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Following the 2nd release of the "Emerging PV reports," the best achievements in the performance of emerging photovoltaic devices in diverse emerging photovoltaic research subjects are summarized, as reported in peer‐reviewed articles in academic journals since August 2021. Updated graphs, tables, and analyses are provided with several performance parameters, e.g., power conversion efficiency, open‐circuit voltage, short‐circuit current density, fill factor, light utilization efficiency, and stability test energy yield. These parameters are presented as a function of the photovoltaic bandgap energy and the average visible transmittance for each technology and application, and are put into perspective using, e.g., the detailed balance efficiency limit. The 3rd installment of the "Emerging PV reports" extends the scope toward triple junction solar cells. [ABSTRACT FROM AUTHOR]

Following the 1st release of the "Emerging photovoltaic (PV) reports", the best achievements in the performance of emerging photovoltaic devices in diverse emerging photovoltaic research subjects are summarized, as reported in peer‐reviewed articles in academic journals since August 2020. Updated graphs, tables, and analyses are provided with several performance parameters, e.g., power conversion efficiency, open‐circuit voltage, short‐circuit current density, fill factor, light utilization efficiency, and stability test energy yield. These parameters are presented as a function of the photovoltaic bandgap energy and the average visible transmittance for each technology and application and are put into perspective using, e.g., the detailed balance efficiency limit. The 2nd instalment of the "Emerging PV reports" extends the scope toward tandem solar cells and presents the current state‐of‐the‐art in tandem solar cell performance for various material combinations. [ABSTRACT FROM AUTHOR]

Emerging photovoltaics (PVs) focus on a variety of applications complementing large scale electricity generation. Organic, dye‐sensitized, and some perovskite solar cells are considered in building integration, greenhouses, wearable, and indoor applications, thereby motivating research on flexible, transparent, semitransparent, and multi‐junction PVs. Nevertheless, it can be very time consuming to find or develop an up‐to‐date overview of the state‐of‐the‐art performance for these systems and applications. Two important resources for recording research cells efficiencies are the National Renewable Energy Laboratory chart and the efficiency tables compiled biannually by Martin Green and colleagues. Both publications provide an effective coverage over the established technologies, bridging research and industry. An alternative approach is proposed here summarizing the best reports in the diverse research subjects for emerging PVs. Best performance parameters are provided as a function of the photovoltaic bandgap energy for each technology and application, and are put into perspective using, e.g., the Shockley–Queisser limit. In all cases, the reported data correspond to published and/or properly described certified results, with enough details provided for prospective data reproduction. Additionally, the stability test energy yield is included as an analysis parameter among state‐of‐the‐art emerging PVs. [ABSTRACT FROM AUTHOR]

The tandem concept involves stacking two or more cells with complementary absorption spectra in series or parallel connection, harvesting photons at the highest possible potential. It is strongly suggested that the roll-to-roll production of organic solar cells will employ the tandem concept to enhance the power conversion efficiency (PCE). However, due to the undeveloped deposition techniques, the challenges in ink formulation as well as the lack of commercially available high performance active materials, roll-to-roll fabrication of highly efficient organic tandem solar cells currently presents a major challenge. The reported high PCE values from lab-scale spin-coated devices are, of course, representative, but not helpful for commercialization. Here, organic tandem solar cells with exceptionally high fill factors and PCE values of 7.66% (on glass) and 5.56% (on flexible substrate), which are the highest values for the solution-processed tandem solar cells fabricated by a mass-production compatible coating technique under ambient conditions, are demonstrated. To predict the highest possible performance of tandem solar cells, optical simulation based on experimentally feasible values is performed. A maximum PCE of 21% is theoretically achievable for an organic tandem solar cell based on the optimized bandgaps and achieved fill factors. [ABSTRACT FROM AUTHOR]

Photovoltaic tandem technology has the potential to boost the power conversion efficiency of organic photovoltaic devices. Here, a reliable and efficient fully solution-processed intermediate layer (IML) consisting of ZnO and neutralized poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is demonstrated for series-connected multi-junction organic solar cells (OSCs). Drying at 80 °C in air is sufficient for this solution-processed IML to obtain excellent functionality and reliability, which allow the use of most of high performance donor materials in the tandem structure. An open circuit voltage ( Voc) of 0.56 V is obtained for single-junction OSCs based on a low band-gap polymer, while multi-junction OSCs based on the same absorber material deliver promising fill factor values along with fully additive Voc as the number of junctions increase. Optical and electrical simulations, which are reliable and promising guidelines for the design and investigation of multi-junction OSCs, are discussed. The outcome of optical and electrical simulations is in excellent agreement with the experimental data, indicating the outstanding efficiency and functionality of this solution-processed IML. The demonstration of this efficient, solution-processed IML represents a convenient way for facilitating fabrication of multi-junction OSCs to achieve high power conversion efficiency. [ABSTRACT FROM AUTHOR]

A new donor-acceptor copolymer consisting of triazoloquinoxaline and 9,9-dialkylfluorene units on the main chain has been synthesized, characterized and evaluated as donor material in bulk heterojunction solar cells using PC61BM as an acceptor. The resulting polymer PTQF showed good thermal stability and solubility in common organic solvents. Cyclic Voltammetry measurements showed that the PTQF has HOMO-LUMO energy levels of −5.13 and −3.62 eV, respectively. DFT calculations revealed that the HOMO is delocalized all over the thiophene and fluorene units and the LUMO is localized mainly on the triazole and pyrazine units. PTQF absorbs broadly in the visible region and exhibits a bandgap of 1.4 eV. Photovoltaic devices exhibited 1.7% efficiency for 1:2 PTQF:PC61BM blend ratio using Ca/Ag electrodes. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 [ABSTRACT FROM AUTHOR]

Two‐photon Polymerization (2PP) process for high‐resolution 3D printing presents an opportunity to design micro‐scale structures with a high surface‐to‐volume ratio for highly responsive devices. However, these acrylate or thiol‐based resins are electrically insulating and non‐functional in nature, therefore limiting their widespread application in biosensing and biotechnology. Here, a novel conductive polymeric composite resin to print conductive 3D micro‐structures via the 2PP technique is developed and its application in sensing are demonstrated. The composite consists of acrylate‐based 2PP resin and Poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS), a conductive and biocompatible organic semiconductor The PEDOT:PSS incorporation in resin through Raman and X‐ray photoelectron spectroscopy (XPS) is studied. An electrical conductivity of 3.5 × 102 S cm−1 in a 20 µm long and 10 µm high 3D printed micro‐structure which is suitable for electronic applications is achieved. An ultra‐fast micro‐3D printed humidity sensor with a response and recovery time of 0.15 and 0.3 s respectively is demonstrated. The printed sensors show high sensitivity in humidity levels of 0–80%RH. As a proof of concept, the real‐time respiration of a human body is recorded, implying a potential application in health monitoring systems. [ABSTRACT FROM AUTHOR]

Recent advances in light‐responsive materials enabled the development of devices that can wirelessly activate tissue with light. Here it is shown that solution‐processed organic heterojunctions can stimulate the activity of primary neurons at low intensities of light via photochemical reactions. The p‐type semiconducting polymer PDCBT and the n‐type semiconducting small molecule ITIC (a non‐fullerene acceptor) are coated on glass supports, forming a p–n junction with high photosensitivity. Patch clamp measurements show that low‐intensity white light is converted into a cue that triggers action potentials in primary cortical neurons. The study shows that neat organic semiconducting p–n bilayers can exchange photogenerated charges with oxygen and other chemical compounds in cell culture conditions. Through several controlled experimental conditions, photo‐capacitive, photo‐thermal, and direct hydrogen peroxide effects on neural function are excluded, with photochemical delivery being the possible mechanism. The profound advantages of low‐intensity photo‐chemical intervention with neuron electrophysiology pave the way for developing wireless light‐based therapy based on emerging organic semiconductors. [ABSTRACT FROM AUTHOR]

Solution‐processable halide perovskites have emerged as strong contenders for next‐generation solar cells owing to their favorable optoelectronic properties. To maintain the efficiency momentum of perovskite solar cells (PSCs), development of advanced processing techniques, particularly for the perovskite layer, is imperative. There is a close correlation between the quality of the perovskite layer and its photophysical properties: Highly crystalline large grains with uniform morphology of the perovskite layer and their interface with charge transporters are crucial for achieving high performance. Significant efforts have been dedicated to achieve perovskite films with large grains reaching the millimeter‐scale for high‐efficiency PSCs. Recent work showcases a transition from large grain polycrystalline to single‐crystalline (SC) PSCs made possible by the facile growth of perovskite single crystals. In this review, the recent progress of the large grain polycrystalline PSCs and grain boundary‐free SC‐PSCs is reported, particularly focusing on the recent approach of depositing large‐grained perovskite layers and single crystal growth technique, that have been adopted for fabrication of efficient PSCs. In addition, prospects of SC‐PSCs and their further development in terms of efficiency, device design, scalability, and stability are discussed. [ABSTRACT FROM AUTHOR]

Non‐fullerene acceptor (NFA)‐based ternary bulk heterojunction solar cells (TSC) are the most efficient organic solar cells (OSCs) today due to their broader absorption and quantum efficiencies (QE) often surpassing those of corresponding binary blends. The impact on QE of the energetics driving charge transfer at the electron donor:electron acceptor (D/A) interfaces is studied in blends of PBDB‐T‐2F donor with several pairs of lower bandgap NFAs. As in binary blends, the ionization energy offset between donor and acceptor (ΔIE) controls the QE and maximizes for ΔIE > 0.5 eV. However, ΔIE is not controlled by the individual NFAs IEs but by their average, weighted for their blending ratio. Using this property, the QE of a PBDB‐T‐2F:IEICO binary blend that has an insufficient ΔIE for charge generation is improved by adding a deep IE third component: IT‐4F. Combining two NFAs enables to optimize the D/A energy alignment and cells' QE without molecular engineering. [ABSTRACT FROM AUTHOR]

The organic photodiode (OPD) is a promising building block for solution‐processable, flexible, lightweight, and miniaturized photodetectors, ideal for wearable applications. Despite the advances in materials used in OPDs, their photocurrent and light responsivity are limited, and alternative methods are required to boost the signal response. Herein, a miniaturized organic electrochemical transistor (OECT) is integrated with an OPD module to unlock the potential of OPDs to acquire physiological signals. In this integrated photodetector (IPD) system, the light intensity regulates the OPD voltage output that modulates the OECT channel current. The high transconductance of the OECT provides efficient voltage‐to‐current conversion, enhancing the signal‐to‐noise ratio on the sensing site. A microscale, p‐type enhancement‐mode OECT with high gm and fast switching speed performs better in this application than depletion‐mode OECT of the same geometry. The IPD achieves a photocurrent and responsivity 318 and 140 times higher than the standalone OPD, respectively. It is shown that with the IPD, the amplitude of the photoplethysmogram signals detected by the OPD is enhanced by a factor of 2.9 × 103, highlighting its potential as a wearable biosensor and to detect weak, often uncaptured, light‐based signals from living systems. [ABSTRACT FROM AUTHOR]

Efficiencies of organic solar cells have practically doubled since the development of non‐fullerene acceptors (NFAs). However, generic chemical design rules for donor‐NFA combinations are still needed. Such rules are proposed by analyzing inhomogeneous electrostatic fields at the donor–acceptor interface. It is shown that an acceptor–donor–acceptor molecular architecture, and molecular alignment parallel to the interface, results in energy level bending that destabilizes the charge transfer state, thus promoting its dissociation into free charges. By analyzing a series of PCE10:NFA solar cells, with NFAs including Y6, IEICO, and ITIC, as well as their halogenated derivatives, it is suggested that the molecular quadrupole moment of ≈75 Debye Å balances the losses in the open circuit voltage and gains in charge generation efficiency. [ABSTRACT FROM AUTHOR]

An equivalent ohmic contact is successfully formed between low‐conductivity poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS) and solution‐processed aluminum‐doped ZnO (AZO). Because of its promising optical and electrical properties, this combination can serve as an efficient interconnection layer as well as an optical spacer in inverted‐structure organic tandem devices. [ABSTRACT FROM AUTHOR]

Tuning the bandgap of electrochromic polymers is one of the important research topics in electrochromism. To understand clearly the effect of donor unit in donor-acceptor-donor-type polymers, 2,3-bis(4- tert-butylphenyl)-5,8-di(thiophen-2-yl)quinoxaline and 2,3-bis(4- tert-butylphenyl)-5-(2,3-dihydrothieno[3,4- b][1,4]dioxin- 5-yl)-8-(thiophen-2-yl)quinoxaline were synthesized and polymerized potentiodynamically. Their electrochemical and spectroelectrochemical studies were performed, and the results were compared with those of poly(2,3-bis(4- tert-butylphenyl)-5,8-bis(2,3-dihydrothieno[3,4- b][1,4]dioxin-5-yl)quinoxaline) (Gunbas et al., Adv Mater 2008, 20, 691-695). A blue shift in the polymer π-π* transitions revealed that the bandgap of such polymers with the same acceptor unit is related to the electron density of donor units. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 [ABSTRACT FROM AUTHOR]

Sputtered nickel oxide (NiOx) is an attractive hole‐transport layer for efficient, stable, and large‐area p‐i‐n metal‐halide perovskite solar cells (PSCs). However, surface traps and undesirable chemical reactions at the NiOx/perovskite interface are limiting the performance of NiOx‐based PSCs. To address these issues simultaneously, an efficient NiOx/perovskite interface passivation strategy by using an organometallic dye molecule (N719) is reported. This molecule concurrently passivates NiOx and perovskite surface traps, and facilitates charge transport. Consequently, the power conversion efficiency (PCE) of single‐junction p‐i‐n PSCs increases from 17.3% to 20.4% (the highest reported value for sputtered‐NiOx based PSCs). Notably, the N719 molecule self‐anchors and conformally covers NiOx films deposited on complex surfaces. This enables highly efficient textured monolithic p‐i‐n perovskite/silicon tandem solar cells, reaching PCEs up to 26.2% (23.5% without dye passivation) with a high processing yield. The N719 layer also forms a barrier that prevents undesirable chemical reactions at the NiOx/perovskite interface, significantly improving device stability. These findings provide critical insights for improved passivation of the NiOx/perovskite interface, and the fabrication of highly efficient, robust, and large‐area perovskite‐based optoelectronic devices. [ABSTRACT FROM AUTHOR]

Monolithically stacked tandem solar cells present opportunities to absorb more of the sun's radiation while reducing the degree of energetic loss through thermalization. In these applications, the bandgap of the tandem's constituent subcells must be carefully adjusted so as to avoid competition for photons. Organic photovoltaics based on nonfullerene acceptors (NFAs) have recently exploded in popularity owing to the ease with which their electrical and optical properties can be tuned through chemistry. Here, highly complementary and efficient 2‐terminal tandem solar cells are reported based on a wide bandgap amorphous silicon absorber, and a narrow bandgap NFA bulk‐heterojunction with power conversion efficiencies (PCEs) exceeding 15%. Interface engineering of this tandem device allows for high PCEs across a wide range of light intensities both above and below "1 sun." Furthermore, the addition of an inorganic silicon subcell enhances the operational stability of the tandem by reducing the light‐stress experienced by the bulk heterojunction, resolving a long‐standing stumbling block in organic photovoltaic research. [ABSTRACT FROM AUTHOR]

Slot‐die (SD) coating is used to fabricate fully solution processed organic solar cells (OSCs) based on a blend of high performance donor polymer (PTB7‐Th) and a non‐fullerene acceptor (IEICO‐4F) for stable devices over extended periods of operation. The optimization of a sequential deposition process of transport and active layers, under ambient conditions, enable high efficiency slot‐die coated solar cells with remarkable power conversion efficiencies (PCE) > 11.0% to bridge the gap between lab‐to‐fab. Fully slot‐die coated inverted OSCs are demonstrated with efficiencies reaching 11% along with 1 cm2 devices, proving the scalability and reproducibility of the proposed technique. Further, replacing the evaporated Ag electrode with solution processed Ag nanowire (AgNW) electrodes shows the highest light utilization efficiency of 5.26% for semi‐transparent OSC with a PCE of 9.07% and average visible transmission of 58%. [ABSTRACT FROM AUTHOR]

New polymer donors and nonfullerene acceptors have elevated the performance and stability of solar cells to higher grounds. To achieve their full potential, they require their adaptation to scalable and cost‐effective solution manufacturing techniques for large area deposition. Likewise, formulating scalable solution‐based transport layer inks that are compatible with the photoactive layer is imperative. This manuscript reports the full integration of solution‐based transport layers and electrode alongside a PTB7‐Th:IEICO‐4F bulk heterojunction in inverted architecture through inkjet‐printing, resulting in power conversion efficiencies up to 12.4% opaque devices and 9.5% semitransparent devices with average visible transmittance values of 50.1%, including hole transport layer. The wetting envelope of the highly‐hydrophobic photoactive layer alongside the surface energy of candidate solutions and solvents allows the formulation of thick transport layer inks that are compatible with the drop‐on‐demand inkjet‐printing process and yield uniform and homogenous films. Moreover, the surface energy components of the donor and acceptor serves as a fingerprint to assess the vertical stratification of the photoactive layer with the inclusion of different solvents. This methodology addresses a scale‐up bottleneck of solution‐based transport layers for high‐efficiency organic cells, enabling its adaptation to high‐throughput techniques including slot‐die and roll‐to‐roll coating. [ABSTRACT FROM AUTHOR]

B Organic Bioelectronic b Highly photosensitive, organic p-n junctions stimulate primary neurons when illuminated with low-intensity light I via i photochemical reactions. The profound advantages of low-intensity, photo-chemical intervention with neuron electrophysiology, pave the way for developing wireless, light therapy, based on emerging organic semiconductors. The electrophysiology of primary neurons can be influenced by photochemical reactions, even when these neurons are situated away from the surface of polymers. [Extracted from the article]

While photovoltaic blends based on non‐fullerene acceptors are touted for their thermal stability, this type of acceptor tends to crystallize, which can result in a gradual decrease in photovoltaic performance and affects the reproducibility of the devices. Two halogenated indacenodithienothiophene‐based acceptors that readily co‐crystallize upon mixing are studied, which indicates that the use of an acceptor mixture alone does not guarantee the formation of a disordered mixture. The addition of the donor polymer to the acceptor mixture readily suppresses the crystallization, which results in a fine‐grained ternary blend with nanometer‐sized domains that do not coarsen due to a high Tg ≈ 200 °C. As a result, annealing at temperatures of up to 170 °C does not markedly affect the photovoltaic performance of ternary devices, in contrast to binary devices that suffer from acceptor crystallization in the active layer. The results indicate that the ternary approach enables the use of high‐temperature processing protocols, which are needed for upscaling and high‐throughput fabrication of organic solar cells. Further, ternary devices display a stable photovoltaic performance at 130 °C for at least 205 h, which indicates that the use of acceptor mixtures allows to fabricate devices with excellent thermal stability. [ABSTRACT FROM AUTHOR]

Power conversion efficiencies of perovskite solar cells (PSCs) have rapidly increased from 3.8% to a certified 25.2% within only a decade. Eliminating possible recombination losses at the interfaces is essential to further improve both efficiency and stability of this class of emerging photovoltaic technology. Herein, a simple approach for improving the electron extraction of the PC60BM electron transport layer (ETL) is presented by sequentially depositing Al:ZnO (AZO) and triphenyl‐phosphine oxide (TPPO) on top of it, in a p–i–n device configuration. The efficiency of the resulting CH3NH3PbI3‐based solar cell is shown to improve from 14.6%, measured for the control PC60BM‐only cell, to 17.9% for double‐ETL (PC60BM/AZO) and 19.2% for triple‐ETL (PC60BM/AZO/TPPO)‐based devices, respectively. Optimized triple‐ETL‐based cells exhibit high fill factor of 82%. The combination of electrical and quantum mechanical calculations shows that efficiency improvement is attributed to reduced trap‐assisted recombination at the interface and better energy level alignment due to chemical interactions between PC60BM, AZO, and TPPO. Moreover, it is shown that the use of multilayer ETL results in better device stability (T80 ≈ 800 h) under constant illumination. This work opens new possibilities for inexpensive highly efficient and stable multilayered contacts for PSCs by combining organic small molecules and metal oxides. [ABSTRACT FROM AUTHOR]

Ultra‐lightweight solar cells have attracted enormous attention due to their ultra‐conformability, flexibility, and compatibility with applications including electronic skin or miniaturized electronics for biological applications. With the latest advancements in printing technologies, printing ultrathin electronics is becoming now a reality. This work offers an easy path to fabricate indium tin oxide (ITO)‐free ultra‐lightweight organic solar cells through inkjet‐printing while preserving high efficiencies. A method consisting of the modification of a poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) ink with a methoxysilane‐based cross‐linker (3‐glycidyloxypropyl)trimethoxysilane (GOPS)) is presented to chemically modify the structure of the electrode layer. Combined with plasma and solvent post‐treatments, this approach prevents shunts and ensures precise patterning of solar cells. By using poly(3‐hexylthiophene) along rhodanine‐benzothiadiazole‐coupled indacenodithiophene (P3HT:O‐IDTBR), the power conversion efficiency (PCE) of the fully printed solar cells is boosted up to 4.73% and fill factors approaching 65%. All inkjet‐printed ultrathin solar cells on a 1.7 µm thick biocompatible parylene substrate are fabricated with PCE reaching up to 3.6% and high power‐per‐weight values of 6.3 W g−1. After encapsulation, the cells retain their performance after being exposed for 6 h to aqueous environments such as water, seawater, or phosphate buffered saline, paving the way for their integration in more complex circuits for biological systems. [ABSTRACT FROM AUTHOR]

The recent re‐emergence of halide perovskites has received escalating interest for optoelectronic applications. In addition to photovoltaics, the multifunctional nature of halide perovskites has led to diverse applications. The ultralow thermal conductivity coupled with decent mobility and charge carrier tunability led to the prediction of halide perovskites as a possible contender for future thermoelectrics. Herein, recent advances in thermal transport of halide perovskites and their potentials and challenges for thermoelectrics are reviewed. An overview of the phonon behavior in halide perovskites, as well as the compositional dependency is analyzed. Understanding thermal transport and knowing the thermal conductivity value is crucial for creating effective heat dissipation schemes and determining other thermal‐related properties like thermo‐optic coefficients, hot‐carrier cooling, and thermoelectric efficiency. Recent works on halide perovskite‐based thermoelectrics together with theoretical predictions for their future viability are highlighted. Also, progress on modulating halide perovskite‐based thermoelectric properties using light and chemical doping is discussed. Finally, strategies to overcome the limiting factors in halide perovskite thermoelectrics and their prospects are emphasized. [ABSTRACT FROM AUTHOR]

Abstract: Poly (3‐hexylthiophene) (P3HT) was an early frontrunner in the development of donor polymers to be used in organic photovoltaics. A relatively straightforward and inexpensive synthesis suggests that it may be the most viable donor polymer to use in large‐scale commercial organic solar cells. Replacing fullerenes with new electron acceptors has led to significant improvements in device performance and stability, with devices now able to exceed an efficiency of 7%. Past studies have reported a dependence of device performance on the molecular weight of the polymer in fullerene‐containing blends, however, with nonfullerene acceptors now showing promise a similar study was needed. P3HT blends, with two nonfullerene acceptors (O‐IDTBR and EH‐IDTBR), were probed using a number of polymer batches with varying molecular weights. O‐IDTBR was shown to exhibit a dependence on the polymer molecular weight, with optimal performance achieved with a 34 kDa polymer, while EH‐IDTBR displayed an independence in performance with varying polymer molecular weight. Probing the thermal and morphological behavior of the P3HT:O‐IDTBR blends suggests that an optimal morphology with pronounced donor and acceptor domains was only achieved with the 34 kDa polymer, and a greater degree of mixing was exhibited in the other blends, likely leading to poorer device performance. [ABSTRACT FROM AUTHOR]

Abstract: N‐type organic small molecules (SMs) are attracting attention in the organic electronics field, due to their easy purification procedures with high yield. However, only a few reports show SMs that perform well in both organic field‐effect transistors (OFETs) and organic solar cells (OSCs). Here, the synthesis and characterization of an n‐type small molecule with an indacenodithieno[3,2‐b]thiophene (IDTT) core unit and linear alkylated side chain (C16) (IDTTIC) are reported. Compared to the state‐of‐the‐art n‐type molecule IDTIC, IDTTIC exhibits smaller optical bandgap and higher absorption coefficient, which is due to the enhanced intramolecular effect. After mixing with the polymer donor PBDB‐T, IDTIC‐based solar cells deliver a power conversion efficiency of only 5.67%. In stark contrast, the OSC performance of IDTTIC improves significantly to 11.2%. It is found that the superior photovoltaic properties of PBDB‐T:IDTTIC blends are mainly due to reduced trap‐assisted recombination and enhanced molecular packing coherence length and higher domain purity when compared to IDTIC. Moreover, a significantly higher electron mobility of 0.50 cm2 V−1 s−1 for IDTTIC in OFET devices than for IDTIC (0.15 cm2 V−1 s−1) is obtained. These superior performances in OSCs and OFETs demonstrate that SMs with extended π‐conjugation of the backbone possess a great potential for application in organic electronic devices. [ABSTRACT FROM AUTHOR]

Abstract: The solution‐processed organic photodetectors underpin an emerging technology with inherent implications in the biological sensors and imaging displays. Conventional organic photodiodes, the core element of an organic photodetector, rely mainly on fullerene‐based acceptors, which in combination with high and middle bandgap donors, limit the spectral photosensitivity to the visible range. Even in the case of low bandgap polymers the oscillator strength and thus the extinction coefficient are usually limited in the NIR due to the nature of molecular orbital hybridization. Instead, it is showed that pairing prototypical poly(3‐hexylthiophene) (P3HT) with rhodanine‐benzothiadiazole‐coupled indacenodithiophene (IDTBR), a nonfullerene electron acceptor absorbing beyond 750 nm, as the photoactive material of a simple photodiode results in a highly efficient organic photodetector with a record responsivity of 0.42 A W−1 and external quantum efficiency (EQE) of 69% in the NIR (755 nm). Nonfullerene‐based photodiodes are processed on amorphous silicon active matrix backplanes to realize large area flat panel photodetector imagers able to detect objects under visible and NIR light conditions with an exceptional combination of responsivity, dynamic response and image crosstalk. [ABSTRACT FROM AUTHOR]

Abstract: Organic bulk heterojunction solar cells based on small molecule acceptors have recently seen a rapid rise in the power conversion efficiency with values exceeding 13%. This impressive achievement has been obtained by simultaneous reduction of voltage and charge recombination losses within this class of materials as compared to fullerene‐based solar cells. In this contribution, the authors review the current understanding of the relevant photophysical processes in highly efficient nonfullerene acceptor (NFA) small molecules. Charge generation, recombination, and charge transport is discussed in comparison to fullerene‐based composites. Finally, the authors review the superior light and thermal stability of nonfullerene small molecule acceptor based solar cells, and highlight the importance of NFA‐based composites that enable devices without early performance loss, thus resembling so‐called burn‐in free devices. [ABSTRACT FROM AUTHOR]

Abstract: Nonfullerene acceptors (NFAs) in blends with highly crystalline donor polymers have been shown to yield particularly high device voltage outputs, but typically more modest quantum yields for photocurrent generation as well as often lower fill factors (FF). In this study, we employ transient optical and optoelectronic analysis to elucidate the factors determining device photocurrent and FF in blends of the highly crystalline donor polymer PffBT4T‐2OD with the promising NFA FBR or the more widely studied fullerene acceptor PC71BM. Geminate recombination losses, as measured by ultrafast transient absorption spectroscopy, are observed to be significantly higher for PffBT4T‐2OD:FBR blends. This is assigned to the smaller LUMO‐LUMO offset of the PffBT4T‐2OD:FBR blends relative to PffBT4T‐2OD:PC71BM, resulting in the lower photocurrent generation efficiency obtained with FBR. Employing time delayed charge extraction measurements, these geminate recombination losses are observed to be field dependent, resulting in the lower FF observed with PffBT4T‐2OD:FBR devices. These data therefore provide a detailed understanding of the impact of acceptor design, and particularly acceptor energetics, on organic solar cell performance. Our study concludes with a discussion of the implications of these results for the design of NFAs in organic solar cells. [ABSTRACT FROM AUTHOR]

Organic semiconductors are in general known to have an inherently lower charge carrier mobility compared to their inorganic counterparts. Bimolecular recombination of holes and electrons is an important loss mechanism and can often be described by the Langevin recombination model. Here, the device physics of bulk heterojunction solar cells based on a nonfullerene acceptor (IDTBR) in combination with poly(3-hexylthiophene) (P3HT) are elucidated, showing an unprecedentedly low bimolecular recombination rate. The high fill factor observed (above 65%) is attributed to non-Langevin behavior with a Langevin prefactor (β/βL) of 1.9 × 10−4. The absence of parasitic recombination and high charge carrier lifetimes in P3HT:IDTBR solar cells inform an almost ideal bimolecular recombination behavior. This exceptional recombination behavior is explored to fabricate devices with layer thicknesses up to 450 nm without significant performance losses. The determination of the photoexcited carrier mobility by time-of-flight measurements reveals a long-lived and nonthermalized carrier transport as the origin for the exceptional transport physics. The crystalline microstructure arrangement of both components is suggested to be decisive for this slow recombination dynamics. Further, the thickness-independent power conversion efficiency is of utmost technological relevance for upscaling production and reiterates the importance of understanding material design in the context of low bimolecular recombination. [ABSTRACT FROM AUTHOR]

Recent advances in efficiency of organic photovoltaics are driven by judicious selection of processing conditions that result in a 'desired' morphology. An important theme of morphology research is quantifying the effect of processing conditions on morphology and relating it to device efficiency. State-of-the-art morphology quantification methods provide film-averaged or 2D-projected features that only indirectly correlate with performance, making causal reasoning nontrivial. Accessing the 3D distribution of material, however, provides a means of directly mapping processing to performance. In this paper, two recently developed techniques are integrated-reconstruction of 3D morphology and subsequent conversion into intuitive morphology descriptors -to comprehensively image and quantify morphology. These techniques are applied on films generated by doctor blading and spin coating, additionally investigating the effect of thermal annealing. It is found that morphology of all samples exhibits very high connectivity to electrodes. Not surprisingly, thermal annealing consistently increases the average domain size in the samples, aiding exciton generation. Furthermore, annealing also improves the balance of interfaces, enhancing exciton dissociation. A comparison of morphology descriptors impacting each stage of photophysics (exciton generation, dissociation, and charge transport) reveals that spin-annealed sample exhibits superior morphology-based performance indicators. This suggests substantial room for improvement of blade-based methods (process optimization) for morphology tuning to enhance performance of large area devices. [ABSTRACT FROM AUTHOR]

Organic solar cells that are free of burn-in, the commonly observed rapid performance loss under light, are presented. The solar cells are based on poly(3-hexylthiophene) (P3HT) with varying molecular weights and a nonfullerene acceptor (rhodanine-benzothiadiazole-coupled indacenodithiophene, IDTBR) and are fabricated in air. P3HT:IDTBR solar cells light-soaked over the course of 2000 h lose about 5% of power conversion efficiency (PCE), in stark contrast to [6,6]-Phenyl C61 butyric acid methyl ester (PCBM)-based solar cells whose PCE shows a burn-in that extends over several hundreds of hours and levels off at a loss of ≈34%. Replacing PCBM with IDTBR prevents short-circuit current losses due to fullerene dimerization and inhibits disorder-induced open-circuit voltage losses, indicating a very robust device operation that is insensitive to defect states. Small losses in fill factor over time are proposed to originate from polymer or interface defects. Finally, the combination of enhanced efficiency and stability in P3HT:IDTBR increases the lifetime energy yield by more than a factor of 10 when compared with the same type of devices using a fullerene-based acceptor instead. [ABSTRACT FROM AUTHOR]

The photovoltaic performance and optoelectronic properties of a donor-acceptor copolymer are reported based on indacenodithienothiophene (IDTT) and 2,3-bis(3-(octyloxy)phenyl)quinoxaline moieties (PIDTTQ) as a function of the number-average molecular weight ( Mn). Current-voltage measurements and photoinduced charge carrier extraction by linear increasing voltage (photo-CELIV) reveal improved charge generation and charge transport properties in these high band gap systems with increasing Mn, while polymers with low molecular weight suffer from diminished charge carrier extraction because of low mobility-lifetime ( μτ) product. By combining Fourier-transform photocurrent spectroscopy (FTPS) with electroluminscence spectroscopy, it is demonstrate that increasing Mn reduces the nonradiative recombination losses. Solar cells based on PIDTTQ with Mn = 58 kD feature a power conversion efficiency of 6.0% and a charge carrier mobility of 2.1 × 10−4 cm2 V−1 s−1 when doctor bladed in air, without the need for thermal treatment. This study exhibits the strong correlations between polymer fractionation and its optoelectronics characteristics, which informs the polymer design rules toward highly efficient organic solar cells. [ABSTRACT FROM AUTHOR]

Chemical Design Rules for Non-Fullerene Acceptors in Organic Solar Cells (Adv. Design rules, donor-acceptor interface, non-fullerene acceptors, organic solar cells Keywords: design rules; donor-acceptor interface; non-fullerene acceptors; organic solar cells EN design rules donor-acceptor interface non-fullerene acceptors organic solar cells 1 1 1 11/26/21 20211125 NES 211125 B Non-Fullerene Acceptors b In article number 2102363, Denis Andrienko and co-workers summarize the chemical design rules of non-fullerene acceptor molecules for use in efficient organic solar cells. [Extracted from the article]

Nickel oxide, passivation, perovskites, solar cells, tandems Linked Nickel Oxide/Perovskite Interface Passivation for High-Performance Textured Monolithic Tandem Solar Cells (Adv. Keywords: nickel oxide; passivation; perovskites; solar cells; tandems EN nickel oxide passivation perovskites solar cells tandems 1 1 1 10/29/21 20211027 NES 211027 B Interface Passivation b In article number 2101662, Furkan H. Isikgor, Stefaan De Wolf and co-authors develop a NiO SB I x i sb /perovskite interface passivation strategy using an organometallic dye (N719) molecule. [Extracted from the article]

With the advent of flexible and wearable electronics and sensors, there is an urgent need to develop energy‐harvesting solutions that are compatible with such wearables. However, many of the proposed energy‐harvesting solutions lack the necessary mechanical properties, which make them susceptible to damage by repetitive and continuous mechanical stresses, leading to serious degradation in device performance. Developing new energy materials that possess high deformability and self‐healability is essential to realize self‐powered devices. Herein, a thermoelectric ternary composite is demonstrated that possesses both self‐healing and stretchable properties produced via 3D‐printing method. The ternary composite films provide stable thermoelectric performance during viscoelastic deformation, up to 35% tensile strain. Importantly, after being completely severed by cutting, the composite films autonomously recover their thermoelectric properties with a rapid response time of around one second. Using this self‐healable and solution‐processable composite, 3D‐printed thermoelectric generators are fabricated, which retain above 85% of their initial power output, even after repetitive cutting and self‐healing. This approach represents a significant step in achieving damage‐free and truly wearable 3D‐printed organic thermoelectrics. [ABSTRACT FROM AUTHOR]

High fill factors have only recently become commonplace in nonfullerene‐based organic solar cells, with the balance of charge carrier mobilities often cited as the contributing factor. Here an end‐group modification to a commonly used nonfullerene acceptor (O‐IDTBR) is reported, in which the rhodanine end groups are replaced with dicyano moieties, resulting in the acceptor O‐IDTBCN. This new acceptor affords significant improvement in the fill factor (73%) and photocurrent (19.8 mA cm−2) in organic solar cells with the low bandgap polymer PTB7‐Th. A narrowing of the bandgap, as a result of greater push–pull hybridization, allows complementary absorption to the donor and thus improved photon harvesting. Additionally, the measurement of charge carrier mobilities and lifetimes in both systems reveal that the PTB7‐Th:O‐IDTBCN blend possesses more balanced charge carrier mobilities, and longer lifetimes. Morphology studies reveal a slightly greater degree of molecular mixing of the O‐IDTBCN when blended with PTB7‐Th, despite the greater and more balanced charge carrier mobilities in this blend. [ABSTRACT FROM AUTHOR]

Halide perovskites are known to be photoconductive for more than half a century, and their efficient photocarrier generation gives rise to positive photoconductivity (PPC). In this work, the discovery of negative photoconductivity (NPC) in hybrid perovskite CH3NH3PbBr3 after Bi doping is reported. Transient photoconductivity measurements reveal a surprising bipolar behavior with a fast positive response followed by exponential negative photocurrent decay, resulting in an equilibrium photocurrent even below the dark level. The NPC effect in Bi‐doped CH3NH3PbBr3 is among the largest ones reported so far for semiconductors. It is proposed that the transition to negative photoconductance is related to the presence of DX‐like centers in Bi‐doped halide perovskites, similar to doped III–V and chalcopyrite semiconductors. Such photogenerated DX‐like centers in the Bi‐doped CH3NH3PbBr3 can trap mobile band electrons and enhance charge recombination, thus reducing the conductivity. This mechanism is consistent with the observations of crossover from PPC to NPC as functions of temperature, composition, and illumination. The results underscore the importance of defect engineering for tuning the optoelectronic properties of halide perovskites. [ABSTRACT FROM AUTHOR]

Molecular orientation and π–π stacking of nonfullerene acceptors (NFAs) determine its domain size and purity in bulk‐heterojunction blends with a polymer donor. Two novel NFAs featuring an indacenobis(dithieno[3,2‐b:2ʹ,3ʹ‐d]pyrrol) core with meta‐ or para‐alkoxyphenyl sidechains are designed and denoted as m‐INPOIC or p‐INPOIC, respectively. The impact of the alkoxyl group positioning on molecular orientation and photovoltaic performance of NFAs is revealed through a comparison study with the counterpart (INPIC‐4F) bearing para‐alkylphenyl sidechains. With inward constriction toward the conjugated backbone, m‐INPOIC presents predominant face‐on orientation to promote charge transport. The as‐cast organic solar cells (OSCs) by blending m‐INPOIC and PBDB‐T as active layers exhibit a power conversion efficiency (PCE) of 12.1%. By introducing PC71BM as the solid processing‐aid, the ternary OSCs are further optimized to deliver an impressive PCE of 14.0%, which is among the highest PCEs for as‐cast single‐junction OSCs reported in literature to date. More attractively, PBDB‐T:m‐INPOIC:PC71BM based OSCs exhibit over 11% PCEs even with an active layer thickness over 300 nm. And the devices can retain over 95% of PCE after storage for 20 days. The outstanding tolerance to film thickness and outstanding stability of the as‐cast devices make m‐INPOIC a promising candidate NFA for large‐scale solution‐processable OSCs. [ABSTRACT FROM AUTHOR]

The high crystallinity and ability to harvest near‐infrared photons make diketopyrrolopyrrole (DPP)‐based polymers one of the most promising donors for high performing organic solar cells (OSCs). However, DPP‐based OSC devices still suffer from the trade‐off between energetic loss (Eloss) and maximum external quantum efficiency (EQEmax), which significantly hinders their potential. Thus far, the replacement of fullerenes with small molecule acceptors did not wisdom the performance development of DPP‐donor‐based solar cells due to severe charge recombination issues. In this work, efficient DPP‐based solar cells are reported using low bandgap fused ring electron acceptor, IEICO‐4F. PBDTT‐DPP:IEICO‐4F OSC devices deliver a champion power conversion efficiency of 9.66% with successful interface engineering along with low Eloss of 0.57 eV and a high EQEmax (>70%). [ABSTRACT FROM AUTHOR]

Colloidal quantum dots (CQDs) are attractive materials for thermoelectric applications due to their simple and low‐cost processing; advantageously, they also offer low thermal conductivity and high Seebeck coefficient. To date, the majority of CQD thermoelectric films reported upon have been p‐type, while only a few reports are available on n‐type films. High‐performing n‐ and p‐type films are essential for thermoelectric generators (TEGs) with large output voltage and power. Here, high‐thermoelectric‐performance n‐type CQD films are reported and showcased in high‐performance all‐CQD TEGs. By engineering the electronic coupling in the films, a thorough removal of insulating ligands is achieved and this is combined with excellent surface trap passivation. This enables a high thermoelectric power factor of 24 µW m−1 K−2, superior to previously reported n‐type lead chalcogenide CQD films operating near room temperature (<1 µW m−1 K−2). As a result, an all‐CQD film TEG with a large output voltage of 0.25 V and a power density of 0.63 W m−2 at ∆T = 50 K is demonstrated, which represents an over fourfold enhancement to previously reported p‐type only CQD TEGs. [ABSTRACT FROM AUTHOR]

Novel emerging materials for organic solar cells, such as nonfullerene acceptors, are paving the way for commercialization of organic photovoltaics. Their utilization in unconventional applications, such as conformable and disposable electronics, has turned the focus to inkjet printing as a fabrication method with advantages including low material usage, rapid digital design changes, and high resolution. In this work, the fabrication of efficient nonfullerene acceptor devices through inkjet printing for organic photovoltaic applications is reported for the first time. The engineering of printable poly‐3‐hexylthiophene:rhodanine‐benzothiadiazole‐coupled indacenodithiophene (P3HT:O‐IDTBR) inks is centered on tuning the rheological properties for proper droplet ejection and the selection of solvents, including hydrocarbons, that meet solubility and volatility requirements to avoid common inkjet printing complications like nozzle clogging. The optimization of printing parameters including drop spacing and deposition temperatures results in homogeneous P3HT:O‐IDTBR films with device efficiencies of up to 6.47% for small lab‐scale devices (0.1 cm2), comparable with that of spin‐coating or blade‐coating. A 2 cm2 inkjet‐printed device is also shown to achieve a remarkable efficiency of 6%. To demonstrate their potential usage in customized applications, large‐area devices are fabricated in the shape of a marine turtle with 4.76% efficiency, showcasing the versatility of the inkjet‐printing process for efficient organic photovoltaics. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots (CQDs) are demonstrated to be promising materials to realize high‐performance thermoelectrics owing to their low thermal conductivity. The most studied CQD films, however, are using long ligands that require high processing and operation temperature (>400 °C) to achieve optimum thermoelectric performance. Here the thermoelectric properties of CQD films cross‐linked using short ligands that allow strong inter‐QD coupling are reported. Using the ligands, p‐type thermoelectric solids are demonstrated with a high Seebeck coefficient and power factor of 400 μV K−1 and 30 µW m−1 K−2, respectively, leading to maximum ZT of 0.02 at a lower measurement temperature (<400 K) and lower processing temperature (<300 °C). These ligands further reduce the annealing temperature to 175 °C, significantly increasing the Seebeck coefficient of the CQD films to 580 μV K−1. This high Seebeck coefficient with a superior ZT near room temperature compared to previously reported high temperature‐annealed CQD films is ascribed to the smaller grain size, which enables the retainment of quantum confinement and significantly increases the hole effective mass in the films. This study provides a pathway to approach quantum confinement for achieving a high Seebeck coefficient yet strong inter‐QD coupling, which offers a step toward low‐temperature‐processed high‐performance thermoelectric generators. A strategy to enhance electronic coupling using short ligands that allow lower processing temperature and improved thermoelectric performance in p‐type colloidal quantum dots films is studied. The lower processing temperature is found to increase the Seebeck coefficient and reduce the in‐plane thermal conductivity of the films. Fundamental analysis on grain size, carrier density, and effective mass is highlighted to understand these findings. [ABSTRACT FROM AUTHOR]

Organic–inorganic hybrid materials are of significant interest owing to their diverse applications ranging from photovoltaics and electronics to catalysis. Control over the organic and inorganic components offers flexibility through tuning their chemical and physical properties. Herein, it is reported that a new organic–inorganic hybrid, [Mn(C2H6OS)6]I4, with linear tetraiodide anions exhibit an ultralow thermal conductivity of 0.15 ± 0.01 W m−1 K−1 at room temperature, which is among the lowest values reported for organic–inorganic hybrid materials. Interestingly, the hybrid compound has a unique 0D structure, which extends into 3D supramolecular frameworks through nonclassical hydrogen bonding. Phonon band structure calculations reveal that low group velocities and localization of vibrational energy underlie the observed ultralow thermal conductivity, which could serve as a general principle to design novel thermal management materials. Intriguing physical and chemical properties of a 0D organic–inorganic hybrid crystal lead to unique thermal transport. Ultralow thermal conducti‐vity of 0.15 W m−1 K−1 is recorded for [Mn(C2H6OS)6]I4 owing to its 0D structure and localization of vibrational energy. [ABSTRACT FROM AUTHOR]