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The increasing energy demands of the global community can be met with solar energy. Solution-processed organic solar cells have seen great progress in power conversion efficiencies (PCEs). Semitransparent organic solar cells (ST-OSCs) have made enormous progress in recent years and have been considered one of the most promising solar cell technologies for applications in building-integrated windows, agricultural greenhouses, and wearable energy resources. Therefore, through the synergistic efforts of transparent electrodes, engineering in near-infrared photoabsorbent materials, and device engineering, high-performance ST-OSCs have developed, and PCE and average visible transmittance reach over 10% and 40%, respectively. In this review, we present the recent progress in photoabsorbent material engineering and strategies for enhancing the performance of ST-OSCs to help researchers gain a better understanding of structure–property–performance relationships. To conclude, new design concepts in material engineering and outlook are proposed to facilitate the further development of high-performance ST-OSCs. [ABSTRACT FROM AUTHOR]

Organic solar cells have obtained a prodigious amount of attention in photovoltaic research due to their unique features of light weight, low cost, eco-friendliness, and semitransparency. A rising trend in this field is the development of all-small-molecules organic solar cells (ASM-OSCs) due to their merits of excellent batch-to-batch reproducibility, well-defined structures, and simple purification. Among the numerous organic photovoltaic (OPV) materials, benzodithiophene (BDT)-based small molecules have come to the fore in achieving outstanding power conversion efficiency (PCE) and breaking the 17% efficiency barrier in single-junction OPV devices, indicating the significant potential of this class of materials in commercial photovoltaic applications. This review specially focuses on up-to-date information about improvements in BDT-based ASM-OSCs since 2011 and provides an outlook on the most significant challenges that remain in the field. We believe there will be more exciting BDT-based photovoltaic materials and devices developed in the near future. [ABSTRACT FROM AUTHOR]

Hole transporting materials (HTMs) with high charge carrier mobilities and receptive functionalities have gained significant attention recently due to their direct effect on boosting the efficiency and lifetime of perovskite solar cells (PVSCs). Herein, two new simple small molecular diketopyrrolopyrrole-based HTMs with different central π-bridges (thieno[3,2-b]thiophene (DPP-TT), and dithieno[3,2-b : 2′,3′-d] thiophene (DPP-DTT)) were synthesized via a facile molecular engineering approach. Both small molecules exhibited strong absorption between 500 and 750 nm and an optical bandgap of ∼1.48 and 1.52 eV; however, their crystalline natures were significantly different, resulting in marked differences in their coating ability and PVSC performances. Thus, optimized DPP-TT-based PVSC devices with a lithium (bis(trifluoromethanesulfonyl)imide) dopant demonstrated a maximum PCE of 15.57% with superior energy level matching and an optimal trade-off between aggregation and processability, resulting in effective perovskite layer passivation via high surface coverage and suppression of charge recombination. In comparison, DPP-DTT had a slightly lower PCE of 14.49%, attributed to its poor film quality caused by its high aggregation tendency. Additionally, these HTMs delivered superior stability owing to superior hydrophobic characteristics. These findings provide valuable insight into the design of new HTMs with varying central π-bridge, which is a simple and effective approach. [ABSTRACT FROM AUTHOR]

The effect of the cross‐coupling catalyst tetrakis(triphenylphosphine)palladium(0) (Pd(PPh3)4) on the performance of a model organic bulk‐heterojunction solar cell composed of a blend of poly([2,6′‐4,8‐di(5‐ethylhexylthienyl)benzo[1,2‐b;3,3‐b]dithiophene]{3‐fluoro‐2[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl}) (PTB7‐Th) donor and 3,9‐bis(2‐methylene‐((3‐(1,1‐dicyanomethylene)‐6,7‐difluoro)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene (IOTIC‐4F) non‐fullerene acceptor is investigated. The effect of intentional addition of different amounts of Pd(PPh3)4 on morphology, free charge carrier generation, non‐geminate bulk trap‐ and surface trap‐assisted recombination as well as bimolecular recombination and charge extraction is quantified. This work shows that free charge carrier generation is affected significantly, while the impact of Pd(PPh3)4 on non‐geminate recombination processes is limited because the catalyst does not facilitate efficient trap‐assisted recombination. The studied system shows substantial robustness towards the addition of Pd(PPh3)4 in small amounts. [ABSTRACT FROM AUTHOR]

The relationship of the temperature–light intensity dependence of open‐circuit voltage Voc in nonfullerene‐based organic solar cells with their material characteristics and multimechanism recombination parameters is described. The systematic variation of the effective bandgap Eg,eff and the electrode layers allows the observation of different relative contributions of bimolecular, bulk, and surface trap‐assisted recombination mechanisms. The complementary advantages of the analytical model and the established voltage‐impedance spectroscopy technique provide a useful tool to quantify multimechanism recombination parameters, effective density of states Nc, and energetic disorder σ in organic solar cells under operating conditions. The validity of the proposed model to understand the temperature and light intensity dependent of Voc is shown by applying it to four different donor:nonfullerene acceptor blend systems with conventional or inverted device architectures. [ABSTRACT FROM AUTHOR]

The short‐circuit current (Jsc) of organic solar cells is defined by the interplay of exciton photogeneration in the active layer, geminate and non‐geminate recombination losses and free charge carrier extraction. The method proposed in this work allows the quantification of geminate recombination and the determination of the mobility‐lifetime product (µτ) as a single integrated parameter for charge transport and non‐geminate recombination. Furthermore, the extraction efficiency is quantified based on the obtained µτ product. Only readily available experimental methods (current‐voltage characteristics, external quantum efficiency measurements) are employed, which are coupled with an optical transfer matrix method simulation. The required optical properties of common organic photovoltaic (OPV) materials are provided in this work. The new approach is applied to three OPV systems in inverted or conventional device structures, and the results are juxtaposed against the µτ values obtained by an independent method based on the voltage–capacitance spectroscopy technique. Furthermore, it is demonstrated that the new method can accurately predict the optimal active layer thickness. [ABSTRACT FROM AUTHOR]

Even though significant breakthroughs with over 18% power conversion efficiencies (PCEs) in polymer:non‐fullerene acceptor (NFA) bulk heterojunction organic solar cells (OSCs) have been achieved, not many studies have focused on acquiring a comprehensive understanding of the underlying mechanisms governing these systems. This is because it can be challenging to delineate device photophysics in polymer:NFA blends comprehensively, and even more complicated to trace the origins of the differences in device photophysics to the subtle differences in energetics and morphology. Here, a systematic study of a series of polymer:NFA blends is conducted to unify and correlate the cumulative effects of i) voltage losses, ii) charge generation efficiencies, iii) non‐geminate recombination and extraction dynamics, and iv) nuanced morphological differences with device performances. Most importantly, a deconvolution of the major loss processes in polymer:NFA blends and their connections to the complex BHJ morphology and energetics are established. An extension to advanced morphological techniques, such as solid‐state NMR (for atomic level insights on the local ordering and donor:acceptor ππ interactions) and resonant soft X‐ray scattering (for donor and acceptor interfacial area and domain spacings), provide detailed insights on how efficient charge generation, transport, and extraction processes can outweigh increased voltage losses to yield high PCEs. [ABSTRACT FROM AUTHOR]

Three symmetrically difluorinated organic semiconductors (namely D5T2F‐P, D5T2F‐S, and D5T2F‐T) containing rhodanine‐flanked pentathiophene structures are synthesized and used as donors in all‐small‐molecule organic solar cells (ASM‐OSCs) prepared with the small‐molecule acceptor 2,2′‐((2Z,2′Z)‐((4,4,9,9‐tetrahexyl‐4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene‐2,7‐diyl)bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile (IDIC‐4F). The different substitutional positions of fluorine atoms (–F) in the conjugated backbone of the donor molecule lead to various material and photovoltaic properties being exhibited. Among the three isomers, the centrally fluorinated D5T2F‐P exhibits a redshifted absorption spectrum, downshifted highest occupied molecular orbital (HOMO) energy level, and improved miscibility with IDIC‐4F in the blend films, all of which result in superior device performance. The power conversion efficiency (PCE) of the ASM‐OSCs based on D5T2F‐P:IDIC‐4F reaches an impressive value of 9.36% with an open‐circuit voltage (VOC) value of 0.86 V and a short‐circuit current density (JSC) value of 16.94 mA cm−2, whereas those of D5T2F‐S (6.11%) and D5T2F‐T (5.42%) are much lower. In comparison, an ASM‐OSC based on the nonfluorinated analogue DRCN5T fabricated under the same conditions exhibits poorer performance (8.03% with IDIC‐4F), revealing 16% enhancement in the PCE achieved through backbone fluorination. The PCE of 9.36% may be one of the highest efficiencies of oligothiophene‐based ASM‐OSCs reported in the literature to date. [ABSTRACT FROM AUTHOR]

Abstract: A series of narrow bandgap electron acceptors is designed and synthesized for efficient near‐infrared (NIR) organic solar cells. Extending π‐conjugation of donor frameworks leads to an intense intramolecular charge transfer, resulting in broad absorption profiles with band edge reaching 950 nm. When blended with an electron donor polymer PTB7‐Th, IOTIC‐2F exhibits efficient charge transfer even with a small energetic offset, so as to achieve a large photogenerated current over 22 mA cm−2 with small energy losses (≈0.49 eV) in solar cell devices. With an intense NIR absorbance, PTB7‐Th:IOTIC‐2F‐based cells achieve a power conversion efficiency of 12.1% with good visible transparency (52% transmittance from 370 to 740 nm). Analysis of film morphology reveals that processing with solvent additives enhances crystalline features of acceptor components, while keeping an appropriate level of donor:acceptor intermixing in the binary blends. The incorporation of the third component, ITIC‐2F, into the PTB7‐Th:IOTIC‐2F blends increases the device efficiency up to 12.9%. The improvement is assigned to the cascaded energy‐level structure and desirable nanoscale phase separation of the ternary blends, which is beneficial to the photocurrent generation. This work provides an efficient molecular design strategy to optimize nonfullerene acceptor properties for efficient NIR organic photovoltaics. [ABSTRACT FROM AUTHOR]

Abstract: Two narrow bandgap non‐fullerene acceptors (NBG‐NFAs), namely, COTIC‐4F and SiOTIC‐4F, are designed and synthesized for the fabrication of efficient near‐infrared organic solar cells (OSCs). The chemical structures of the NBG‐NFAs contain a D′‐D‐D′ electron‐rich internal core based on a cyclopentadithiophene (or dithienosilole) (D) and alkoxythienyl (D′) core, end‐capped with the highly electron‐deficient unit 2‐(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene)malononitrile (A), ultimately providing a A‐D′‐D‐D′‐A molecular configuration that enhances the intramolecular charge transfer characteristics of the excited states. One can thereby reduce the optical bandgap (Egopt) to as low as ≈1.10 eV, one of the smallest values for NFAs reported to date. In bulk‐heterojunction (BHJ) OSCs, NBG‐NFA blends with the polymer donor PTB7‐Th yield power conversion efficiencies (PCE) of up to 9.0%, which is particularly high when compared against a range of NBG BHJ blends. Most significantly, it is found that, despite the small energy loss (Egopt − eVOC) of 0.52 eV, the PTB7‐Th/NBG‐NFA bulk heterojunction blends can yield short‐circuit current densities of up to 22.8 mA cm−2, suggesting that the design and application of NBG‐NFA materials have substantial potential to further improve the PCE of OSCs. [ABSTRACT FROM AUTHOR]

In this study, a comprehensive analytical model to quantify the total nongeminate recombination losses, originating from bimolecular as well as bulk and surface trap‐assisted recombination mechanisms in nonfullerene‐based bulk heterojunction organic solar cells is developed. This proposed model is successfully employed to obtain the different contributions to the recombination current of the investigated solar cells under different illumination intensities. Additionally, the model quantitatively describes the experimentally measured open‐circuit voltage versus light intensity dependence. Most importantly, it is possible to calculate the experimental results with the same fitting parameter values from the presented model. The validity of this model is also proven by a combination of other independent, steady‐state, and transient experimental techniques. This new powerful analytical tool will enable researchers in the photovoltaic community to take into account the synergetic contribution from all relevant types of nongeminate recombination losses in different optoelectronic systems and target their analysis of recombination dynamics at any operating voltage. [ABSTRACT FROM AUTHOR]

In article number 1500802, Kilwon Cho and co‐workers report charge‐carrier‐selective extraction through ferroelectric‐semiconductor hybrid interlayers in organic solar cells. The electrically polarized ferroelectric domains provide directional charge carrier extraction even with non‐Ohmic cathodes, thereby significantly reducing non‐geminate charge carrier recombination within the organic solar cells. [ABSTRACT FROM AUTHOR]

Solution-processed organic solar cells (OSCs) have great promise for next-generation solar energy conversion technologies. Innovative acceptors are constantly being designed to improve device efficiency. In this work, we designed and synthesized a series of A–π–D–π–A type non-fullerene acceptor (NFA) molecules, named IB-TOT, IB-TOM, IB-IOO, and IB-IOM for their applications in OSCs. All molecules showed high thermal stability, broad photoabsorption, and relatively lower highest occupied molecular orbital (HOMO) energy levels from −5.48 eV to −5.58 eV. The optimized OSCs based on these NFAs and PTB7-Th donor deliver power conversion efficiencies (PCEs) of 8.19%, 5.50%, 2.42%, and 3.10% for IB-TOT, IB-TOM, IB-IOO, and IB-IOM molecules, respectively. The higher PCE of IB-TOT-based OSCs is attributed to their excellent miscibility and superior interpenetrating network morphology compared to the other three compounds. These results demonstrate that using the 3-ethylrhodanine acceptor unit to construct the NFA molecule is a successful approach for outstanding achievement in OSCs. • Four IDT-based NFA molecules were designed and synthesized. • The impact of various end-groups on device performance was fully discussed. • An empirical relationship between the end groups was established. • The best-performing OSCs achieved a maximum PCE of 8.19%. • The work promotes future OSC performance enhancement. [ABSTRACT FROM AUTHOR]

• Poly(styrene- co -acrylic acid) nanoparticles are synthesized via emulsion polymerization. • Poly(styrene- co -acrylic acid) nanoparticle films are applied as antireflection layers. • The antireflective coatings increase the light absorption efficiency of the solar cells. • Specifically, the efficiency of the solar cell is improved due to increased photocurrent generation. A simple method is described herein for the preparation of highly transparent antireflection (AR) coatings based on polymeric nanoparticles (NPs) for efficient organic solar cells. The NPs based on poly(styrene- co -acrylic acid) (PS- co -PAA) are synthesized via a straightforward emulsion polymerization process, and air void-containing AR films are deposited onto the glass sides of organic solar cells via spin-casting of the NP solution. Various NP sizes ranging from 42 to 86 nm are used to provide a variety of pore fractions and refractive indices. The AR film with an average particle size of 86 nm is shown to increase the normal-incident 595-nm light transmittance from 92.0 to 98.9%. The AR coatings on solar cells are beneficial for the light absorption of the photoactive layers, thus resulting in enhanced short-circuit current densities of up to ∼26.8 mA cm-2. The power conversion efficiency of the device with the optimum AR coating is increased to 12.8% compared to that of non-AR device (12.0%). This work represents a simple strategy for developing high-performance solar cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • We report a cyano-containing conjugated polymer, PBDT2CNBT, which functionalizes perovskite crystalline domains for defect passivation and charge carrier extraction. • The cyano groups can effectively passivate such defects by achieving strong interactions between the conjugated polymer and perovskite components. • PBDT2CNBT polymer infiltrates the grain boundaries of the perovskite crystals, making the intrinsically detrimental grain boundary beneficial for defect-free properties and enhances charge collection. The grain boundaries in polycrystalline metal-halide perovskite films contain numerous defects, which contribute to performance loss and degradation in perovskite solar cells. In this study, we report a cyano-containing conjugated polymer, composed of benzodithiophene and bicyanobenzothiadiazole (PBDT2CNBT), that functionalizes perovskite crystalline domains for defect passivation and charge carrier extraction. We demonstrate that cyano groups can effectively passivate these defects through strong interactions between the conjugated polymer and perovskite components. The PBDT2CNBT polymer not only modifies the perovskite film surface but also infiltrates the grain boundaries during perovskite crystallization. Notably, these conjugated polymers create favorable energy band bending at the boundary interface between the perovskite and conjugated polymer, enhancing charge separation and collection through grain boundaries by forming a cascade energy level structure. Consequently, we show that PBDT2CNBT transforms the intrinsically detrimental grain boundary into a beneficial feature for defect-free properties and improved charge collection. These advantages directly contribute to achieving high power conversion efficiencies of up to 22.9% and enhanced light, humidity, and thermal stability in perovskite solar cells. This study offers a novel strategy for developing multifunctional conjugated polymers for next-generation perovskite optoelectronics. [ABSTRACT FROM AUTHOR]

• Polymer donors are suitable for semi-transparent organic solar cells. • PL1 and PL2 can selectively absorb the light in NIR region. • The difference of steric structure of PL1 and PL2 affects device parameters. • PL2-based semi-transparent device presents 40.4% of AVT and 4.00% of LUE. Semi-transparent organic solar cells (ST-OSCs) have attracted significant attention for various applications such as building-integrated photovoltaics and smart window technologies. Although various low-band gap non-fullerene acceptors have been developed, near-infrared (NIR) absorbing polymeric donors have been rarely reported for highly efficient ST-OSCs. In this study, we synthesize cyclopentadithiophene (CPDT) core-based NIR-absorbing polymer donors, PL1 and PL2. These polymer donors show strong NIR absorption capabilities with high transmittance in visible wavelength region and deep-lying HOMO levels for cascade energy level alignment with low-bandgap non-fullerene acceptors. The opaque device with PL2 and PCBM exhibits higher power conversion efficiency of 11.62% than that of the device with PL1 (PCE: 7.54%) due to lower charge-carrier recombination loss and balanced charge-carrier mobilities. Most significantly, incorporation of PL2 into ST-OSCs results in a PCE of 9.91 %, average visible transmittance of 40.4 % and light utilization efficiency (LUE) of 4.00 %. This work achieves the one of the highest LUE in ST-OSCs based on new NIR-absorbing polymer donors. [ABSTRACT FROM AUTHOR]