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Cyanation is a common chemical modification strategy to fine‐tune the energy levels and molecular packing of organic semiconductors, especially materials used in organic solar cells (OSCs). Generally, cyanation is used to modify the end groups of high‐performance small‐molecule acceptors (SMAs). However, the cyanation strategy has not been investigated on the central backbone of SMAs, which could introduce stronger intermolecular interaction and enhance the π–π stacking for rapid charge transport. This paper, for the first time, reports a new cyanation strategy on the central benzo‐quinoxaline core and synthesizes two novel A‐DA'D‐A type SMAs, named BQx‐CN and BQx‐2CN, with mono‐ and di‐cyanide groups, respectively. Through tailoring the number of CN groups, the BQx‐CN‐based OSC exhibits the best device performance of 18.8%, which is significantly higher than the non‐cyano BQx‐based one. The reason for the superior performance of BQx‐CN‐based devices can be attributed to the fine‐tuned energy level, stronger packing, and ideal phase segregation, which lead to superior exciton dissociation, faster charge transport, and suppressed recombination, therefore the highest fill factor (FF) and power conversion efficiencies (PCE). The research demonstrates the effectiveness of the cyanation strategy on the central core of SMAs for enhanced molecular packing and better performance of OSCs. [ABSTRACT FROM AUTHOR]

Organic solar cell (OSC) development continues to demonstrate impressive device efficiency improvements. However, the materials synthetic simplicity essential to industrialization remains seriously lacking attention, imparting inferior performance records in low‐cost devices. Hence, low bandgap and completely non‐fused electron acceptors (CNFEAs) having simple molecular structures are investigated herein. In contrast to typically explored fused‐ring acceptors with smaller backbone conformational variations, minimizing the interface recombination sites through a greater extent of localized domains is identified as more critical in CNFEAs, leading to remarkable fill factors (FFs) approaching 75%, among the highest currently realized for low‐cost systems. However, this comes with diminishing charge generation efficiency. The general ternary blend optimization strategy modifying the morphology of host components is limited in preserving such remarkably high FFs. To suppress the trade‐off while keeping notable FFs, a new perspective of constructing functionally bridged components based on optical, electronic, and thermodynamic properties is introduced here. Specifically, charge generation is unrestrained from the host acceptor localized domains through the introduction of a "bridge" component while also taking advantage of the configuration to channel polarons toward the efficient transport moieties of the host components. Accordingly, this work incubates understanding‐guided optimizations toward the advancement of more practical devices. [ABSTRACT FROM AUTHOR]

Tuning the properties of non‐fullerene acceptors (NFAs) through halogenation, including fluorination and chlorination, represents one of the most promising strategies to boost the performance of organic solar cells (OSCs). However, it remains unclear how the F and Cl choice influences the molecular packing and performance between small‐molecule and polymeric acceptors. Here, a series of small‐molecule and polymeric acceptors with different amounts and types of halogenation is synthesized, and the effects of fluorination and chlorination between small‐molecule and polymeric acceptors are investigated. It is found that chlorinated small‐molecule acceptors lead to longer exciton diffusion length and better performance compared to the corresponding fluorinated ones, which attributes to their stronger intermolecular packing mode. For polymer acceptors, in contrast, the fluorinated polymers achieve a denser packing mode and better performance, because chlorinated polymers exhibit reduced intrachain conjugation between end group moieties and linker units. This study demonstrates different halogenation effects on the packing modes and performances for small‐molecule and polymeric acceptors, which provides important guidance for the molecule design of high‐performance acceptors for OSCs. [ABSTRACT FROM AUTHOR]

Fullerene acceptors typically possess excellent electron-transporting properties and can work as guest components in ternary organic solar cells to enhance the charge extraction and efficiencies. However, conventional fullerene small molecules typically suffer from undesirable segregation and dimerization, thus limiting their applications in organic solar cells. Herein we report the use of a poly(fullerene-alt-xylene) acceptor (PFBO-C12) as guest component enables a significant efficiency increase from 16.9% for binary cells to 18.0% for ternary all-polymer solar cells. Ultrafast optic and optoelectronic studies unveil that PFBO-C12 can facilitate hole transfer and suppress charge recombination. Morphological investigations show that the ternary blends maintain a favorable morphology with high crystallinity and smaller domain size. Meanwhile, the introduction of PFBO-C12 reduces voltage loss and enables all-polymer solar cells with excellent light stability and mechanical durability in flexible devices. This work demonstrates that introducing polyfullerenes as guest components is an effective approach to achieving highly efficient ternary all-polymer solar cells with good stability and mechanical robustness. Fullerene acceptors typically suffer from undesirable segregation and dimerization. Here, the authors report a poly(fullerene-alt-xylene) acceptor as guest component to facilitate charge transfer and suppress charge recombination, achieving efficiency of 18% for ternary all-polymer solar cells. [ABSTRACT FROM AUTHOR]

Organic solar cells (OSC) feature a hierarchical structure with the electron donor/acceptor layer sandwiched by anode and cathode, which raises the importance of controlling the molecular crystal orientation, domain size, and vertical distribution to facilitate the charge collection at electrodes. However, the similar conjugated backbone of donor/acceptor material and fast film‐formation kinetics have led to spinodal‐decomposition‐orientated phase separation that result in the film presenting an intimately mixed morphology and random molecular orientation. To solve the issue, the mixing Gibbs free energy‐triggered solid–liquid phase separation during the film formation process is enhanced by solidifying one component and solvating the other based on a liquid additive. Following the liquid evaporation process, a favorable vertical distribution is obtained. Meanwhile, the prolonged solvation process enlarges the domain size and assists the molecules to diffuse and orient properly, enabling better exciton/charge dynamics during the power conversion processes. As a result, the fabricated devices exhibit a fill factor over 80% and an efficiency of 18.72%, which is one of the top efficiencies for binary OSCs. Insights and a methodology is provided here to manipulate the organic donor/acceptor phase separation in terms of mixing Gibbs free energy. [ABSTRACT FROM AUTHOR]

Central π‐core engineering of non‐fullerene small molecule acceptors (NF‐SMAs) is effective in boosting the performance of organic solar cells (OSCs). Especially, selenium (Se) functionalization of NF‐SMAs is considered a promising strategy but the structure‐performance relationship remains unclear. Here, we synthesize two isomeric alkylphenyl‐substituted selenopheno[3,2‐b]thiophene‐based NF‐SMAs named mPh4F‐TS and mPh4F‐ST with different substitution positions, and contrast them with the thieno[3,2‐b]thiophene‐based analogue, mPh4F‐TT. When placing Se atoms at the outer positions of the π‐core, mPh4F‐TS shows the most red‐shifted absorption and compact molecular stacking. The PM6 : mPh4F‐TS devices exhibit excellent absorption, high charge carrier mobility, and reduced energy loss. Consequently, PM6 : mPh4F‐TS achieves more balanced photovoltaic parameters and yields an efficiency of 18.05 %, which highlights that precisely manipulating selenium functionalization is a practicable way toward high‐efficiency OSCs. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) are known to be sensitive to the exposure to ambient humidity, which typically results in the degradation and deterioration of performance, although positive effects of exposure to moisture have also been reported, due to recrystallization of the perovskite. Common approach to improve stability is to use 3D/2D perovskite active layer, where 2D capping layer is prepared by spin coating the bulky organic cation halide. Herein, it is shown that optimizing the exposure of the capping layer prepared by spin coating phenylethylammonium iodide (PEAI) to ambient atmosphere results in substantial improvement of the PSC performance. Furthermore, the initial effects of PEAI treatment are dependent on the NiOx/perovskite interface, but in all cases except at very high humidity (80–85% RH) optimized exposure to ambient results in improved performance. The variations in device performance with PEAI treatment and ambient exposure can be attributed to defect passivation and changes in the charge extraction due to energy‐level alignment at the interfaces. The best performing devices have passivation of NiOx/perovskite interface and PEAI treatment of top surface followed by exposure to ambient atmosphere at RH of 40–45%, which results in the power conversion efficiency increase from 20.3% to 22.4%. [ABSTRACT FROM AUTHOR]

Electron donors and acceptors in organic solar cells (OSCs) shall strike a favorable vertical phase separation that acceptors and donors have sufficient contact and gradient accumulation near the cathodes and anodes, respectively. Random mixing of donors/acceptors at surface will result in charge accumulation and severe recombination for low carrier‐mobility organic materials. However, it is challenging to tune the vertical distribution in bulk‐heterojunction films as they are usually made from a well‐mixed donor/acceptor solution. Here, for the first time, it presents with solid evidence that the commonly used 1‐chloronaphthalene (CN) additive can tune the donor/acceptor vertical distribution and establish the mechanism. Different from the previous understanding that ascribed the efficiency enhancement brought by CN to the improved molecular stacking/crystallization, it is revealed that the induced vertical distribution is the dominant factor leading to the significantly increased performance. Importantly, the vertical distribution tunability is effective in various hot nonfullerene OSC systems and creates more channels for the collection of dissociated carriers at corresponding organic/electrode interfaces, which contributes the high efficiency of 18.29%. This study of the material vertical distribution and its correlation with molecular stacking offers methods for additives selection and provides insights for the understanding and construction of high‐performance OSCs. [ABSTRACT FROM AUTHOR]

Chemical modifications of non‐fullerene acceptors (NFAs) play vital roles in the development of high efficiency organic solar cells (OSCs). In this work, on the basis of the previously reported molecule named Y6‐1O, chlorination and inner side‐chain engineering are adopted to endow the corresponding devices with higher open‐circuit voltage (VOC) and short‐circuit current density (JSC) as well as good morphology for high fill factor (FF). As a result, the molecule named BTP1O‐4Cl‐C12 can help achieve a higher power conversion efficiency (PCE) of 17.1% than that of Y6‐1O (16.1%). Furthermore, the following comparisons between BTP1O‐4Cl‐C12 and the two symmetric acceptors named BTP2O‐4Cl‐C12 and BTP‐4Cl‐C12 demonstrate the effect of asymmetric alkoxy substitution on the outer side chains, which not only achieves a balance between VOC and JSC, but also help obtain appropriate morphology for efficient charge dissociation and suppressed charge recombination. Therefore, the asymmetric BTP1O‐4Cl‐C12 can achieve a higher PCE compared to the symmetric BTP2O‐4Cl‐C12 and BTP‐4Cl‐C12. The work not only reports an excellent NFA for high‐performance OSCs, but also puts forward a series of methods for consecutive chemical modifications on Y‐series acceptors, which can be further applied to boost the PCE of OSCs to a higher level. [ABSTRACT FROM AUTHOR]

A solution‐processed top electrode is critical to unlock the full potential of all‐solution‐processed organic solar cells (OSCs) for practical applications. However, the enabled devices suffer from low efficiency (<12%) mainly because of the irreversible damages induced by the top‐electrode deposition process. Herein, a strategy of dry and nonimmersive sintering is demonstrated by introducing a hydrogen‐intercalated molybdenum oxide layer to sinter isolated Ag nanoparticles into the top electrode (all from solution process) with little influences/issues on underlying device structures. Fundamentally, it is unveiled that the intercalated hydrogen will bond with the amino group of the ligands around Ag nanoparticles, which promotes the exposed nanoparticles to merge along a certain crystal orientation (≈45°) and form a conductive electrode (8.6 Ω sq−1). Importantly, the sintered electrode offers 70% optical reflection in the 700–1050 nm wavelength region, which is essential to enhance the light absorption of high‐performance nonfullerene acceptors. Consequently, a record efficiency of 15% is achieved, driving all‐solution processed OSCs toward commercial applications. [ABSTRACT FROM AUTHOR]

Organic solar cells based on nonfullerene acceptor molecules show high charge generation yields with negligible driving force at the donor–acceptor (D/A) interface to drive exciton dissociation. Understanding the underlying charge generation dynamics in these material systems is crucial for further development of this technology. Herein, the acceptor exciton dissociation dynamics in these materials is studied using transient optical spectroscopy. The results show that exciton dissociation at the D/A interface takes up to ≈100 ps to complete, and this process is not significantly affected by temperature. A similar timescale for charge transfer (CT) state separation into free electrons and holes is observed at room temperature. But in contrast to the weak temperature dependence of exciton dissociation, the free charge generation rate and yield are significantly reduced at low temperature. This suggests that overcoming the Coulomb barrier for charge separation at the D/A interface is the main reason for the endothermic charge separation observed for these material systems, instead of diffusion‐limited exciton dissociation. [ABSTRACT FROM AUTHOR]

The discovery of slow hot carrier cooling in hybrid organic–inorganic lead halide perovskites (HOIPs) has provided exciting prospects for efficient solar cells that can overcome the Shockley–Queisser limit. Questions still loom over how electron‐phonon interactions differ from traditional polar semiconductors. Herein, the electron‐phonon coupling (EPC) strength of common perovskite films (MAPbBr3, MAPbI3, CsPbI3, and FAPbBr3) is obtained using transient absorption spectroscopy by analyzing the hot carrier cooling thermodynamics via a simplified two‐temperature model. Density function theory calculations are numerically performed at relevant electron‐temperatures to confirm experiments. Further, the variation of carrier‐temperature over a large range of carrier‐densities in HOIPs is analyzed, and an "S‐shaped" dependence of the initial carrier‐temperature to carrier‐density is reported. The phenomenon is attributed to the dominance of the large polaron screening and the destabilization effect which causes an increasing‐decreasing fluctuation in temperature at low excitation powers; and a hot‐phonon bottleneck which effectively increases the carrier temperature at higher carrier‐densities. The turning point in the relationship is indicative of the critical Mott density related to the nonmetal‐metal transition. The EPC analysis provides a novel perspective to quantify the energy transfer in HOIPs, electron‐lattice subsystem, and the complicated screening‐bottleneck interplay is comprehensively described, resolving the existing experimental contradictions. [ABSTRACT FROM AUTHOR]

As one of the most promising hole‐transporting materials for perovskite solar cells (PSC), NiO is widely used in the inverted p–i–n cell structure due to its high stability, decent hole conductivity, and easy processability for hysteresis‐free cells. However, the efficiency of NiO‐based PSCs is still low, due largely to the poor perovskite/NiO interface. Herein, a sulfur‐doping strategy to modify NiO surface via ion exchange reaction by a simple and scalable chemical bath deposition technique is introduced, which greatly improves the photovoltaic (PV) performance of the derived devices. A systematic investigation is shown where sulfur doping leads to favorable interfacial energetics with a reduced Voc loss. Sulfur doping at the interface also improves the contact between NiO and perovksite and facilitates the formation of high‐quality perovskite films. Carrier dynamics studies demonstrate reduced defect states and trap‐assisted recombination with sulfur doping, which promote the PV performance of the devices. These merits contribute concurrently to low‐loss charge transfer across the perovskite/NiO interface and facilitate charge transport through the perovskite films, leading to a high champion efficiency of 20.43% of the p–i–n structure solar cell devices. [ABSTRACT FROM AUTHOR]

A major challenge for organic solar cell (OSC) research is how to minimize the tradeoff between voltage loss and charge generation. In early 2019, we reported a non-fullerene acceptor (named Y6) that can simultaneously achieve high external quantum efficiency and low voltage loss for OSC. Here, we use a combination of experimental and theoretical modeling to reveal the structure-property-performance relationships of this state-of-the-art OSC system. We find that the distinctive π–π molecular packing of Y6 not only exists in molecular single crystals but also in thin films. Importantly, such molecular packing leads to (i) the formation of delocalized and emissive excitons that enable small non-radiative voltage loss, and (ii) delocalization of electron wavefunctions at donor/acceptor interfaces that significantly reduces the Coulomb attraction between interfacial electron-hole pairs. These properties are critical in enabling highly efficient charge generation in OSC systems with negligible donor-acceptor energy offset. Y6, as a non-fullerene acceptor for organic solar cells, has attracted intensive attention because of the low voltage loss and high charge generation efficiency. Here, Zhang et al. find that the delocalization of exciton and electron wavefunction due to strong π-π packing of Y6 is the key for the high performance. [ABSTRACT FROM AUTHOR]

A nonuniform vertical phase distribution and thick insulating barrier can decrease the energy transfer between slices in layered perovskite solar cells (PSCs). Herein, an interlayer cross‐linked Dion–Jacobson (DJ)‐type 2D PSC with 1,4‐butanediamine (BDA) as a short‐chain insulating spacer [formula: (BDA)MAn −1PbnI3n + 1] is reported and demonstrates the vertical phase becoming uniform with enhanced exciton coupling, leading to reduced nonradiative recombination. For n = 1 pure phase perovskite, an exciton binding energy of the DJ phase (BDA)PbI4 is ≈142 meV, much smaller than ≈435 meV of Ruddlesden–Popper (RP) phase (BA)2PbI4 (n = 1) perovskite, indicative of exciton‐coupling‐induced efficient energy transfer. Therefore, the high energy emission peaks for the (BDA)MA3Pb4I13 film are not observed even in liquid nitrogen temperature (78 K), which can be distinguished from that of the (BA)2MA3Pb4I13 film. Energy transfer between 2D slices of (BDA)MA3Pb4I13 is 100 times faster than that of (BA)2MA3Pb4I13. The uniform vertical distribution and exciton coupling mitigate nonradiative energy loss and significantly improve Voc in inverted structures (PEDOT:PSS/(BDA)MA3Pb4I13/PCBM/bathocuproine/Ag) to ≈1.15 V and the control n‐butylammonium‐based device demonstrates only a Voc = ≈1 V. It is believed that the results would provide a deep understanding of exciton coupling in hybrid multicomponent quantum wells. [ABSTRACT FROM AUTHOR]

Abstract: Hole transport layer (HTL) plays a critical role for achieving high performance solution‐processed optoelectronics including organic electronics. For organic solar cells (OSCs), the inverted structure has been widely adopted to achieve prolonged stability. However, there are limited studies of p‐type effective HTL on top of the organic active layer (hereafter named as top HTL) for inverted OSCs. Currently, p‐type top HTLs are mainly 2D materials, which have an intrinsic vertical conduction limitation and are too thin to function as practical HTL for large area optoelectronic applications. In the present study, a novel self‐assembled quasi‐3D nanocomposite is demonstrated as a p‐type top HTL. Remarkably, the novel HTL achieves ≈15 times enhanced conductivity and ≈16 times extended thickness compared to the 2D counterpart. By applying this novel HTL in inverted OSCs covering fullerene and non‐fullerene systems, device performance is significantly improved. The champion power conversion efficiency reaches 12.13%, which is the highest reported performance of solution processed HTL based inverted OSCs. Furthermore, the stability of OSCs is dramatically enhanced compared with conventional devices. The work contributes to not only evolving the highly stable and large scale OSCs for practical applications but also diversifying the strategies to improve device performance. [ABSTRACT FROM AUTHOR]

Abstract: The effects of alkyl chain regiochemistry on the properties of donor polymers and performances of non‐fullerene organic solar cells are investigated. Two donor polymers (PfBTAZ and PfBTAZS) are compared that have nearly identical chemical structures except for the regiochemistry of alkyl chains. The optical properties and crystallinity of two polymers are nearly identical yet the PfBTAZ:O‐IDTBR blend exhibits nearly double domain size compared to the blend based on PfBTAZS:O‐IDTBR. To reveal the origins of the very different domain size of two blends, the morphology of neat polymer films is characterized, and it is found that PfBTAZ tends to aggregate into much larger polymer fibers without the presence of O‐IDTBR. This indicates that it is not the polymer:O‐IDTBR interactions but the intrinsic aggregation properties of two polymers that determine the morphology features of neat and blend films. The stronger aggregation tendency of PfBTAZ could be explained by its more co‐planar geometry of the polymer backbone arising from the different alkyl chain regiochemistry. Combined with the similar trend observed in another set of donor polymers (PTFB‐P and PTFB‐PS), the results provide an important understanding of the structure–property relationships that could guide the development of donor polymers for non‐fullerene organic solar cells. [ABSTRACT FROM AUTHOR]

The mixed perovskite (FAPbI3)1− x(MAPbBr3) x with methylammonium brodide (MABr)/tert-butanol solution. The converted perovskite thin film shows an optimized absorption edge at 800 nm after reaction time control, and the high crystallinity can be preserved after MABr incorporation. More importantly, it is found that the threshold electrical field to initiate ion migration is greatly increased in DIE perovskite thin film because excess MABr on the surface can effectively heal structural defects located on grain boundaries during the ion exchange process. It contributes to the over-one-month moisture stability under ≈65% room humidity (RH) and greatly enhanced light stability for the bare perovskite film. As a result of preserved high crystallinity and simultaneous grain boundary passivation, the perovskite solar cells fabricated by the DIE method demonstrate reliable reproducibility with an average power conversion efficiency (PCE) of 17% and a maximum PCE of 18.1%, with negligible hysteresis. [ABSTRACT FROM AUTHOR]3 with methylammonium brodide (MABr)/tert-butanol solution. The converted perovskite thin film shows an optimized absorption edge at 800 nm after reaction time control, and the high crystallinity can be preserved after MABr incorporation. More importantly, it is found that the threshold electrical field to initiate ion migration is greatly increased in DIE perovskite thin film because excess MABr on the surface can effectively heal structural defects located on grain boundaries during the ion exchange process. It contributes to the over-one-month moisture stability under ≈65% room humidity (RH) and greatly enhanced light stability for the bare perovskite film. As a result of preserved high crystallinity and simultaneous grain boundary passivation, the perovskite solar cells fabricated by the DIE method demonstrate reliable reproducibility with an average power conversion efficiency (PCE) of 17% and a maximum PCE of 18.1%, with negligible hysteresis. [ABSTRACT FROM AUTHOR]

In article number 1601882, Keyou Yan, Jianbin Xu, and co‐workers report a simple intermediate halide exchange reaction between nonstoichiometric FAI and unstable intermediate HPbI2Br to produce high‐quality FAPbI3‐xBrx thin films with crystal domain up to 2‐3 μm, eliminating the use of antisolvent dripping process. And it demonstrates outstanding opto‐electronic performances as well as enhanced stability under moisture and heat stress. [ABSTRACT FROM AUTHOR]

NiO is a promising hole transporting material for perovskite solar cells due to its high hole mobility, good stability, easy processibility, and suitable Fermi level for hole extraction. However, the efficiency of NiO-based cells is still limited by the slow hole extraction due to the poor perovskite/NiO interface and the inadequate quality of the two solution-processed material phases. Here, large influences of a monolayer surface modification of NiO nanocrystal layers with ethanolamine molecules are demonstrated on the enhancement of hole extraction/transport and thus the photovoltaic performance. The underlying causes have been revealed by a series of studies, pointing to a favorable dipole layer formed by the molecular adsorption along with the enhanced perovskite crystallization and the improved interface contact. Comparatively, the solar cells based on a diethanolamine-modified NiO layer have achieved a rather high fill factor, indeed one of the highest among NiO-based perovskite solar cells, and high short-circuit photocurrent density ( Jsc), resulting in a power conversion efficiency of ≈16%, most importantly, without hysteresis. [ABSTRACT FROM AUTHOR]

The photovoltaic performance of perovskite solar cells (PVSCs) is extremely dependent on the morphology and crystallization of the perovskite film, which is affected by the deposition method. In this work, a new approach is demonstrated for forming the PbI2 nanostructure and the use of high CH3 N3 I concentration which are adopted to form high-quality (smooth and PbI2 residue-free) perovskite film with better photovoltaic performances. On the one hand, self-assembled porous PbI2 is formed by incorporating small amount of rationally chosen additives into the PbI2 precursor solutions, which significantly facilitate the conversion of perovskite without any PbI2 residue. On the other hand, by employing a relatively high CH3NH3 I concentration, a firmly crystallized and uniform CH3NH3 PbI3 film is formed. As a result, a promising power conversion efficiency of 16.21% is achieved in planar-heterojunction PVSCs. Furthermore, it is experimentally demonstrated that the PbI2 residue in perovskite film has a negative effect on the long-term stability of devices. [ABSTRACT FROM AUTHOR]

Organic solar cells based on non-fullerene acceptors can show high charge generation yields despite near-zero donor–acceptor energy offsets to drive charge separation and overcome the mutual Coulomb attraction between electron and hole. Here, we use time-resolved optical spectroscopy to show that free charges in these systems are generated by thermally activated dissociation of interfacial charge-transfer states that occurs over hundreds of picoseconds at room temperature, three orders of magnitude slower than comparable fullerene-based systems. Upon free electron–hole encounters at later times, both charge-transfer states and emissive excitons are regenerated, thus setting up an equilibrium between excitons, charge-transfer states and free charges. Our results suggest that the formation of long-lived and disorder-free charge-transfer states in these systems enables them to operate closely to quasi-thermodynamic conditions with no requirement for energy offsets to drive interfacial charge separation and achieve suppressed non-radiative recombination. Designing efficient organic solar cells is limited by the energy required to overcome the mutual Coulomb attraction between electron and hole. Here, the authors reveal long-lived and disorder-free charge-transfer states enable efficient endothermic charge separation in non-fullerene systems with marginal energy offset. [ABSTRACT FROM AUTHOR]

The hole transport material (HTM) free carbon based perovskite solar cells (C‐PSCs) are promising for its manufactural simplicity, but they currently suffer from low power conversion efficiencies (PCE) largely because of the voltage loss. Here, a new strategy to increase the PCE by incorporating an ultrathin ferroelectric oxide PbTiO3 layer between the electron transport material and the halide perovskite is reported. The resulting C‐PSCs have achieved PCEs up to 16.37%, which is the highest record for HTM‐free C‐PSCs to date, mainly ascribable to the ferroelectric layer enhanced open circuit voltage. Detail measurements and analysis show an enhanced built‐in potential in the C‐PSCs as well as suppression of the non‐radiative recombination due to the ferroelectric PbTiO3 layer incorporation, accounting for the boosted VOC and photovoltaic performance. An ultrathin ferroelectric oxide PbTiO3 layer is incorporated between the electron transport material and the halide perovskite in the hole transport material (HTM) free carbon‐based perovskite solar cell (C‐PSCs). The achieved power conversion efficiency is as high as 16.37%, which is the highest record for HTM‐free C‐PSCs to date, mainly ascribable to the ferroelectric layer enhanced open circuit voltage. [ABSTRACT FROM AUTHOR]