Chen Weijie

Perovskite solar cells fabricated on aluminum‐doped zinc oxide (AZO)/quartz substrates are shown with a record efficiency of 15%, and their radiation hardness to 150 keV protons is presented. The cells show robust stability up to 10¹³ protons cm⁻², with degradation at 10¹⁴ and 10¹⁵ protons ccm⁻². Transient photovoltage measurements show an increase in minority carrier density and lifetime from 10¹² protons cm⁻².

Perovskite solar cells (PSCs) have gained increasing interest for space applications. However, before they can be deployed into space, their resistance to ionizing radiations, such as high‐energy protons, must be demonstrated. Herein, the effect of 150 keV protons on the performance of PSCs based on aluminum‐doped zinc oxide (AZO) transparent conducting oxide (TCO) is investigated. A record power conversion efficiency of 15% and 13.6% is obtained for cells based on AZO under AM1.5G and AM0 illumination, respectively. It is demonstrated that PSCs can withstand proton irradiation up to 10¹³ protons cm⁻² without significant loss in efficiency. From 10¹⁴ protons cm⁻², a decrease in short‐circuit current of PSCs is observed, which is consistent with interfacial degradation due to deterioration of the Spiro‐OMeTAD holes transport layer during proton irradiation. The structural and optical properties of perovskite remain intact up to high fluence levels. Although shallow trap states are induced by proton irradiation in perovskite bulk at low fluence levels, charges are released efficiently and are not detrimental to the cell's performance. This work highlights the potential of PSCs based on AZO TCO to be used for space applications and gives a deeper understanding of interfacial degradation due to proton irradiation.

A general method is developed to synthesize four ternary metal oxides (TMO) with the idea of a proposed concept of constructing the hypocrystalline hydroxide intermediate. An example of the potential applications for the prepared TMOs is demonstrated by using TMO as the hole transport layer for organic solar cell and perovskite solar cells.

Abstract

Solution‐process fine metal‐oxide nanoparticles are promising carrier transport layer candidates for unlocking the full potential of solution process in solar cells, due to their low cost, good stability, and favorable electrical/optical properties. However, exotic organic ligands adopted for achieving small size and monodispersion can mostly cause poor conductivity, which thus impedes their electrical application. In this work, a concept of constructing a hypocrystalline intermediate is proposed to develop a general method for synthesizing various ternary metal oxide (TMO) nanoparticles with a sub‐ten‐nanometer size and good dispersibility without exotic ligands. Particularly, a guideline is summarized based on the understandings about the impact of metal ion intercalation as well as water and anion coordination on the hypocrystalline intermediate. A general method based on the proposed concept is developed to successfully synthesize various sub‐ten‐nanometer TMO nanoparticles with excellent ability for forming high‐quality (smooth and well‐coverage) films. As an application example, the high‐quality films are used as hole transport layers for achieving high‐performance (stability and efficiency) organic/perovskite solar cells. Consequently, this work will contribute to the development of TMO for large‐scale and high‐performance optoelectronic devices and the concept of tailoring intermediate can leverage the fundamental understandings of synthesis strategies for other metal oxides.

A series of wide bandgap donor polymers are designed and synthesized by incorporating a monothiophene functionalized with both a fluorine atom and an ester group. Fabricated from nonhalogenated solvent, power conversion efficiencies of 11.39% and 12.11% are achieved for binary and ternary nonfullerene solar cells, respectively.

Abstract

Significant progress has been made in nonfullerene small molecule acceptors (NF‐SMAs) that leads to a consistent increase of power conversion efficiency (PCE) of nonfullerene organic solar cells (NF‐OSCs). To achieve better compatibility with high‐performance NF‐SMAs, the direction of molecular design for donor polymers is toward wide bandgap (WBG), tailored properties, and preferentially ecofriendly processability for device fabrication. Here, a weak acceptor unit, methyl 2,5‐dibromo‐4‐fluorothiophene‐3‐carboxylate (FE‐T), is synthesized and copolymerized with benzo[1,2‐b:4,5‐b′]dithiophene (BDT) to afford a series of nonhalogenated solvent processable WBG polymers P1‐P3 with a distinct side chain on FE‐T. The incorporation of FE‐T leads to polymers with a deep highest occupied molecular orbital (HOMO) level of −5.60−5.70 eV, a complementary absorption to NF‐SMAs, and a planar molecular conformation. When combined with the narrow bandgap acceptor ITIC‐Th, the solar cell based on P1 with the shortest methyl chain on FE‐T achieves a PCE of 11.39% with a large V _oc of 1.01 V and a J _sc of 17.89 mA cm⁻². Moreover, a PCE of 12.11% is attained for ternary cells based on WBG P1, narrow bandgap PTB7‐Th, and acceptor IEICO‐4F. These results demonstrate that the new FE‐T is a highly promising acceptor unit to construct WBG polymers for efficient NF‐OSCs.

A power conversion efficiency of 13.36% in ternary organic photovoltaics is obtained by carefully picking materials with good compatibility and complementary absorption spectra, as well as well‐matched energy levels with efficient energy transfer.

Abstract

Organic photovoltaics (OPVs) are fabricated with PM6 as donor and T6Me, IT‐2F, or their mixture as acceptor. A 13.36% power conversion efficiency (PCE) is achieved from the optimized ternary OPVs with 50 wt% IT‐2F in acceptors, which is attributed to the enhanced photon harvesting of ternary active layers and improved exciton utilization efficiency through energy transfer from IT‐2F to T6Me. The efficient energy transfer from IT‐2F to T6Me can be confirmed from the photoluminescence spectra of neat and blend films, which may provide additional channels to enhance exciton utilization efficiency for achieving short‐circuit current density (J _SC) improvement of ternary OPVs. It should be highlighted that the fill factor (FF) of ternary OPVs can be monotonously increased along with the incorporation of IT‐2F, indicating the gradually optimized phase separation degree of ternary active layers. The third component IT‐2F plays a key role in optimizing phase separation as a morphology regulator. Over 8% PCE improvement is achieved in the optimized ternary OPVs compared with the over 12% PCEs of the corresponding binary OPVs, respectively. This work indicates that the performance of ternary OPVs can be well optimized by carefully picking materials with good compatibility and complementary absorption spectra, as well as the appropriate energy levels.

Publication date: November 2019

Source: Nano Energy, Volume 65

Author(s): In Young Choi, Chan Ul Kim, Wonjin Park, Hyungmin Lee, Myoung Hoon Song, Kuen Kee Hong, Sang Il Seok, Kyoung Jin Choi

Graphical abstract

The interface and bulk defects of perovskite solar cells are distinguished and quantified, and are for the first time traced in situ using an expanded admittance model. A fullerene derivative [6, 6]‐phenyl‐C61‐butyric acid (PCBA) is introduced into the TiO₂/perovskite interface to release the interface stress.

Abstract

The stability issue that is obstructing commercialization of the perovskite solar cell is widely recognized, and tremendous effort has been dedicated to solving this issue. However, beyond the apparent thermal and moisture stability, more intrinsic semiconductor mechanisms regarding defect behavior have yet to be explored and understood. Herein, defects are quantified; especially interface defects, within the cell to reveal their impact on device performance and especially stability. Both the bulk and interface defects are distinguished and traced in situ using an expanded admittance model when the cell degrades in its efficiency under illumination or voltage. The electric field‐induced interface, rather than bulk defects, is found to have a direct correlation to stability. Releasing the interface strain using a fullerene derivative is an effective way to suppress interface defect formation and improve stability. Overall, this work provides a quantitative approach to probing the semiconductor mechanism behind the stability issue, and the inherent correlation discovered here among the electric field, interface strain, interface defects, and cell stability has important implications for ongoing device stability engineering.

2D materials have shown great potential for use as photovoltaic materials owing to their outstanding properties. The application of a wide variety of emerging 2D materials for efficient, scalable, and stable perovskite solar cells is reviewed. Interface engineering, energy level alignment, film morphology control, instability issues, hysteresis phenomena, and other key factors are discussed.

Abstract

Perovskite solar cells (PSCs) are now at the forefront of the state‐of‐the‐art photovoltaic technologies due to their high efficiency and low fabrication costs. To further realize the potential of this fascinating class of solar cells, nanostructured functional materials have been playing important roles. 2D layered materials have attracted a great deal of interest due to their fascinating properties and unique structure. Recently, the exploration of a wide range of novel 2D materials for use in PSCs has seen considerable progress, but still a lot remains to be done in this field. In this progress report, the advancements that have recently been made in the application of these emerging 2D materials, beyond graphene, for PSCs are presented. Both the advantages and challenges of these 2D materials for PSCs are highlighted. Finally, important directions for the future advancements toward efficient, low‐cost, and stable PSCs are outlined.

I/Br/Cl triple‐anion perovskite material with bandgap of 1.8 eV is tailored for indoor light harvesting, which realizes a record high indoor efficiency of 36.2% with increased open circuit voltage (V _oc) and minimal short‐circuit current ( J _sc) loss. The I/Br halide segregation is restrained by Cl‐involvement, realizing a long‐term stability of over 95% after 2000 h.

Abstract

Indoor photovoltaics are promising to enable self‐powered electronic devices for the Internet of Things. Here, reported is a triple‐anion CH₃NH₃PbI_{2− x} BrCl _x perovskite film, of which the bandgap is specially designed for indoor light harvesting to achieve a record high efficiency of 36.2% with distinctive high open circuit voltage (V _oc) of 1.028 V under standard 1000 lux fluorescent light. The involvement of both bromide and chloride suppresses the trap‐states and nonradiative recombination loss, exhibiting a remarkable ideality factor of 1.097. The introduction of chloride successfully restrains the halide segregation of iodide and bromide, stabilizing the triple‐anion perovskite film. The devices show an excellent long‐term performance, sustaining over 95% of original efficiency under continuous light soaking over 2000 h. These findings show the importance and potential of I/Br/Cl triple‐anion perovskite with tailored bandgap and suppressed trap‐states in stable and efficient indoor light recycling.

A high power conversion efficiency of 11.76%, the best efficiency for all‐polymer solar cells, is achieved by printing fabrication based on PTzBI‐Si:N2200 processing with 2‐methyltetrahydrofuran. A Multi‐length‐scaled morphology is found in the bulk heterojunctions, which ensures fast transfer of carriers and facilitates exciton separation, and boosts carrier mobility and current density, thus improving the device performance.

Abstract

All‐polymer solar cells (all‐PSCs) exhibit excellent stability and readily tunable ink viscosity, and are therefore especially suitable for printing preparation of large‐scale devices. At present, the efficiency of state‐of‐the‐art all‐PSCs fabricated by the spin‐coating method has exceeded 11%, laying the foundation for the preparation and practical utilization of printed devices. A high power conversion efficiency (PCE) of 11.76% is achieved based on PTzBI‐Si:N2200 all‐PSCs processing with 2‐methyltetrahydrofuran (MTHF, an environmentally friendly solvent) and preparation of active layers by slot die printing, which is the top efficient for all‐PSCs. Conversely, the PCE of devices processed by high‐boiling point chlorobenzene is less than 2%. Through the study of film formation kinetics, volatile solvents can freeze the morphology in a short time, and a more rigid conformation with strong intermolecular interaction combined with the solubility limit of PTzBI‐Si and N2200 in MTHF results in the formation of a fibril network in the bulk heterojunction. The multilength scaled morphology ensures fast transfer of carriers and facilitates exciton separation, which boosts carrier mobility and current density, thus improving the device performance. These results are of great significance for large‐scale printing fabrication of high‐efficiency all‐PSCs in the future.

A novel method is developed for fabricating high‐quality Ruddlesden–Popper perovskite films by directly using commercially available organic amines, avoiding extra chemical synthesis processing of organic ammonium halides. This new approach results in similar (and even better) device performance for both solar cells and light‐emitting diodes when compared with control devices fabricated from organic ammonium halides.

Abstract

Ruddlesden–Popper perovskites (RPPs), consisting of alternating organic spacer layers and inorganic layers, have emerged as a promising alternative to 3D perovskites for both photovoltaic and light‐emitting applications. The organic spacer layers provide a wide range of new possibilities to tune the properties and even provide new functionalities for RPPs. However, the preparation of state‐of‐the‐art RPPs requires organic ammonium halides as the starting materials, which need to be ex situ synthesized. A novel approach to prepare high‐quality RPP films through in situ formation of organic spacer cations from amines is presented. Compared with control devices fabricated from organic ammonium halides, this new approach results in similar (and even better) device performance for both solar cells and light‐emitting diodes. High‐quality RPP films are fabricated based on different types of amines, demonstrating the universality of the approach. This approach not only represents a new pathway to fabricate efficient devices based on RPPs, but also provides an effective method to screen new organic spacers with further improved performance.

Quantum dot solace: A hybrid ternary organic solar cell incorporating lead halide perovskite quantum dots boosts conversion efficiency. It exhibits improved exciton dissociation and suppressed recombination.

Abstract

The facile synthesis, solution‐processability, and outstanding optoelectronic properties of emerging colloidal lead halide perovskite quantum dots (LHP QDs) makes them ideal candidates for scalable and inexpensive optoelectronic applications, including photovoltaic (PV) devices. The first demonstration of integrating CsPbI₃ QDs into a conventional organic solar cell (OSC) involves embedding the LHP QDs in a donor–acceptor (PTB7‐Th:PC₇₁BM) bulk heterojunction. Optimizing the loading amount at 3 wt %, we demonstrate a power conversion efficiency of 10.8 %, which is a 35 % increase over control devices, and is a record amongst hybrid ternary OSCs. Detailed investigation into the mechanisms behind the performance enhancement shows that increased light absorption is not a factor, but that increased exciton separation in the acceptor phase and reduced recombination are responsible.

Herein, a facile method to improve the long‐term stability of perovskite solar cells using N719 dye molecules as additives is presented. Perovskite‐dye hybrid films show better crystallinity, enhanced light absorption, and boosted moisture stability. Due to the greatly retarded hydration process, the degradation process of perovskite‐dye solar cells is three times longer than that for pristine devices.

Metal‐halide perovskite solar cells (PSC) have shown great success in achieving high efficiencies but less satisfaction in achieving long‐term stability. Perovskites are prone to forming perovskite hydrates in humid environments, which leads to the decomposition of the perovskite materials. Herein, a common and cheap dye molecule, called cis‐di(thiocyanato)bis(2,2‐bipyridyl4,4‐dicarboxylate)ruthenium(II), denoted as N719, is introduced into mixed‐cation mixed‐halide perovskites for better moisture stability. It is discovered that the N719 molecules form perovskite‐dye complexes in the precursor solution, leading to larger grains and better film crystallinity by slowing down the crystallization process. Fourier‐transform infrared spectroscopy and X‐ray diffraction characterizations suggest that the N719 molecules exist in the crystallized perovskite films but are not incorporated into the perovskite crystal lattice. The presence of N719 molecules in perovskite films greatly retards the formation of perovskite hydrates due to a three‐times‐increased water migration barrier. Owing to these improvements, nonencapsulated N719‐PSC retain over 80% of their original efficiencies after aging under a high relative humidity of 60% for 250 h, which is three times longer than that for pristine cells. A cheap and effective route for controlling the perovskite crystallization process and improving the stability of PSC without sacrificing device efficiency is represented.

For enabling efficient scale‐up strategies in the field of perovskite photovoltaics, this work demonstrates general, quantitative modeling of the precursor thin‐film thickness evolution by controlling the drying process by a laminar air flow with simultaneous laser reflectometry. The model presented here enables the prediction of the perovskite thin‐film morphology for arbitrary dryers—yielding homogeneous perovskite absorber layers fabricated by blade coating.

Abstract

A key challenge for the commercialization of perovskite photovoltaics is the transfer of high‐quality spin coated perovskite thin‐films toward applying industry‐scale thin‐film deposition techniques, such as slot‐die coating, spray coating, screen printing, or inkjet printing. Due to the complexity of the formation of polycrystalline perovskite thin‐films from the precursor solution, efficient strategies for process transfer require advancing the understanding of the involved dynamic processes. This work investigates the fundamental interrelation between the drying dynamics of the precursor solution thin‐film and the quality of the blade coated polycrystalline perovskite thin‐films. Precisely defined drying conditions are established using a temperature‐stabilized drying channel purged with a laminar flow of dry air. The dedicated channel is equipped with laser reflectometry at multiple probing positions, allowing for in situ monitoring of the perovskite solution thin‐film thickness during the drying process. Based on the drying dynamics as measured at varying drying parameters, namely at varying temperature and laminar air flow velocity, a quantitative model on the drying of perovskite thin‐films is derived. This model enables process transfer to industry‐scale deposition systems beyond brute force optimization. Via this approach, homogeneous and pinhole‐free blade coated perovskite thin‐films are fabricated, demonstrating high power conversion efficiencies of up to 19.5% (17.3% stabilized) in perovskite solar cells.

I/Br/Cl triple‐anion perovskite material with bandgap of 1.8 eV is tailored for indoor light harvesting, which realizes a record high indoor efficiency of 36.2% with increased open circuit voltage (V _oc) and minimal short‐circuit current ( J _sc) loss. The I/Br halide segregation is restrained by Cl‐involvement, realizing a long‐term stability of over 95% after 2000 h.

Abstract

Indoor photovoltaics are promising to enable self‐powered electronic devices for the Internet of Things. Here, reported is a triple‐anion CH₃NH₃PbI_{2− x} BrCl _x perovskite film, of which the bandgap is specially designed for indoor light harvesting to achieve a record high efficiency of 36.2% with distinctive high open circuit voltage (V _oc) of 1.028 V under standard 1000 lux fluorescent light. The involvement of both bromide and chloride suppresses the trap‐states and nonradiative recombination loss, exhibiting a remarkable ideality factor of 1.097. The introduction of chloride successfully restrains the halide segregation of iodide and bromide, stabilizing the triple‐anion perovskite film. The devices show an excellent long‐term performance, sustaining over 95% of original efficiency under continuous light soaking over 2000 h. These findings show the importance and potential of I/Br/Cl triple‐anion perovskite with tailored bandgap and suppressed trap‐states in stable and efficient indoor light recycling.

Hysteresis in the dark, attributable to bias induced degradation of the p‐type interface, is investigated and eliminated in NiO‐based inverted perovskite solar cells. Enhanced stability to forward bias is obtained with the introduction of a low‐temperature hybrid magnesium‐based interlayer.

Abstract

In perovskite solar cells (PSCs), the interfaces are a weak link with respect to degradation. Electrochemical reactivity of the perovskite's halides has been reported for both molecular and polymeric hole selective layers (HSLs), and here it is shown that also NiO brings about this decomposition mechanism. Employing NiO as an HSL in p–i–n PSCs with power conversion efficiency (PCE) of 16.8%, noncapacitive hysteresis is found in the dark, which is attributable to the bias‐induced degradation of perovskite/NiO interface. The possibility of electrochemically decoupling NiO from the perovskite via the introduction of a buffer layer is explored. Employing a hybrid magnesium‐organic interlayer, the noncapacitive hysteresis is entirely suppressed and the device's electrical stability is improved. At the same time, the PCE is improved up to 18% thanks to reduced interfacial charge recombination, which enables more efficient hole collection resulting in higher V _oc and FF.

A new method is developed to synthesize SnO _x ‐Cl colloids and to realize an in situ and spontaneous ion‐exchange reaction during the perovskite film crystallization process. It is found that such ion exchange can perfectly passivate the interface defects and reduce energy loss at the interface.

Abstract

Interface engineering is of great concern in photovoltaic devices. For the solution‐processed perovskite solar cells, the modification of the bottom surface of the perovskite layer is a challenge due to solvent incompatibility. Herein, a Cl‐containing tin‐based electron transport layer; SnO _x ‐Cl, is designed to realize an in situ, spontaneous ion‐exchange reaction at the interface of SnO _x ‐Cl/MAPbI₃. The interfacial ion rearrangement not only effectively passivates the physical contact defects, but, at the same time, the diffusion of Cl ions in the perovskite film also causes longitudinal grain growth and further reduces the grain boundary density. As a result, an efficiency of 20.32% is achieved with an extremely high open‐circuit voltage of 1.19 V. This versatile design of the underlying carrier transport layer provides a new way to improve the performance of perovskite solar cells and other optoelectronic devices.

Grain boundaries (GBs) play an important role in most polycrystalline solar cells. In this essay, three important questions are explored: Do GBs affect: 1) recombination and thus open‐circuit voltage? Not dramatically, if at all; 2) current–voltage hysteresis? Most studies show that hysteresis is dominated by defects at GBs; and 3) long‐term durability? Yes, GBs definitely help increase the rate of perovskite degradation.

Abstract

Grain boundaries (GBs) play an important role in most polycrystalline solar cells. In perovskite solar cells, the research community is just starting to understand their effects on performance and long‐term durability. In this essay, three important questions are explored: Do GBs affect: 1) recombination and thus open‐circuit voltage? Not dramatically, if at all; 2) current–voltage hysteresis? Most studies show that hysteresis is dominated by defects at GBs; and 3) long‐term durability? Yes, GBs definitely help increase the rate of perovskite degradation. In this essay, the latest reports are summarized and the authors' perspective on this very important subject is given.

The spintronic properties of different hybrid organic–inorganic perovskites (HOIPs) are studied in spin valve devices, including spin diffusion length and spin lifetime, as well as the impact of the chemical components on these properties. This study aims at demonstrating promising spintronic applications of HOIPs, and providing a clear path for engineering spintronic devices based on HOIPs.

Abstract

The hybrid organic–inorganic perovskites (HOIPs) form a new class of semiconductors which show promising optoelectronic device applications. Remarkably, the optoelectronic properties of HOIP are tunable by changing the chemical components of their building blocks. Recently, the HOIP spintronic properties and their applications in spintronic devices have attracted substantial interest. Here the impact of the chemical component diversity in HOIPs on their spintronic properties is studied. Spin valve devices based on HOIPs with different organic cations and halogen atoms are fabricated. The spin diffusion length is obtained in the various HOIPs by measuring the giant magnetoresistance (GMR) response in spin valve devices with different perovskite interlayer thicknesses. In addition spin lifetime is also measured from the Hanle response. It is found that the spintronic properties of HOIPs are mainly determined by the halogen atoms, rather than the organic cations. The study provides a clear avenue for engineering spintronic devices based on HOIPs.

A high power conversion efficiency of 11.76%, the best efficiency for all‐polymer solar cells, is achieved by printing fabrication based on PTzBI‐Si:N2200 processing with 2‐methyltetrahydrofuran. A Multi‐length‐scaled morphology is found in the bulk heterojunctions, which ensures fast transfer of carriers and facilitates exciton separation, and boosts carrier mobility and current density, thus improving the device performance.

Abstract

All‐polymer solar cells (all‐PSCs) exhibit excellent stability and readily tunable ink viscosity, and are therefore especially suitable for printing preparation of large‐scale devices. At present, the efficiency of state‐of‐the‐art all‐PSCs fabricated by the spin‐coating method has exceeded 11%, laying the foundation for the preparation and practical utilization of printed devices. A high power conversion efficiency (PCE) of 11.76% is achieved based on PTzBI‐Si:N2200 all‐PSCs processing with 2‐methyltetrahydrofuran (MTHF, an environmentally friendly solvent) and preparation of active layers by slot die printing, which is the top efficient for all‐PSCs. Conversely, the PCE of devices processed by high‐boiling point chlorobenzene is less than 2%. Through the study of film formation kinetics, volatile solvents can freeze the morphology in a short time, and a more rigid conformation with strong intermolecular interaction combined with the solubility limit of PTzBI‐Si and N2200 in MTHF results in the formation of a fibril network in the bulk heterojunction. The multilength scaled morphology ensures fast transfer of carriers and facilitates exciton separation, which boosts carrier mobility and current density, thus improving the device performance. These results are of great significance for large‐scale printing fabrication of high‐efficiency all‐PSCs in the future.

A fullerene derivative, [6,6]‐phenyl‐C₆₁‐butyric acid‐N,N‐dimethyl‐3‐(2‐thienyl)propanam ester (PCBB‐S‐N), is designed and synthesized to correct defects in electron‐transporting layers (ETLs) and perovskite films. Its use leads to a promising power conversion efficiency (PCE) of 21.08% for perovskite solar cells. Importantly, devices containing PCBB‐S‐N simultaneously realize excellent thermal stability and water resistance.

Abstract

The poor long‐term stability of organic–inorganic hybrid halide perovskite solar cells (pero‐SCs) remains a big challenge for their commercialization. Although strategies such as encapsulation, doping, and passivation have been reported, there remains a lack of understanding of the water resistance and thermal stability of pero‐SCs. A fullerene derivative, [6,6]‐phenyl‐C₆₁‐butyric acid‐N,N‐dimethyl‐3‐(2‐thienyl)propanam ester (PCBB‐S‐N) containing a functional sulfur atom and C_60, is synthesized and employed as electron transporting layer (ETL)/intermediary layer to targetedly heal the multitype defects in pero‐SCs or assist the growth of ETL, such as [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM), in planar p‐i‐n pero‐SCs. The repaired pero‐SCs can not only dramatically improve their power conversion efficiencies, but also address stability issues under moisture and high temperature. The corresponding mechanism of PCBB‐S‐N with targeted therapy effect in a device is systematically investigated by both experiments and theoretical calculation. This work demonstrates that the proposed fullerene derivative with finely tuned chemical structure can be a promising ETL candidate or intermediary to approach stable and efficient planar p‐i‐n pero‐SCs.

The fused‐ring acceptor IT‐M is added into an unfused‐core acceptor‐based binary blend of PBDB‐TF:HC‐PCIC. Notable fill factor enhancement and a broad compositional tolerance are achieved for the ternary solar cells. Thus, the power conversion efficiency is significantly improved from 11.14% for binary devices to 12.34% for ternary cells.

The ternary blend strategy has shown great potential to improve the photovoltaic performance of organic solar cells (OSCs). Usually, adopting two acceptors with similar chemical structures shows good compatibility but limited enhancement in performance, whereas adopting two acceptors with different chemical structures always has a compositional sensitivity issue. Herein, a highly efficient ternary OSC with an enhanced fill factor (FF) and a broad compositional tolerance is demonstrated by introducing the fused‐ring acceptor IT‐M to a binary blend based on an unfused‐core acceptor HC‐PCIC and polymer donor PBDB‐TF. Detailed studies on the optical, electrical, and morphological properties of ternary blends reveal the process of charge dynamics and work mechanisms in the ternary device. It is found that the addition of IT‐M into the PBDB‐TF:HC‐PCIC binary blend not only adapts to the parallel‐like model, but also optimizes the morphology and domain sizes in the ternary blend, resulting in a reduced trap‐assisted recombination and suppressed bimolecular recombination. Consequently, open‐circuit voltage (V _oc), short‐circuit current density (J _sc), and FF are synergistically enhanced, leading to an improved power conversion efficiency (PCE) of 12.34% with a high V _oc of 0.88 V, an increased J _sc of 18.69 mA cm⁻², and an enhanced FF of 73.82% for the ternary device with 5% IT‐M content. Moreover, the PCEs of ternary OSCs remain above 11% within an IT‐M ratio of 2.5–50%, exhibiting a broad compositional tolerance, which is rarely reported in fullerene‐free ternary OSCs.

Balancing act: The indeno[1,2‐b]carbazole donor not only combines the characteristics of carbazole and fluorene, but also exhibits excellent thermal stability and high hole mobility as a result of the bulky planar structure. Hole‐transporting materials based on this methoxy‐free donor demonstrate a high efficiency and stability simultaneously, providing a promising strategy for developing efficient and stable perovskite‐based solar cells.

Abstract

With perovskite‐based solar cells (PSCs) now reaching efficiencies of greater than 20 %, the stability of PSC devices has become a critical challenge for commercialization. However, most efficient hole‐transporting materials (HTMs) thus far still rely on the state‐of‐the‐art methoxy triphenylamine (MOTPA) donor unit in which methoxy groups usually reduce the device stability. Herein, a carbazole‐fluorene hybrid has been employed as a methoxy‐free donor to construct organic HTMs. The indeno[1,2‐b]carbazole group not only inherits the characteristics of carbazole and fluorene, but also exhibits additional advantages arising from the bulky planar structure. Consequently, M129, endowed with indeno[1,2‐b]carbazole simultaneously exhibits a promising efficiency of over 20 % and superior long‐term stability. The hybrid strategy toward the methoxy‐free donor opens a new avenue for developing efficient and stable HTMs.