, we determine the thermal transition temperatures (Tg) of seven BTP analogs to develop a structure-Tg framework. Our results point out an unresolved molecular design conundrum on how to simultaneously achieve high performance and intrinsic stability with BTP-based acceptors. We also show that PC71BM has miscibility above the percolation threshold in PM6 and can maintain local charge percolation and improved stability in ternary devices. However, PC71BM is not miscible with BTP-C3-4F and unfavorable vertical gradients that develop during aging still degrade performance. This points to a second thermodynamic conundrum. A compound with differential miscibility in the donor polymer can only impact percolation, and a compound with differential miscibility with the BTP only impacts diffusion.

Current non-fullerene organic photovoltaics (OPVs) can achieve high photocurrent generation yields with small donor/acceptor energy offsets. However, the effect of varying energy offset on the char...

Rapid increase in the power conversion efficiency of organic solar cells (OSCs) has been achieved with the development of non-fullerene small-molecule acceptors (NF-SMAs). Although the morphological stability of these NF-SMA devices critically affects their intrinsic lifetime, their fundamental intermolecular interactions and how they govern property–function relations and morphological stability of OSCs remain elusive. Here, we discover that the diffusion of an NF-SMA into the donor polymer exhibits Arrhenius behaviour and that the activation energy Ea scales linearly with the enthalpic interaction parameters χH between the polymer and the NF-SMA. Consequently, the thermodynamically most unstable, hypo-miscible systems (high χ) are the most kinetically stabilized. We relate the differences in Ea to measured and selectively simulated molecular self-interaction properties of the constituent materials and develop quantitative property–function relations that link thermal and mechanical characteristics of the NF-SMA and polymer to predict relative diffusion properties and thus morphological stability. Studies on the morphology stability of polymer donor–small-molecule acceptor blends relevant to solar cell stability reveal relationships between their intermolecular interactions and the thermodynamic, kinetic, thermal and mechanical properties.

Molecular innovation is highly important to achieve highly efficient small-molecule organic solar cells (SMOSCs). Herein, we report two small-molecule donors, namely, B3T-T and B3T-P, which differ only in their conjugated side chains: the former with a thienyl group and the latter with a phenyl unit. Surprisingly, both small-molecule donors show distinct electron density distribution and electrostatic potential along the conjugated backbone. B3T-P has a much higher dipole moment (0.920 D) than that of B3T-T (0.237 D). In SMOSCs, the B3T-T:BO-4Cl-based device shows a decent power conversion efficiency (PCE) of 11.1%. In contrast, the B3T-P:BO-4Cl-based device gives an outstanding PCE of 15.2%, which is one of the highest values among SMOSCs. Compared to the B3T-P-based device, although the B3T-T-based device has a large enough driving force for exciton separation and an extremely low non-radiative recombination voltage loss (0.168 V) for achieving high open-circuit voltage, the large domain size (63 nm) and low domain purity in the B3T-T:BO-4Cl-based device results in a relatively low short-circuit current density and fill factor, thus giving a low PCE. This result may pave the way to rationally design SM donors for highly efficient SMOSCs.

In developing organic semiconductor polymers for photovoltaic applications, chlorine substitution has become an effective strategy in replacing fluorine substitution to overcome the drawbacks of low yield and high cost, commonly associated with fluorination. In general, several molecular positions are available for chlorination. To obtain a clear understanding of the impact of chlorine substitution on the intrinsic polymer properties, an investigation of structure-property relationships is necessary. Herein, four donor-acceptor type polymers with the same conjugated backbone and flexible alkyl chains, but with chlorine atoms in different positions, are employed to systematically investigate the effect of the site of chlorination on the optoelectronic properties and photovoltaic performance. Substitution of fluorine by chlorine in the backbone slightly increases open circuit voltage (Voc) and fill factor (FF) of the solar cells but causes a loss of short-circuit current density (Jsc). The introduction of chlorine in the conjugated side chains, however, significantly improves Voc, FF, and power conversion efficiency, benefiting from a lower HOMO energy level, efficient and well-balanced transport properties, and superior nanoscale morphology. This journal is

The field of organic solar cells has experienced paradigm-shifting changes in recent years because of the emergence of nonfullerene acceptors (NFAs). It is critically important to gain more insight...

Combining the acceptor–donor–acceptor-type fused ring-based molecular architecture into a polymeric backbone is a promising strategy to design polymer acceptors for high-performance all-polymer sol...

Donor polymer number-average molar mass (Mn) has long been known to influence organic photovoltaic (OPV) performance via changes in both the polymer properties and the resulting bulk heterojunction...

With the recent remarkable advances in the efficiency of organic solar cells, the need to distill key structure–property relationships for semiconducting materials cannot be understated. The fundam...

Semitransparent organic photovoltaic cells (ST-OPVs) are emerging as a solution for solar energy harvesting on building facades, rooftops, and windows. However, the trade-off between power-conversion efficiency (PCE) and the average photopic transmission (APT) in color-neutral devices limits their utility as attractive, power-generating windows. A color-neutral ST-OPV is demonstrated by using a transparent indium tin oxide (ITO) anode along with a narrow energy gap nonfullerene acceptor near-infrared (NIR) absorbing cell and outcoupling (OC) coatings on the exit surface. The device exhibits PCE = 8.1 ± 0.3% and APT = 43.3 ± 1.2% that combine to achieve a light-utilization efficiency of LUE = 3.5 ± 0.1%. Commission Internationale d’eclairage chromaticity coordinates of (0.38, 0.39), a color-rendering index of 86, and a correlated color temperature of 4,143 K are obtained for simulated AM1.5 illumination transmitted through the cell. Using an ultrathin metal anode in place of ITO, we demonstrate a slightly green-tinted ST-OPV with PCE = 10.8 ± 0.5% and APT = 45.7 ± 2.1% yielding LUE = 5.0 ± 0.3% These results indicate that ST-OPVs can combine both efficiency and color neutrality in a single device.

Currently, high-performance organic solar cells (OSCs) are mainly composed of narrow band gap (NBG) nonfullerene acceptors and medium band gap (MBG) polymer donors, whereas the solar cells based on...

Summary Multi-component organic solar cells (OSCs) comprising more than two donor and acceptor materials have attracted significant research attention, as they can offer broader and better absorption, hence increasing solar cell performance. However, the morphology of multi-component OSCs is exceptionally complicated and challenging to control. Here, we develop a highly efficient (near 17.7%) quaternary OSC (q-OSC) using two polymer donors (namely PM6 and PTQ10) along with a fullerene (PC71BM) and a non-fullerene acceptor (N3). Our quaternary system demonstrates a new type of “rivers and streams” functional hierarchical (multi-length scale) morphology, where small domains of PTQ10 and PC71BM act as separators that spatially separate PM6 and N3, which effectively suppressed charge recombination, enhanced hole transport, and balanced charge transportation. These improvements in the quaternary system contribute to the increased internal quantum efficiency (IQE) and, thus, lead to an excellent JSC and device performance, which surpass their respective binary and ternary OSCs.

Conjugated polymers have proven to be an important class of materials for flexible and stretchable electronics. To ensure long-term thermal and mechanical stability of associated devices, there is ...

Summary Polythiophene (PT) and its derivatives have attracted long-standing attention in the organic photovoltaic community for their low cost and high scalability of synthesis. However, due to the lack of rational guidelines in controlling morphology and matching materials, the power conversion efficiencies (PCEs) based on PTs reported so far are generally below 10%. Here, we establish the first-ever relationship between miscibility, morphology, and device performance of binary blends, based on various nonfullerene acceptors (ITIC-Th1, ITIC, IT4F, IDIC, and Y6) and a PT derivative named PDCBT-Cl by scattering and calorimetric characterizations. Benefiting from a properly quenched mixed phase, PDCBT-Cl:ITIC-Th1 system shows the best efficiency of over 12%. Conversely, the blend of PDCBT-Cl and the star acceptor Y6 remained in a homogeneous state due to their high miscibility, resulting in abysmal performance with PCE of 0.5%. Specific guidelines are also proposed to remediate the performance of PDCBT-Cl:Y6, which are crucial for advancing their practical applications.

Summary Greenhouses vastly increase agricultural land-use efficiency. However, they also consume significantly more energy than conventional farming due in part to conditioning the greenhouse space. One way to mitigate the increase in energy consumption is to integrate solar modules onto the greenhouse structure. Semitransparent organic solar cells (OSCs) are particularly attractive given that their spectral absorption can be tuned to minimize the attenuation of sunlight over the plants photosynthetically active spectrum. Here, the benefits of integrating OSCs on the net energy demand of greenhouses within the U.S. are determined through a detailed energy balance model. We find that these systems can have an annual surplus of energy in warm and moderate climates. Furthermore, we show that sunlight reduction entering the greenhouse can be minimized with appropriate design. These results demonstrate that OSCs are an excellent candidate for implementing in greenhouses and provide an opportunity to diversify sustainable energy generation technology.

Y6-type non-fullerene acceptors (NFAs) with an acceptor–donor–acceptor′–donor–acceptor (A–D–A′–D–A) structure have been very popular in the field of organic solar cells (OSCs) due to their excellent performances. In this study, two novel NFAs, BTPS-4F and BTPS-4Cl were designed by incorporating undecylthio side chains into a thienothiophene moiety and connecting it to two different halogenated 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile end groups (2F-IC and 2Cl-IC) respectively. When blended with a donor polymer, PM6, BTPS-4F-based devices achieved a high power conversion efficiency (PCE) of up to 16.2% with an open-circuit voltage (VOC) of 0.82 V, a short-circuit current density (JSC) of 25.2 mA cm−2 and a fill factor (FF) of 0.78, while BTPS-4Cl-based devices achieved an inferior PCE of 13.5%. This is the first time alkylthio chains are employed on Y6-like NFAs to achieve high-performance OSCs. Subsequent characterization showed that the upshifted energy level of BTPS-4F and the better intermolecular packing in PM6:BTPS-4F blends are the major reasons for the enhanced performance of BTPS-4F-based devices over BTPS-4Cl-based ones. This work provides high-performance non-fullerene acceptors for OSCs and demonstrates a promising molecular design strategy that can effectively regulate their energy levels and morphology.

Power conversion efficiencies (PCEs) in organic solar cells (OSCs) have rapidly improved in the last 5 years owing largely to the development of novel small-molecule acceptors and polymer donors with several systems’ performances exceeding 17%. A key factor for these materials implementation into industrial relevant devices is their active layer thickness tolerance as solar cell performances are typically reported with thicknesses on the order of 100–150 nm, but thicker films (ca. 300 nm) are needed for printing and roll-to-roll processing. In this report, two PM7 isomeric derivatives were synthesized featuring a chlorinated benzodithiophene and ester functionalized terthiophene moieties for the incorporation into non-fullerene OSCs. The fundamental difference between the two isomeric polymers is the location of the ester side chains where the PM7 D1 esters are located on the outer thiophene units, whereas the esters on PM7 D2 are located on the central thiophene unit. This simple modification produced polymers with similar absorption profiles, electrochemical onsets, charge carrier mobilities when blended with ITIC-4F, and grazing-incidence wide-angle X-ray scattering patterns. Thin-film (100 nm) OSCs were fabricated resulting in average PCEs of 11.6% for PM7, 12.1% for PM7 D1, and 9.9% for PM7 D2 when blended with ITIC-4F. In contrast, large differences are observed in PCE when the active layer thickness is increased to 180 nm resulting in a decrease in average PCE for PM7 D2 (5.3%), whereas PM7 D1 was able to retain a 11.9% average PCE. The difference in active layer thickness tolerance between PM7 D1 and PM7 D2 is rationalized by extracting the energetic disorder (σ) for hole transport using temperature dependent space-charge limited current studies. In the end, this study conveys how small changes to polymer structure, such as side chain placement, may have a small effect on thin-film polymer properties and device performance, but significant differences are realized when charges are transported over longer distances (thicker films, >150 nm).

Low cost photovoltaic materials and green solvent processing are important issues for commercial application of organic solar cells (OSCs). Here, we fabricated high-performance OSCs based on the low-cost conjugated polymer PTQ10 as a donor and the small molecule n-type organic semiconductor HO-IDIC-2F as an acceptor, using non-halogen tetrahydrofuran (THF) as the processing solvent. The power conversion efficiency (PCE) of the as-cast OSCs reached 12.20%, which is comparable with the ones processed with chloroform (CF) (12.43%). Thermal stability of the active layer was also studied by thermal treatment at 100 °C for 8 hours. As a result, the active layer morphology remained unchanged and the PCE of the devices still reached 12.13%, indicating a good thermal-stability of the PTQ10:HO-IDIC-2F blend film. As is commonly known, for OSCs fabricated on larger scales, the layer-by-layer (LL) method generally provides more advantages than the traditional D–A blend solution-processing method. Therefore, to test the compatibility of the THF solvent in the LL method, we fabricated blade-coated LL devices with THF as a single type of solvent for both the donor and acceptor, and the PCE could reach up to 11.85%. The surprisingly high performance of the blade-coated OSC based on the green solvent indicates that PTQ10 is a promising donor to be processed in green solvent for LL technology in the future.