awn

Acetic acid (Ac) is used as an antisolvent for preparing perovskite films with excellent optoelectronic properties. Ac is found to not only reduce perovskite film roughness and residual PbI₂ but also generate a passivation effect from the electron‐rich carbonyl group. The best 0.159 cm² devices produce efficiencies of 22.0% for Cs_0.05FA_0.80MA_0.15Pb(I_0.85Br_0.15)₃ and 23.0% for Cs_0.05FA_0.90MA_0.05Pb(I_0.95Br_0.05)₃.

Abstract

Improving the quality of perovskite poly‐crystalline film is essential for the performance of associated solar cells approaching their theoretical limit efficiency. Pinholes, unwanted defects, and nonperovskite phase can be easily generated during film formation, hampering device performance and stability. Here, a simple method is introduced to prepare perovskite film with excellent optoelectronic property by using acetic acid (Ac) as an antisolvent to control perovskite crystallization. Results from a variety of characterizations suggest that the small amount of Ac not only reduces the perovskite film roughness and residual PbI₂ but also generates a passivation effect from the electron‐rich carbonyl group (CO) in Ac. The best devices produce a PCE of 22.0% for Cs_0.05FA_0.80MA_0.15Pb(I_0.85Br_0.15)₃ and 23.0% for Cs_0.05FA_0.90MA_0.05Pb(I_0.95Br_0.05)₃ on 0.159 cm² with negligible hysteresis. This further improves device stability producing a cell that maintained 96% of its initial efficiency after 2400 h storage in ambient environment (with controlled relative humidity (RH) <30%) without any encapsulation.

Nanoporous Au film is successfully introduced into perovskite solar cells to replace the typical thermal deposition of metal electrode with a high efficiency of 19.0% on rigid substrate and sustains an excellent bending durability of 98.5% even after 1000 cycles testing on a flexible device, while its facile and recycled utilization significantly reduces the device fabrication cost, noble metal consuming, and environmental pollution.

Abstract

Perovskite solar cells (PSCs) using metal electrodes have been regarded as promising candidates for next‐generation photovoltaic devices because of their high efficiency, low fabrication temperature, and low cost potential. However, the complicated and rigorous thermal deposition process of metal contact electrodes remains a challenging issue for reducing the energy pay‐back period in commercial PSCs, as the ubiquitous one‐time use of a contact electrode wastes limited resources and pollutes the environment. Here, a nanoporous Au film electrode fabricated by a simple dry transfer process is introduced to replace the thermally evaporated Au electrode in PSCs. A high power conversion efficiency (PCE) of 19.0% is demonstrated in PSCs with the nanoporous Au film electrode. Moreover, the electrode is recycled more than 12 times to realize a further reduced fabrication cost of PSCs and noble metal materials consumption and to prevent environmental pollution. When the nanoporous Au electrode is applied to flexible PSCs, a PCE of 17.3% and superior bending durability of ≈98.5% after 1000 cycles of harsh bending tests are achieved. The nanoscale pores and the capability of the porous structure to impede crack generation and propagation enable the nanoporous Au electrode to be recycled and result in excellent bending durability.

Efficient vacuum‐assisted growth control (VAGC) allows growing micron‐sized and pinhole‐free low bandgap (E _G ≈ 1.27 eV) perovskite thin‐films for fabrication of efficient low‐bandgap perovskite solar cells. This efficient low‐bandgap perovskite solar cells enable achieving efficient all‐perovskite tandem solar cells. VAGC exhibits promising reproducibility and potential in larger active‐area solar cells up to 1 cm². More details can be found in article number https://doi.org/10.1002/aenm.2019025831902583 by Bahram Abdollahi Nejand, Ulrich W. Paetzold, and co‐workers.

Acetic acid (Ac) is used as an antisolvent for preparing perovskite films with excellent optoelectronic properties. Ac is found to not only reduce perovskite film roughness and residual PbI₂ but also generate a passivation effect from the electron‐rich carbonyl group. The best 0.159 cm² devices produce efficiencies of 22.0% for Cs_0.05FA_0.80MA_0.15Pb(I_0.85Br_0.15)₃ and 23.0% for Cs_0.05FA_0.90MA_0.05Pb(I_0.95Br_0.05)₃.

Abstract

Improving the quality of perovskite poly‐crystalline film is essential for the performance of associated solar cells approaching their theoretical limit efficiency. Pinholes, unwanted defects, and nonperovskite phase can be easily generated during film formation, hampering device performance and stability. Here, a simple method is introduced to prepare perovskite film with excellent optoelectronic property by using acetic acid (Ac) as an antisolvent to control perovskite crystallization. Results from a variety of characterizations suggest that the small amount of Ac not only reduces the perovskite film roughness and residual PbI₂ but also generates a passivation effect from the electron‐rich carbonyl group (CO) in Ac. The best devices produce a PCE of 22.0% for Cs_0.05FA_0.80MA_0.15Pb(I_0.85Br_0.15)₃ and 23.0% for Cs_0.05FA_0.90MA_0.05Pb(I_0.95Br_0.05)₃ on 0.159 cm² with negligible hysteresis. This further improves device stability producing a cell that maintained 96% of its initial efficiency after 2400 h storage in ambient environment (with controlled relative humidity (RH) <30%) without any encapsulation.

A multistimuli‐responsive composite with locally controlled texture that can be printed into programmable shape‐morphing architectures is presented. The printed structures show fast, reversible, and multistimuli‐responsive shape‐morphing toward heat, light, and water (liquid and vapor).

Abstract

Natural materials are often compositionally and structurally heterogeneous for realizing particular functions. Inspired by nature, researchers have designed hybrid materials that possess properties beyond each of the components. Particularly, it remains a great challenge to realize site‐specific anisotropy, which widely exists in natural materials and is responsible for unique mechanical properties as well as physiological behaviors. Herein, the spontaneous formation of aligned graphene oxide (GO) flakes in sodium alginate (SA) matrix with locally controlled orientation via a direct‐ink‐writing printing process is reported. The GO flakes are spontaneously aligned in the SA matrix by shear force when being extruded and then arranged horizontally after drying on the substrate, forming a brick‐and‐mortar structure that could anisotropically contract or expand upon activation by heat, light, or water. By designing the printing pathways directed by finite element analysis, the orientation of GO flakes in the composite is locally controlled, which could further guide the composite to transform into versatile architectures. Particularly, the transformation is reversible when water vapor is applied as one of the stimuli. As a proof of concept, complex morphing architectures are experimentally demonstrated, which are in good consistency with the simulation results.

The use of two precursor preparation methods for the deposition of phenethylammonium‐containing organic‐inorganic hybrid perovskite films for photovoltaic applications is reported. It is found that film properties, photovoltaic device performance, and stability differ depending on the precursor preparation methods. These new insights are important for optimizing precursor preparations for lower dimensional perovskite films to achieve the best device performance and stability.

For the fabrication of low‐dimensional perovskite solar cells, understanding the effect of precursor preparation on film formation is critical to achieve high‐quality perovskite film and, therefore, high efficiency in related solar devices. Herein, the two methods to prepare phenethylammonium‐based mixed perovskite precursors with the same chemical composition are reported. These methods are called 1) different phase (DP) and 2) same phase (SP) methods as the former involves the mixing of a 3D perovskite precursor with a 2D perovskite precursor, whereas the latter involves the mixing of quasi‐2D perovskite precursors. The films prepared by these methods are characterized by X‐ray diffraction, Kelvin probe force microscopy, and scanning electron microscopy, revealing different perovskite structures. The power conversion efficiency (PCE) of the champion cells by DP and SP methods reaches 19.1% and 18.9%, respectively. Results of the aging test show a dramatic improvement in the stability of SP perovskite devices maintaining 86% of its initial performance after exposure to a relative humidity (RH) 8 ± 5% for 1000 hr and over 80% of its initial PCE after continuous 1 sun illumination (including UV) at RH 70%. The new insights provided by this work are important to design perovskite precursor preparation methods for the best device performance and stability.

A comparative investigation of single‐donor component and different donor:acceptor blend ratio‐based organic solar cells (OSCs) is conducted using BTID‐0F as the donor and PC₇₁BM as the acceptor. The highest PCEs of 1.61% for single‐donor and 8.47% for BTID‐0F:PC₇₁BM‐based OSCs are obtained. Herein, the mechanism of charge generation in organic materials, thus obtaining high‐efficient single‐component OSCs, is analyzed.

Organic solar cells (OSCs) require a bulk heterojunction of a donor and an acceptor for efficient charge generation, whereas other types of solar cells normally use the p‐i‐n device structure. Herein, a comparative investigation of the p‐i‐n‐structured OSCs is conducted based on single‐donor‐component BTID‐0F and the bulkheterojuction OSCs with different donor:acceptor blend ratios using BTID‐0F as the donor and PC₇₁BM as the acceptor. The highest power conversion efficiency (PCE) of 1.61% is obtained for single‐donor‐based OSCs. The impact of PC₇₁BM weight ratio in BTID‐0F:PC₇₁BM‐based OSCs upon blend morphology, material energetics, photogenerated charge dynamic process, and photovoltaic device performance is investigated, and the highest PCE reaches 8.47%. Results indicate that even when the acceptor sites are highly diluted and the acceptor phase is discontinuous, electron transport can occur with a reasonable electron mobility. The PCE of 1.61% is the highest PCE reported for p‐i‐n structure OSCs based on a single‐donor component, which is helpful to understand the mechanism of charge generation in organic materials and thus obtainhigh‐efficient OSCs using the p‐i‐n structure.

A novel emulsion‐based bottom‐up self‐assembly strategy is used to prepare sizable SnO₂ microspheres from oleic acid capped SnO₂ nanorods. Combined with an in‐situ ligand‐stripping strategy, the low‐temperature solution‐processed mesoscopic perovskite solar cells (PSCs) can achieve an efficiency as high as 21.35% with slight hysteresis and good reproducibility. This novel route will greatly expand the material selection range for preparing efficient mesoscopic PSCs.

Mesoporous scaffolds in perovskite solar cells (PSCs) can accelerate the formation of heterogeneous nucleation sites, leading to enhanced quality of perovskite films and uniform perovskite coverage over large areas. Nevertheless, the mesoporous electron transport layers (ETLs) can effectively compensate for the drawback of shorter electron diffusion lengths than their hole counterparts. Therefore, most mesoscopic PSCs usually show superior photovoltaic performance to their planar counterparts. However, mesoporous ETLs, particularly those prepared with metal oxide nanocrystals, often require a high‐temperature sintering process for the removal of residual organics and the improved crystallization of metal oxides. Here, a novel emulsion‐based bottom‐up self‐assembly strategy is used to prepare sizable SnO₂ microspheres from oleic acid capped SnO₂ nanorods. Combined with an in‐situ ligand‐stripping strategy, the low‐temperature solution‐processed mesoscopic PSCs can achieve efficiency as high as 21.35% with slight hysteresis and good reproducibility. In particular, the emulsion‐based bottom‐up self‐assembly strategy is a general way for preparing microspheres from several kinds of semiconductor nanocrystals, so it will greatly expand the material selection range for preparing efficient mesoscopic PSCs and even inverted mesoscopic devices.

Hole transport material (HTM) plays important roles in n–i–p type perovskite solar cells. It affects both efficiency and the stability. After the recognition of its importance, a number of HTMs have been developed. This review summarizes various types of HTMs and discusses their development.

Abstract

With the application of organic–inorganic hybrid perovskites to liquid‐type solar cells, the unprecedented development of perovskite solar cells (Per‐SCs) has been boosted by the introduction of solid‐state hole transport materials (HTMs). The removal of liquid electrolyte has lead to improved efficiency and stability. Supported by high‐quality perovskite films, the certified efficiency of Per‐SCs has reached 25.2%. For Per‐SCs assembled in a conventional structure (n–i–p), the hole transport layer (HTL) plays an extra role in preventing the perovskite layer from external stimuli. In summary, the successful design and fabrication of the HTL must meet various requirements in terms of solubility, hole transport, recombination prevention, stability, and reproducibility, to name but a few. Many research strategies are focused on the development of high‐performance HTMs to meet such requirements. Such strategies for the development of HTMs employed in conventional n–i–p solar cells are reviewed herein. A vision of the future HTMs is proposed in this review based on the already proposed solutions and current trends.

Molecules with controlled electron affinity processed at low temperature are used to tailor conductivity and the energy levels of hole transporting materials (HTMs), enabling fast holes extraction at the HTM/perovskite interface. This method with novel 3,6‐difluoro‐2,5,7,7,8,8‐hexacyanoquinodimethane enables the highest reported power conversion efficiency (PCE) of 22.13% and 20.01% for NiO _x ‐based rigid and flexible perovskite solar cells, respectively.

Abstract

Inverted perovskite solar cells (PSCs) with low‐temperature processed hole transporting materials (HTMs) suffer from poor performance due to the inferior hole‐extraction capability at the HTM/perovskite interfaces. Here, molecules with controlled electron affinity enable a HTM with conductivity improved by more than ten times and a decreased energy gap between the Fermi level and the valence band from 0.60 to 0.24 eV, leading to the enhancement of hole‐extraction capacity by five times. As a result, the 3,6‐difluoro‐2,5,7,7,8,8‐hexacyanoquinodimethane molecules are used for the first time enhancing open‐circuit voltage (V _oc) and fill factor (FF) of the PSCs, which enable rigid‐and flexible‐based inverted perovskite devices achieving highest power conversion efficiencies of 22.13% and 20.01%, respectively. This new method significantly enhances the V _oc and FF of the PSCs, which can be widely combined with HTMs based on not only NiO _x but also PTAA, PEDOTT:PSS, and CuSCN, providing a new way of realizing efficient inverted PSCs.

It is found that unique adducts form between CsI and dimethyl sulfoxide (DMSO) and certain antisolvents, such as methyl acetate, during film formation of the all‐inorganic perovskite CsPbI₃. These adducts significantly influence crystallization and the power conversion efficiency of the resulting solar cells.

Abstract

The excellent optoelectronic properties demonstrated by hybrid organic/inorganic metal halide perovskites are all predicated on precisely controlling the exact nucleation and crystallization dynamics that occur during film formation. In general, high‐performance thin films are obtained by a method commonly called solvent engineering (or antisolvent quench) processing. The solvent engineering method removes excess solvent, but importantly leaves behind solvent that forms chemical adducts with the lead‐halide precursor salts. These adduct‐based precursor phases control nucleation and the growth of the polycrystalline domains. There has not yet been a comprehensive study comparing the various antisolvents used in different perovskite compositions containing cesium. In addition, there have been no reports of solvent engineering for high efficiency in all‐inorganic perovskites such as CsPbI₃. In this work, inorganic perovskite composition CsPbI₃ is specifically targeted and unique adducts formed between CsI and precursor solvents and antisolvents are found that have not been observed for other A‐site cation salts. These CsI adducts control nucleation more so than the PbI₂–dimethyl sulfoxide (DMSO) adduct and demonstrate how the A‐site plays a significant role in crystallization. The use of methyl acetate (MeOAc) in this solvent engineering approach dictates crystallization through the formation of a CsI–MeOAc adduct and results in solar cells with a power conversion efficiency of 14.4%.

A soft template‐controlled growth (STCG) method is proposed for the fabrication of a pinhole‐free CsPbI₃ film and the device exhibits an efficiency of 16.04%. By suppressing the inductive effect of defects on the phase transition and utilizing the unique reversibility of the phase transition, the STCG‐based all‐inorganic solar cell retains 90% of its initial efficiency after 3000 h of light soaking and heating.

Abstract

The unfavorable morphology and inefficient utilization of phase transition reversibility have limited the high‐temperature‐processed inorganic perovskite films in both efficiency and stability. Here, a simple soft template‐controlled growth (STCG) method is reported by introducing (adamantan‐1‐yl)methanammonium to control the nucleation and growth rate of CsPbI₃ crystals, which gives rise to pinhole‐free CsPbI₃ film with a grain size on a micrometer scale. The STCG‐based CsPbI₃ perovskite solar cell exhibits a power conversion efficiency of 16.04% with significantly reduced defect densities and charge recombination. More importantly, an all‐inorganic solar cell with the architecture fluorine‐doped tin oxide (FTO)/NiO _x /STCG‐CsPbI₃/ZnO/indium‐doped tin oxide (ITO) is successfully fabricated to demonstrate its real advantage in thermal stability. By suppressing the inductive effect of defects during the phase transition and utilizing the unique reversibility of the phase transition for the high‐temperature‐processed CsPbI₃ film, the all‐inorganic solar cell retains 90% of its initial efficiency after 3000 h of continuous light soaking and heating.

By introduction of a multiple ligand (pentaerythritol tetrakis(3‐mercaptopropionate)), uncoordinated Pb²⁺ and Pb⁰ defects are simultaneously passivated. Meanwhile, better energy level matching between the valence band of perovskite and the highest occupied molecular orbital of the HTM is achieved. As a result, perovskite solar cell efficiency increases from 19.0% to 21.4% after surface passivation by multiple ligands.

Abstract

In the past decade, the efficiency of perovskite solar cells quickly increased from 3.8% to 25.2%. The quality of perovskite films plays vital role in device performance. The films fabricated by solution‐process are usually polycrystalline, with significantly higher defect density than that of single crystal. One kind of defect in the films is uncoordinated Pb²⁺, which is usually generated during thermal annealing process due to the volatile organic component. Another detrimental kind of defect is Pb⁰, which is often observed during the film fabrication process or solar cell operation. Because the open circuit voltage has a close relation with the defect density, it is thus desirable to passivate these two kinds of defects. Here, a molecule with multiple ligands is introduced, which not only passivates the uncoordinated Pb²⁺ defects, but also suppresses the formation of Pb⁰ defects. Meanwhile, such a treatment improves the energy level alignment between the valence band of perovskite and the highest occupied molecular orbital of spiro‐OMeTAD. As a result, the performance of perovskite solar cells significantly increases from 19.0% to 21.4%.

Solvation of PbI₂ promotes the intercalation of solvent molecules with formamidinium iodide to form the perovskite phase of FAPbI₃ directly at room temperature. Subsequent annealing completes the conversion and yields high‐quality perovskite films with reduced trap state density and a high power conversion efficiency.

Abstract

The two‐step conversion process consisting of metal halide deposition followed by conversion to hybrid perovskite has been successfully applied toward producing high‐quality solar cells of the archetypal MAPbI₃ hybrid perovskite, but the conversion of other halide perovskites, such as the lower bandgap FAPbI₃, is more challenging and tends to be hampered by the formation of hexagonal nonperovskite polymorph of FAPbI₃, requiring Cs addition and/or extensive thermal annealing. Here, an efficient room‐temperature conversion route of PbI₂ into the α‐FAPbI₃ perovskite phase without the use of cesium is demonstrated. Using in situ grazing incidence wide‐angle X‐ray scattering (GIWAXS) and quartz crystal microbalance with dissipation (QCM‐D), the conversion behaviors of the PbI₂ precursor from its different states are compared. α‐FAPbI₃ forms spontaneously and efficiently at room temperature from P₂ (ordered solvated polymorphs with DMF) without hexagonal phase formation and leads to complete conversion after thermal annealing. The average power conversion efficiency (PCE) of the fabricated solar cells is greatly improved from 16.0(±0.32)% (conversion from annealed PbI₂) to 17.23(±0.28)% (from solvated PbI₂) with a champion device PCE > 18% due to reduction of carrier recombination rate. This work provides new design rules toward the room‐temperature phase transformation and processing of hybrid perovskite films based on FA⁺ cation without the need for Cs⁺ or mixed halide formulation.

Semi‐transparent perovskite solar cells (ST‐PSCs) have received great attention due to their promising applications in many areas, such as building integrated photovoltaics (BIPV), tandem devices, and wearable electronics. A general overview of recent advances in ST‐PSCs from materials and devices to applications is provided, and presented alongside some personal perspectives on their future development.

Abstract

Semitransparent solar cells (ST‐SCs) have received great attention due to their promising application in many areas, such as building integrated photovoltaics (BIPVs), tandem devices, and wearable electronics. In the past decade, perovskite solar cells (PSCs) have revolutionized the field of photovoltaics (PVs) with their high efficiencies and facile preparation processes. Due to their large absorption coefficient and bandgap tunability, perovskites offer new opportunities to ST‐SCs. Here, a general overview is provided on the recent advances in ST‐PSCs from materials and devices to applications and some personal perspectives on the future development of ST‐PSCs.

Interfaces provide reactive zones and interphases stabilize electronic device operation. Understanding and designing interfaces and interphases represent an effective and efficient way for developing high‐performance rechargeable batteries and perovskite solar cells.

Abstract

The ever‐increasing demand for clean sustainable energy has driven tremendous worldwide investment in the design and exploration of new active materials for energy conversion and energy‐storage devices. Tailoring the surfaces of and interfaces between different materials is one of the surest and best studied paths to enable high‐energy‐density batteries and high‐efficiency solar cells. Metal‐halide perovskite solar cells (PSCs) are one of the most promising photovoltaic materials due to their unprecedented development, with their record power conversion efficiency (PCE) rocketing beyond 25% in less than 10 years. Such progress is achieved largely through the control of crystallinity and surface/interface defects. Rechargeable batteries (RBs) reversibly convert electrical and chemical potential energy through redox reactions at the interfaces between the electrodes and electrolyte. The (electro)chemical and optoelectronic compatibility between active components are essential design considerations to optimize power conversion and energy storage performance. A focused discussion and critical analysis on the formation and functions of the interfaces and interphases of the active materials in these devices is provided, and prospective strategies used to overcome current challenges are described. These strategies revolve around manipulating the chemical compositions, defects, stability, and passivation of the various interfaces of RBs and PSCs.

A highly phase‐stable perovskite film without the methylammonium cation is fabricated by introducing cesium chloride in the double cation Cs, formamidinium perovskite precursor, leading to high power conversion efficiency of 20.5% and remarkable long‐term stability. The unencapsulated perovskite solar cell retains about 80% of its initial efficiency after a 1000 h aging study, demonstrating a feasible approach to enhance solar cell efficiency and stability simultaneously.

Abstract

Organic–inorganic metal halide perovskite solar cells (PSCs) have achieved certified power conversion efficiency (PCE) of 25.2% with complex compositional and bandgap engineering. However, the thermal instability of methylammonium (MA) cation can cause the degradation of the perovskite film, remaining a risk for the long‐term stability of the devices. Herein, a unique method is demonstrated to fabricate highly phase‐stable perovskite film without MA by introducing cesium chloride (CsCl) in the double cation (Cs, formamidinium) perovskite precursor. Moreover, due to the suboptimal bandgap of bromide (Br⁻), the amount of Br⁻ is regulated, leading to high power conversion efficiency. As a result, MA‐free perovskite solar cells achieve remarkable long‐term stability and a PCE of 20.50%, which is one of the best results for MA‐free PSCs. Moreover, the unencapsulated device retains about 80% of the original efficiencies after a 1000 h aging study. These results provide a feasible approach to enhance solar cell stability and performance simultaneously, paving the way for commercializing PSCs.

A‐site management by introducing an A‐site placeholder cation, NH₄ ⁺, during the perovskite crystallization process is proposed to balance the supersaturation discrepancy between AX and BX₂ so as to improve its crystal quality without any residue. Most importantly, the sharply decreased A‐site‐related defect I_MA indicates that it is responsible for such crystalline optimization.

Abstract

An in‐depth understanding and effective suppression of nonradiative recombination pathways in perovskites are crucial to their crystallization process, in which supersaturation discrepancies at different time scales between CH₃NH₃I (MAI, methylammonium iodide) and PbI₂ remain a key issue. Here, an A‐site management strategy via the introduction of an A‐site placeholder cation, NH₄ ⁺, to offset the deficient MA⁺ precipitation by occupying the cavity of Pb–I framework, is proposed. The temporarily remaining NH₄ ⁺ is substituted by subsequently precipitated MA⁺. The temperature‐dependent crystallization process with the generation and consumption of a transient phase is sufficiently demonstrated by the dynamic changes in crystal structure characteristic peaks through in situ grazing‐incidence X‐ray diffraction and the surface potential difference evolution through temperature‐dependent Kelvin probe force microscopy. A highly crystalline perovskite is consequently acquired, indicated by the enlarged grain size, lowered nonradiative defect density, prolonged carrier lifetime, and fluorescence lifetime imaging. Most importantly, it is identified that the A‐site I_MA defect is responsible for such crystal quality optimization based on theoretical calculations, transient absorption, and deep‐level transient spectroscopy. Furthermore, the universality of the proposed A‐site management strategy is demonstrated with other mixed‐cation perovskite systems, indicating that this methodology successfully provides guidance for synthesis route design of highly crystalline perovskites.

Through a strategy of embedding cyclohexane‐1,4‐dione into the thieno[3,4‐b]thiophene unit, a highly electron‐deficient core (TTDO) is synthesized, and the corresponding donor polymer (PBTT‐F) is also developed. The nonfullerene photovoltaic device based on this new donor polymer exhibits an outstanding PCE of 16.1% with a very high fill factor of 77.1%, which demonstrates it a very promising donor for high‐performance solar cells.

Abstract

It is of great significance to develop efficient donor polymers during the rapid development of acceptor materials for nonfullerene bulk‐heterojunction (BHJ) polymer solar cells. Herein, a new donor polymer, named PBTT‐F, based on a strongly electron‐deficient core (5,7‐dibromo‐2,3‐bis(2‐ethylhexyl)benzo[1,2‐b:4,5‐c′]dithiophene‐4,8‐dione, TTDO), is developed through the design of cyclohexane‐1,4‐dione embedded into a thieno[3,4‐b]thiophene (TT) unit. When blended with the acceptor Y6, the PBTT‐F‐based photovoltaic device exhibits an outstanding power conversion efficiency (PCE) of 16.1% with a very high fill factor (FF) of 77.1%. This polymer also shows high efficiency for a thick‐film device, with a PCE of ≈14.2% being realized for an active layer thickness of 190 nm. In addition, the PBTT‐F‐based polymer solar cells also show good stability after storage for ≈700 h in a glove box, with a high PCE of ≈14.8%, which obviously shows that this kind of polymer is very promising for future commercial applications. This work provides a unique strategy for the molecular synthesis of donor polymers, and these results demonstrate that PBTT‐F is a very promising donor polymer for use in polymer solar cells, providing an alternative choice for a variety of fullerene‐free acceptor materials for the research community.