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We develop a new series of ionic liquids with dual functionality as a dopant for hole transport materials and a passivator for perovskite surfaces, which enables the production of large-area solar modules with efficiencies approaching 20%.

Despite the outstanding role of conjugated polyelectrolytes (CPEs) in organic solar cells, the use of CPEs in perovskite solar cells has rarely been reported due to instability issues of the material itself under operating conditions.

In perovskite solar cells, doped organic semiconductors are often used as charge-extraction interlayers situated between the photoactive layer and the electrodes. The π-conjugated small molecule 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9-spirobifluorene (spiro-OMeTAD) is the most frequently used semiconductor in the hole-conducting layer1-6, and its electrical properties considerably affect the charge collection efficiencies of the solar cell7. To enhance the electrical conductivity of spiro-OMeTAD, lithium bis(trifluoromethane)sulfonimide (LiTFSI) is typically used in a doping process, which is conventionally initiated by exposing spiro-OMeTAD:LiTFSI blend films to air and light for several hours. This process, in which oxygen acts as the p-type dopant8-11, is time-intensive and largely depends on ambient conditions, and thus hinders the commercialization of perovskite solar cells. Here we report a fast and reproducible doping method that involves bubbling a spiro-OMeTAD:LiTFSI solution with CO2 under ultraviolet light. CO2 obtains electrons from photoexcited spiro-OMeTAD, rapidly promoting its p-type doping and resulting in the precipitation of carbonates. The CO2-treated interlayer exhibits approximately 100 times higher conductivity than a pristine film while realizing stable, high-efficiency perovskite solar cells without any post-treatments. We also show that this method can be used to dope π-conjugated polymers.

The hole-transporting layer is an essential component in a perovskite solar cell (PSC) and plays a key role in controlling both power conversion efficiency (PCE) and stability. Here, we report a ne...

Despite huge improvements in power conversion efficiencies of perovskite solar cells, the technology is still limited by fill factors at around 80%. Here, we report perovskite solar cells having ex...

To extract charges more efficiently through charge-transporting layers (CTLs), various dopants are necessary. Lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) is the most widely used dopant in ...

Despite the promise of simple manufacturing via an entirely solution-based process at low temperature (

‘Sol–gel’-processed transition metal oxide (TMO) thin films sandwiched by an organic photoactive layer and metal electrodes have proven to be a versatile interlayer for photovoltaics with long-term stability on the laboratory scale; however, chemical defects and dewetting (or shrinkage) processes during sol–gel synthesis on top of the photoactive layer often cause performance variations, impeding the development of large-area photovoltaic modules. Here, we demonstrate that a low surface energy difference at the organic interface allows long-range diffusion of metal ion precursors to promote continuous chemical synthesis associated with oxo-bridge formation. Using high-resolution Auger electron spectroscopy, we confirm that the resultant TMO thin film on top of the suitable surface has a defect-free and continuous metal–oxygen network (MON) with a high oxygen/metal ratio. Our findings can be applied to obtain organic/perovskite photovoltaic modules having long-term stability, approaching an efficiency of 4.2%/14.5% and maintaining over 80% of their initial efficiency for up to 1500 hours/2000 hours with an area of 10.8 cm2/9.06 cm2.

Printable organic sensors fabricated from solution-processed π-conjugated polymers (π-CPs) are promising candidates to detect volatile organic compounds (VOCs) due to the intriguing physical, chemical and electronic properties of π-CPs. These devices, often termed organic chemiresistors, require good sensing capabilities to transduce stimuli from specific VOCs at low concentrations into analytical electric signals. However, discriminating such VOCs using organic chemiresistors has proven very challenging. Herein, we report that the molecular-level electrochemical doping of π-CPs with solid-state ionic liquids (SILs) significantly improves their electrical conductivity (∼10−1 S cm−1) and selective VOC interactions, which can be manipulated through different π-CPs:SIL blend ratios. These characteristics enable the fine discrimination of VOCs at concentrations in the parts-per-billion (ppb) range under low power consumption (

Correction for ‘Conjugated polyelectrolytes for stable perovskite solar cells based on methylammonium lead triiodide’ by Yong Ryun Kim et al., J. Mater. Chem. A, 2022, 10, 3321–3329, https://doi.org/10.1039/D1TA10185D.

This report addresses indium oxide doped with titanium and tantulum with high near-infrared transparency to potentially replace the conventional indium tin oxide transparent electrode used in semitransparent perovskite devices and top cells of tandem devices. The high near-infrared transparency of this electrode is possibly explained by the lower carrier concentration, suggesting less defect sites that may sacrifice its optical transparency. Incorporating this transparent electrode into semitransparent perovskite solar cells for both the top and bottom electrodes improved the device performance through possible reduction of interfacial defect sites and modification in energy alignment. With this indium oxide-based semitransparent perovskite top cell, we also demonstrated four-terminal perovskite-silicon tandem configurations with improved photocurrent response in the bottom silicon cell.

Summary For commercializing perovskite solar cells (PSCs), moisture-tolerant materials are required because a moisture-free environment cannot be maintained on an actual production line (large scale). Recently, PSCs with efficiency exceeding 22% have been fabricated using Li-doped mesoporous TiO2 as an electron transport layer (ETL). However, the use of Li can negatively influence device stability during the fabrication process under humid air because of its hydroscopic property. Here, we report a strategy for improving processing stability without sacrificing the power conversion efficiency (PCE) under a humid atmospheric environment by employing a mesoporous BaSnO3 as an ETL. Using the mesoporous BSO ETL, we achieved a certified efficiency of 21.3% and stabilized efficiency of 21.7%. Furthermore, the BSO-based PSCs also exhibited better processing stability than Li-doped TiO2-based PSCs under humid air. We believe that this strategy of introducing BSO into PSCs will accelerate the commercialization of PSCs.

Perovskite solar cells in an n-i-p structure record high power conversion efficiency, but issues of insufficient thermal stability and the high cost of p-type hole transporting materials have been raised as drawbacks. H

In perovskite solar cells, doped organic semiconductors are often used as charge-extraction interlayers situated between the photoactive layer and the electrodes. The π-conjugated small molecule 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9-spirobifluorene (spiro-OMeTAD) is the most frequently used semiconductor in the hole-conducting layer

Perovskite solar cells (PSCs) require both high efficiency and good long-term stability if they are to be commercialized. It is crucial to finely optimize the energy level matching between the perovskites and hole-transporting materials to achieve better performance. Here, we synthesize a fluorene-terminated hole-transporting material with a fine-tuned energy level and a high glass transition temperature to ensure highly efficient and thermally stable PSCs. We use this material to fabricate photovoltaic devices with 23.2% efficiency (under reverse scanning) with a steady-state efficiency of 22.85% for small-area (~0.094 cm2) cells and 21.7% efficiency (under reverse scanning) for large-area (~1 cm2) cells. We also achieve certified efficiencies of 22.6% (small-area cells, ~0.094 cm2) and 20.9% (large-area, ~1 cm2). The resultant device shows better thermal stability than the device with spiro-OMeTAD, maintaining almost 95% of its initial performance for more than 500 h after thermal annealing at 60 °C. Interfacial losses between device layers play a key role in determining characteristics of solar cells. Jeon et al. address this in perovskite solar cells by synthesizing a hole-transporting layer that is better matched to the surrounding layers, and show high-efficiency and high-stability devices.

Elimination of charge trapping at defects is highly challenging for poly-crystalline organometal halide perovskites. Here, we report a new architecture for reinforcing the built-in electric field (Ein) across the photoactive layer with a pair of strong electric dipole layers (EDLs). The paired EDLs significantly intensify the Ein across the perovskite layer, resulting in suppressed charge trapping of photogenerated charges. As a result, our low-temperature processed P–I–N planar PeSC devices using the paired EDLs exhibit a higher power conversion efficiency (ηmax ∼ 19.4%) and a smaller device-to-device variation with a standard deviation (S.D.) of 0.70%, which far surpass those (ηmax ∼ 17.8%, S.D. ∼ 1.1%) of the devices with typical charge transport layers.

Stretchable conductive materials have received great attention owing to their potential for realizing next-generation stretchable electronics. However, the simultaneous achievement of excellent mechanical stretchability and high electrical conductivity as well as cost-effective fabrication has been a significant challenge. Here, we report a highly stretchable and highly conducting polymer that was obtained by incorporating an ionic liquid. When 1-ethyl-3-methylimidazolium tetracyanoborate (EMIM TCB) was added to an aqueous conducting polymer solution of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), it was found that EMIM TCB acts not only as a secondary dopant but also as a plasticizer for PEDOT:PSS, resulting in a high conductivity of >1000 S cm–1 with stable performance at tensile strains up to 50% and even up to 180% in combination with the prestrained substrate technique. Consequently, by exploiting the additional benefits of high transparency and solution-processability of PEDO...

We investigate a correlation between the type of solvent additives (SAs) with specific criteria such as aromatic additives (AAs) and non-aromatic additives (NAAs) and phase separation in the bulk heterojunction (BHJ) films comprising low-band gap polymer and fullerene derivatives. When AAs are used as SAs, the geometrical structures (π-π and lamellar stacking) of aggregated polymer chains do not significantly change. However, NAAs increase the lamellar stacking distance through a strong interaction with non-aromatic segments of polymers. Therefore, a well-phase separated BHJ morphology with the finer fibrils is developed, thereby leading to balanced charge mobilities and a reduced charge recombination in BHJ solar cells. Finally, the optimized solar cell exhibits a high power conversion efficiency of 7.9%.

Ionic defects (e.g., organic cations and halide anions), preferably residing along grain boundaries (GBs) and on perovskite film surfaces, are known to be a major source of the notorious environmental instability of perovskite solar cells (PeSCs). Although passivating ionic defects is desirable, previous approaches using Lewis base or acid molecules as additives suppress only the negatively or positively charged defects, thus leaving oppositely charged defects. In this work, both the cationic and anionic defects inside methyl ammonium lead tri-iodide (MAPbI3 ) are simultaneously passivated by introducing a zwitterionic form of the amino acid, L-alanine, into the precursor solution as an additive. L-alanine has both positive (NH3 + ) and negative (COO- ) functional groups at a specific solvent pH, thereby passivating both the cation and anion defects in MAPbI3 . The addition of L-alanine increases the grain size of the perovskite crystals and lengthens the charge carrier lifetime (τ > 1 µs), leading to improved power conversion efficiencies (PCEs) of 20.3% (from 18.3% without an additive) for small-area (4.64 mm2 ) devices and 15.6% (from 13.5%) for large-area submodules (9.06 cm2 ). More importantly, the authors' approach also significantly enhances the shelf storage and photoirradiation stabilities of PeSCs.

Recently, the most efficient tandem polymer solar cells (PSCs) have used poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PSS) as a p-type component of recombination layer (RL). However, its undesirable acidic nature, originating from insulating PSS, ofPSS drastically reduces the lifetime of PSCs. Here, we demonstrate the efficient and stable tandem PSCs by introducing acid-free self-doped conducting polymer (SCP), combined with zinc oxide nanoparticles (ZnO NPs), as RL forPSS-free tandem PSCs. Moreover, we introduce an innovative and versatile nanocomposite system containing photoactive and p-type conjugated polyelectrolyte (p-CPE) into the tandem fabrication of an ideal self-organized recombination layer. In our new RL, highly conductive SCP facilitates charge transport and recombination process, and p-CPE helps to achieve nearly loss-free charge collection by increasing effective work function of indium tin oxide (ITO) and SCP. Because of the synergistic effect of extremely low electrical resistance, ohmic contact, and pH neutrality, tandem devices with our novel RL performed well, exhibiting a high power conversion efficiency of 10.2% and a prolonged lifetime. These findings provide a new insight for strategic design of RLs using SCPs to achieve efficient and stable tandem PSCs and enable us to review and extend the usefulness of SCPs in various electronics research fields.

Despite recent reports of high power conversion efficiency (PCE) values of over 20%, the instability of perovskite solar cells (PSCs) has been considered the most serious obstacle toward their commercialization. By rigorously exploring the self-degradation process of planar-type PSCs using typical metal electrodes (Ag or Al), we found that the corrosion of the metal electrodes by inherent ionic defects in the perovskite layers is a major origin of intrinsic device degradation even under inert conditions. In this work, we have developed a new concept of a chemical inhibition in PSCs using amine-mediated metal oxide systems and succeeded in chemically neutralizing mobile ionic defects through mutual ionic interaction. As a consequence, we realized planar-type PSCs with long-term stability that maintain nearly 80% of their initial PCEs even after 1 year (9000 h) of storage under nitrogen and 80% of their initial PCEs after 200 h in ambient conditions without any encapsulation.

Efficient large-area planar heterojunction (PHJ) perovskite solar cells (PSCs) were successfully developed by adapting a scalable doctor blade printing method under ambient condition. To achieve high-quality perovskite films onto poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) layer, the PEDOT:PSS was modified by adding poly(4-styrenesulfonic acid) (PSSH), which uses the electrostatic interaction between the sulfonyl functional groups in PEDOT:PSS and perovskite precursor ions. The resulting perovskite film on the modified PEDOT:PSS (M-PEDOT:PSS) exhibited excellent uniformity and surface coverage with high crystallinity even for large-area (15 mm×40 mm) scale. In addition, the power conversion efficiency (PCE) of the printed PSCs was significantly improved from 6% to 10.15% by introducing our M-PEDOT:PSS layer. This finding provides an important guideline to achieve highly efficient PSCs using scalable printing techniques.

The fabrication of organic photovoltaic modules via printing techniques has been the greatest challenge for their commercial manufacture. Current module architecture, which is based on a monolithic geometry consisting of serially interconnecting stripe-patterned subcells with finite widths, requires highly sophisticated patterning processes that significantly increase the complexity of printing production lines and cause serious reductions in module efficiency due to so-called aperture loss in series connection regions. Herein we demonstrate an innovative module structure that can simultaneously reduce both patterning processes and aperture loss. By using a charge recombination feature that occurs at contacts between electron- and hole-transport layers, we devise a series connection method that facilitates module fabrication without patterning the charge transport layers. With the successive deposition of component layers using slot-die and doctor-blade printing techniques, we achieve a high module efficiency reaching 7.5% with area of 4.15 cm2., The fabrication of organic photovoltaic modules usually relies on patterning techniques which limit their efficiencies. Here, the authors propose a module structure that avoids the patterning steps, and use doctor-blade printing and slot-die coating to fabricate large-area modules reaching 7.5% efficiencies.

We devised an electrochemical patterning process for large-area perovskite photovoltaic modules., Realizing industrial-scale, large-area photovoltaic modules without any considerable performance losses compared with the performance of laboratory-scale, small-area perovskite solar cells (PSCs) has been a challenge for practical applications of PSCs. Highly sophisticated patterning processes for achieving series connections, typically fabricated using printing or laser-scribing techniques, cause unexpected efficiency drops and require complicated manufacturing processes. We successfully fabricated high-efficiency, large-area PSC modules using a new electrochemical patterning process. The intrinsic ion-conducting features of perovskites enabled us to create metal-filamentary nanoelectrodes to facilitate the monolithic serial interconnections of PSC modules. By fabricating planar-type PSC modules through low-temperature annealing and all-solution processing, we demonstrated a notably high module efficiency of 14.0% for a total area of 9.06 cm2 with a high geometric fill factor of 94.1%.

Processing additives have been widely utilized for high-performance organic bulk-heterojunction (BHJ) photovoltaic devices. However, the role of processing additives remained unclear due to the limited information relying on the final BHJ film state rather than the intermediate film state during solvent evaporation. Here, by using in situ GIWAXS measurements on the intermediate BHJ film, we propose a possible phase separation mechanism in efficient BHJ solar cells consisting of a narrow band gap polymer (P1) and PC71BM via the use of 1-chloronaphthalene (1-CN) as a processing additive. We found that adding small amounts of an additive, 1-CN, with a high boiling point and a high PC71BM solubility can prolong the solvent evaporation time and dissolve many PC71BM molecules, promoting the strong P1 polymer:solvent and PC71BM:solvent interaction to produce pure domains of each component. Thus, the bi-continuous networks for both P1 and PC71BM and their enlarged interfacial area are well fabricated in the BHJ films, inducing balanced photo-charge carrier densities for the electrons and holes and improving the overall photovoltaic performance. Therefore, our findings elucidate the kinetic motions of two organic phases affected by the physical properties of the solvents in the process of film formation and establish criteria for BHJ systems.

A new tandem architecture for printable photovoltaics using a versatile organic nanocomposite containing photoactive and interfacial materials is demonstrated. The nanocomposite forms an ideal self-organized recombination layer via a spontaneous vertical phase separation, which yields a simplified tandem structure fabricated with only four component layers and a high tandem efficiency of 10.8%.

Organic semiconductors are key building blocks for future electronic devices that require unprecedented properties of low-weight, flexibility, and portability. However, the low charge-carrier mobility and undesirable processing conditions limit their compatibility with low-cost, flexible, and printable electronics. Here, we present significantly enhanced field-effect mobility (μ(FET)) in semiconducting polymers mixed with boron-doped carbon nanotubes (B-CNTs). In contrast to undoped CNTs, which tend to form undesired aggregates, the B-CNTs exhibit an excellent dispersion in conjugated polymer matrices and improve the charge transport between polymer chains. Consequently, the B-CNT-mixed semiconducting polymers enable the fabrication of high-performance FETs on plastic substrates via a solution process; the μFET of the resulting FETs reaches 7.2 cm(2) V(-1) s(-1), which is the highest value reported for a flexible FET based on a semiconducting polymer. Our approach is applicable to various semiconducting polymers without any additional undesirable processing treatments, indicating its versatility, universality, and potential for high-performance printable electronics.

The importance of interfacial engineering as a new strategy for improving the power conversion efficiencies (PCEs) of planar-heterojunction (PHJ) perovskite solar cells is highlighted in this study. With our optimized interfacial modification, we demonstrated efficient PHJ perovskite solar cells with a high PCE of 12.2% using a sol–gel-processed ZnO ECL modified by [6,6]-phenyl C61 butyric acid methyl ester (PCBM).

Simultaneously achieving high optical transparency and excellent charge mobility in semiconducting polymers has presented a challenge for the application of these materials in future "flexible" and "transparent" electronics (FTEs). Here, by blending only a small amount (∼15 wt %) of a diketopyrrolopyrrole-based semiconducting polymer (DPP2T) into an inert polystyrene (PS) matrix, we introduce a polymer blend system that demonstrates both high field-effect transistor (FET) mobility and excellent optical transparency that approaches 100%. We discover that in a PS matrix, DPP2T forms a web-like, continuously connected nanonetwork that spreads throughout the thin film and provides highly efficient 2D charge pathways through extended intrachain conjugation. The remarkable physical properties achieved using our approach enable us to develop prototype high-performance FTE devices, including colorless all-polymer FET arrays and fully transparent FET-integrated polymer light-emitting diodes.

Despite the excellent work function adjustability of conjugated polyelectrolytes (CPEs), which induce a vacuum level shift via the formation of permanent dipoles at the CPE/metal electrode interface, the exact mechanism of electron injection through the CPE electron transport layer (ETL) remains unclear. In particular, understanding the ionic motion within the CPE ETLs when overcoming the sizable injection barrier is a significant challenge. Because the ionic functionality of CPEs is a key component for such functions, a rigorous analysis using highly controlled ion density (ID) in CPEs is crucial for understanding the underlying mechanism. Here, by introducing a new series of CPEs with various numbers of ionic functionalities, energy level tuning at such an interface can be determined directly by adjusting the ID in the CPEs. More importantly, these series CPEs indicate that two different mechanisms must be invoked according to the CPE thickness. The formation of permanent interfacial dipoles is critical with respect to electron injection through CPE ETL (≤ 10 nm, quantum mechanical tunneling limit), whereas electron injection through thick CPE ETL (20–30 nm) is dominated by the reorientation of the ionic side chains under a given electric field.

The most effi cient class of polymer materials (as donors) follows a push-pull molecular design that utilizes internal charge transfer (ICT) from electron-rich units to electron-defi cient moieties within the fundamental repeating unit of π -conjugated polymers ( π -CPs). [ 4–6 ] However, when push-pull π -CP donors form composites with fullerene acceptors to create BHJ active layers, undesirable phase segregation between the two components is observed on the scale of a few hundred nanometers. Because large-scale phase segregation increases the probability of exciton (electron-hole pair) recombination in the BHJ active layer due to the relatively short diffusion length of the exciton in the polymers (approximately 20 nm), [ 7 ] the PCE is drastically reduced in BHJ solar cells with large-scale phase segregation. [ 8,9 ]

We demonstrate high-performance polymer tandem devices (PTDs) combining solar cell (SC) and light-emitting diode (LED), which are fabricated using solution-based techniques for each layer with the use of semiconducting and metallic polymers. The PTD has three terminals—two outer electrodes and an internal common electrode—and functions as a SC and a LED. In the SC mode, the PTD exhibits a reasonable power conversion efficiency of 3.1% under AM 1.5 irradiation conditions, whereas the device functions as a LED with a luminance of 8000 cd/m 2 when applying external bias voltages. A sol–gel processed titanium sub-oxide (TiO x ) is efficiently used in the PTDs for carrier transport toward the target electrode.

The past two decades of vigorous interdisciplinary approaches has seen tremendous breakthroughs in both scientific and technological developments of bulk-heterojunction organic solar cells (OSCs) based on nanocomposites of π-conjugated organic semiconductors. Because of their unique functionalities, the OSC field is expected to enable innovative photovoltaic applications that can be difficult to achieve using traditional inorganic solar cells: OSCs are printable, portable, wearable, disposable, biocompatible, and attachable to curved surfaces. The ultimate objective of this field is to develop cost-effective, stable, and high-performance photovoltaic modules fabricated on large-area flexible plastic substrates via high-volume/throughput roll-to-roll printing processing and thus achieve the practical implementation of OSCs. Recently, intensive research efforts into the development of organic materials, processing techniques, interface engineering, and device architectures have led to a remarkable improvement in power conversion efficiencies, exceeding 11%, which has finally brought OSCs close to commercialization. Current research interests are expanding from academic to industrial viewpoints to improve device stability and compatibility with large-scale printing processes, which must be addressed to realize viable applications. Here, both academic and industrial issues are reviewed by highlighting historically monumental research results and recent state-of-the-art progress in OSCs. Moreover, perspectives on five core technologies that affect the realization of the practical use of OSCs are presented, including device efficiency, device stability, flexible and transparent electrodes, module designs, and printing techniques.

Electro-spray (e-spray) is emerging as an attractive printing method for the thin-film fabrication of organic materials because of the simple apparatus and its high efficiency. Here, we demonstrate a fully e-sprayed organic solar cell (OSC) with high performance by using an additive in the poly(3-hexylthiophene):[6,6]-phenyl C 61 -butyric acid methyl ester (P3HT:PCBM) layer without any post-processing treatment. The P3HT:PCBM film fabricated with 6 vol% 1,8-diiodooctane (DIO) showed improved surface macro- and nano-morphologies, which resulted in an enhanced photovoltaic performance. Using optimized conditions, we obtained a 2.98% efficient OSC (as-prepared condition) with the e-spray method, and post-annealing increased the power conversion efficiency (PCE) slightly to 3.08%.

The advantage of dimethyl-2 H -benzimidazole compared to the benzothiadiazole moiety of PCDTBT is to improve the solubility of the polymer while keeping the 1,2-quinoid form to lead coplanarity of the backbone. New random copolymers, to broaden the absorption range for the wider coverage of the solar spectrum, were synthesized by Stille coupling reactions to generate PCPPDTMBIs (or PCPPBBTMBIs). The solid films of PCPPDTMBIs show absorption bands with two maximum peaks at about 408–417 and 613–640 nm. The PCPPBBTMBIs show two maxima peaks at about 440–444 and 627–650 nm which are red-shifted about 5–30 nm as compared to PCPPDTMBIs caused by the introduction of bithiophene units. The device with PCPPBBTMBI7:PC 71 BM blend demonstrated a V OC value of 0.64 V, a J SC value of 2.12 mA/cm 2 , and a FF of 0.34, leading to the efficiency of 0.46%.