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Nature Communications, Published online: 22 April 2020; doi:10.1038/s41467-020-15790-z

The hygroscopic characteristics of dopants in 2,2′,7,7′‐tetrakis(N ,N ‐di‐p ‐methoxyphenylamine)‐9,9′‐spirobifluorene (spiro‐MeOTAD) hole‐transporting layers (HTLs) result in the degradation of both HTL morphology and device performance. A detailed study on the effects of initial morphology is presented. Accumulated lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is the key factor causing poor stability. Performing thermal annealing on HTL can improve the air stability greatly.

Abstract

Doped 2,2′,7,7′‐tetrakis(N ,N ‐di‐p ‐methoxyphenylamine)‐9,9′‐spirobifluorene (spiro‐MeOTAD), which acts as a hole‐transporting layer (HTL), endows perovskite solar cells (PSCs) with excellent performance. However, the intrinsically hygroscopic nature of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) dopants also aggravates the moisture instability of PSCs. In this work, the origins of the moisture instability of spiro‐MeOTAD HTLs are explored and strategies to enhance moisture resistance are proposed. After 780 h of aging in air, 52% of the initial power conversion efficiency (PCE) can be sustained by prolonging the mixing time of the precursor solution of spiro‐MeOTAD to reduce accumulated LiTFSI. In contrast, only 7% of the initial PCE remains if the precursor solution is mixed briefly. By thermally annealing an HTL to evaporate residual tBP in spiro‐MeOTAD, pinholes are completely eliminated and 65% of the initial PCE remains after the same aging time. In this study, the significance of the initial morphology of spiro‐MeOTAD HTLs on device stability is analyzed and strategies based on physical morphology for controlling PSC moisture instability induced by HTL dopants are developed.

Herein, studies about the degradation mechanism and stability improving strategies of organic solar cells (OSCs) in the past few years are reviewed. The current inconsistency in the stability measurement and the importance of the International Summit on Organic Photovoltaic Stability standards are discussed, and outlooks and research directions in the stability of OSCs in the near future are proposed.

Abstract

The organic solar cell (OSC) is a promising emerging low‐cost thin film photovoltaics technology. The power conversion efficiency (PCE) of OSCs has overpassed 16% for single junction and 17% for organic–organic tandem solar cells with the development of low bandgap organic materials synthesis and device processing technology. The main barrier of commercial use of OSCs is the poor stability of devices. Herein, the factors limiting the stability of OSCs are summarized. The limiting stability factors are oxygen, water, irradiation, heating, metastable morphology, diffusion of electrodes and buffer layers materials, and mechanical stress. The recent progress in strategies to increase the stability of OSCs is surveyed, such as material design, device engineering of active layers, employing inverted geometry, optimizing buffer layers, using stable electrodes and encapsulation materials. The International Summit on Organic Photovoltaic Stability guidelines are also discussed. The potential research strategies to achieve the required device stability and efficiency are highlighted, rendering possible pathways to facilitate the viable commercialization of OSCs.

Lead‐free Cs₂AgBiCl₆ double perovskite films with balanced stoichiometry, compact morphology, and high crystallinity are fabricated by a sequential vapor deposition method. Their application is explored as an ultraviolet photodetector which realizes low dark current density (≈10⁻⁷ mA cm⁻²), high detectivity (≈10¹² Jones), and stability (4 months). This work reveals the potential of Cs₂AgBiCl₆ double perovskites in ultraviolet detection.

Abstract

Double perovskites have shown great potentials in addressing the toxicity and instability issues of lead halide perovskites toward practical applications. However, fabrication of high‐quality double perovskite thin films has remained challenging. Here, sequential vapor deposition is used to fabricate high‐quality Cs₂AgBiCl₆ perovskite films with balanced stoichiometry, superior morphology, and highly oriented crystallinity, with an indirect bandgap of 2.41 eV. Using a diode structure, self‐powered Cs₂AgBiCl₆ ultraviolet (UV) photodetectors are demonstrated with high selectivity centered at 370 nm, with low dark current density (≈10⁻⁷ mA cm⁻²), high photoresponsivity (≈10 mA W⁻¹), and detectivity (≈10¹² Jones). Its detectivity is among the highest in all double‐perovskite‐based photodetectors reported to date and surpassing the performance of other perovskite photodetectors as well as metal oxide in the UV range. The devices also show excellent environmental and irradiation stability comparable to state‐of‐the‐art UV detectors. The findings help pave the way toward application of double perovskites in optoelectronic devices.

In situ growth of high‐quality CsPbBr₃ perovskite single crystal arrays directly on an electron transport layer of cubic zinc oxide (c‐ZnO) via a facile spin‐coating method is presented. CsPbBr₃ and c‐ZnO can match moderately attributed to the epitaxial lattice coherence. The interface toward c‐ZnO heterogeneous layer is a major step toward the realization of better integration of perovskites and inorganic transport layers.

Abstract

Directly growing perovskite single crystals on charge carrier transport layers will unravel a promising route for the development of emerging optoelectronic devices. Herein, in situ growth of high‐quality all‐inorganic perovskite (CsPbBr₃) single crystal arrays (PeSCAs) on cubic zinc oxide (c‐ZnO) is reported, which is used as an inorganic electron transport layer in optoelectronic devices, via a facile spin‐coating method. The PeSCAs consist of rectangular thin microplatelets of 6–10 µm in length and 2–3 µm in width. The deposited c‐ZnO enables the formation of phase‐pure and highly crystallized cubic perovskites via an epitaxial lattice coherence of (100)_CsPbBr3∥(100)_c‐ZnO, which is further confirmed by grazing incidence wide‐angle X‐ray scattering. The PeSCAs demonstrate a significant structural stability of 26 days with a 9 days excellent photoluminescence stability in ambient environment, which is much superior to the perovskite nanocrystals (PeNCs). The high crystallinity of the PeSCAs allows for a lower density of trap states, longer carrier lifetimes, and narrower energetic disorder for excitons, which leads to a faster diffusion rate than PeNCs. These results unravel the possibility of creating the interface toward c‐ZnO heterogeneous layer, which is a major step for the realization of a better integration of perovskites and charge carrier transport layers.

A multifunctional N719 dye interlayer is introduced into lead‐free all‐inorganic Cs₂AgBiBr₆‐based perovskite solar cells to enhance the efficiency and stability by broadening the absorption spectrum, promoting the charge carrier separation/extraction and constructing an appropriate energy level alignment. As a result, the optimized device shows a superior power conversion efficiency of 2.84% and excellent operational stability under ambient conditions.

Abstract

Perovskite solar cells (PSCs) are highly promising next‐generation photovoltaic devices because of the cheap raw materials, ideal band gap of ≈1.5 eV, broad absorption range, and high absorption coefficient. Although lead‐based inorganic‐organic PSC has achieved the highest power conversion efficiency (PCE) of 25.2%, the toxic nature of lead and poor stability strongly limits the commercialization. Lead‐free inorganic PSCs are potential alternatives to toxic and unstable organic‐inorganic PSCs. Particularly, double‐perovskite Cs₂AgBiBr₆‐based PSC has received interests for its all inorganic and lead‐free features. However, the PCE is limited by the inherent and extrinsic defects of Cs₂AgBiBr₆ films. Herein, an effective and facile strategy is reported for improving the PCE and stability by introducing an N719 dye interlayer, which plays multifunctional roles such as broadening the absorption spectrum, suppressing the charge carrier recombination, accelerating the hole extraction, and constructing an appropriate energy level alignment. Consequently, the optimizing cell delivers an outstanding PCE of 2.84%, much improved as compared with other Cs₂AgBiBr₆‐based PSCs reported so far in the literature. Moreover, the N719 interlayer greatly enhances the stability of PSCs under ambient conditions. This work highlights a useful strategy to boost the PCE and stability of lead‐free Cs₂AgBiBr₆‐based PSCs simultaneously, accelerating the commercialization of PSC technology.

CsBr/KBr‐additive‐assisted all‐inorganic perovskite quantum dots demonstrate reduced nonradiative recombination paths and improved carrier transport. The as‐fabricated self‐powered flexible photodetector arrays exhibit superior photoresponse and electrical stability under different bending conditions (60° and 1600 cycles) with marginal degradation. Moreover, uniform photoresponse is achieved in photodetector arrays, promising for photosensing and imaging systems.

Abstract

Flexible devices are garnering substantial interest owing to their potential for wearable and portable applications. Here, flexible and self‐powered photodetector arrays based on all‐inorganic perovskite quantum dots (QDs) are reported. CsBr/KBr‐mediated CsPbBr₃ QDs possess improved surface morphology and crystallinity with reduced defect densities, in comparison with the pristine ones. Systematic material characterizations reveal enhanced carrier transport, photoluminescence efficiency, and carrier lifetime of the CsBr/KBr‐mediated CsPbBr₃ QDs. Flexible photodetector arrays fabricated with an optimum CsBr/KBr treatment demonstrate a high open‐circuit voltage of 1.3 V, responsivity of 10.1 A W⁻¹, specific detectivity of 9.35 × 10¹³ Jones, and on/off ratio up to ≈10⁴. Particularly, such performance is achieved under the self‐powered operation mode. Furthermore, outstanding flexibility and electrical stability with negligible degradation after 1600 bending cycles (up to 60°) are demonstrated. More importantly, the flexible detector arrays exhibit uniform photoresponse distribution, which is of much significance for practical imaging systems, and thus promotes the practical deployment of perovskite products.

The study presents the curious case of ionic defect migration in halide perovskites. Using photoluminescence in samples of different grain sizes coupled with molecular dynamic simulation, this study highlights the light‐induced ionic defect movement in relation to the material microstructure. In particular, it is shown that ionic defect migration is blocked by grain boundaries in methylammonium lead iodide perovskite.

Abstract

Halide perovskites are emerging as revolutionary materials for optoelectronics. Their ionic nature and the presence of mobile ionic defects within the crystal structure have a dramatic influence on the operation of thin‐film devices such as solar cells, light‐emitting diodes, and transistors. Thin films are often polycrystalline and it is still under debate how grain boundaries affect the migration of ions and corresponding ionic defects. Laser excitation during photoluminescence (PL) microscopy experiments leads to formation and subsequent migration of ionic defects, which affects the dynamics of charge carrier recombination. From the microscopic observation of lateral PL distribution, the change in the distribution of ionic defects over time can be inferred. Resolving the PL dynamics in time and space of single crystals and thin films with different grain sizes thus, provides crucial information about the influence of grain boundaries on the ionic defect movement. In conjunction with experimental observations, atomistic simulations show that defects are trapped at the grain boundaries, thus inhibiting their diffusion. Hence, with this study, a comprehensive picture highlighting a fundamental property of the material is provided while also setting a theoretical framework in which the interaction between grain boundaries and ionic defect migration can be understood.

Different concentrations of iridium complexes are introduced into the conjugated backbone of polymer donor PM6 (PM6‐Ir0), this strategy can rationally modify the molecular aggregations, effectively control the blend morphology and physical mechanisms, and finally improve the photovoltaic performance. This work affords an effective approach for further breakthroughs in the reported champion power conversion efficiency of polymer solar cells.

Abstract

The commercially available PM6 as donor materials are used widely in highly efficient nonfullerene polymer solar cells (PSCs). In this work, different concentrations of iridium (Ir) complexes (0, 0.5, 1, 2.5, and 5 mol%) are incorporated carefully into the polymer conjugated backbone of PM6 (PM6‐Ir0), and a set of π‐conjugated polymer donors (named PM6‐Ir0.5, PM6‐Ir1, PM6‐Ir2.5, and PM6‐Ir5) are synthesized and characterized. It is demonstrated that the approach can rationally modify the molecular aggregations of polymer donors, effectively controlling the corresponding blend morphology and physical mechanisms, and finally improve the photovoltaic performance of the PM6‐Irx‐based PSCs. Among them, the best device based on PM6‐Ir1:Y6 (1:1.2, w/w) exhibits outstanding power conversion efficiencies (PCEs) of 17.24% tested at Wuhan University and 17.32% tested at Institute of Chemistry, Chinese Academy of Sciences as well as a certified PCE of 16.70%, which are much higher than that of the control device based on the PM6‐Ir0:Y6 blend (15.39%). This work affords an effective approach for further break through the reported champion PCE of the binary PSCs.

Herein, a novel precursor (HCOOCs and HPbX₃) for deposition of high‐quality CsPbI₂Br films, irrespective of humidity is presented. CsPbI₂Br cells prepared in an atmosphere with 30% and 91% relative humidity exhibit efficiencies of 16.1% and 15.1%, respectively, which are the highest among all inorganic CsPbX₃ (X: I, Br, or mixed halides) PSCs prepared in a medium or high humid atmosphere.

Abstract

High temperature stable inorganic CsPbX₃ (X: I, Br, or mixed halides) perovskites with their bandgap tailored by tuning the halide composition offer promising opportunities in the design of ideal top cells for high‐efficiency tandem solar cells. Unfortunately, the current high‐efficiency CsPbX₃ perovskite solar cells (PSCs) are prepared in vacuum, a moisture‐free glovebox or other low‐humidity conditions due to their poor moisture stability. Herein, a new precursor system (HCOOCs, HPbI₃, and HPbBr₃) is developed to replace the traditional precursors (CsI, PbI₂, and PbBr₂) commonly used for solar cells of this type. Both the experiments and calculations reveal that a new complex (HCOOH•Cs⁺) is generated in this precursor system. The new complex is not only stable against aging in humid air ambient at 91% relative humidity, but also effectively slows the perovskite crystallization, making it possible to eliminate the popular antisolvent used in the perovskite CsPbI₂Br film deposition. The CsPbI₂Br PSCs based on the new precursor system achieve a champion efficiency of 16.14%, the highest for inorganic PSCs prepared in ambient air conditions. Meanwhile, high air stability is demonstrated for an unencapsulated CsPbI₂Br PSC with 92% of the original efficiency remaining after more than 800 h aging in ambient air.

In situ optical spectroscopy during two‐step deposition of narrow bandgap Pb–Sn hybrid perovskite films reveals the film formation kinetics. Homogeneous crystallization and passivation of iodide vacancies on the perovskite surface gives solar cells with a power conversion efficiency of 16.1% at a bandgap of 1.23 eV.

Abstract

Developing efficient narrow bandgap Pb–Sn hybrid perovskite solar cells with high Sn‐content is crucial for perovskite‐based tandem devices. Film properties such as crystallinity, morphology, surface roughness, and homogeneity dictate photovoltaic performance. However, compared to Pb‐based analogs, controlling the formation of Sn‐containing perovskite films is much more challenging. A deeper understanding of the growth mechanisms in Pb–Sn hybrid perovskites is needed to improve power conversion efficiencies. Here, in situ optical spectroscopy is performed during sequential deposition of Pb–Sn hybrid perovskite films and combined with ex situ characterization techniques to reveal the temporal evolution of crystallization in Pb–Sn hybrid perovskite films. Using a two‐step deposition method, homogeneous crystallization of mixed Pb–Sn perovskites can be achieved. Solar cells based on the narrow bandgap (1.23 eV) FA_0.66MA_0.34Pb_0.5Sn_0.5I₃ perovskite absorber exhibit the highest efficiency among mixed Pb–Sn perovskites and feature a relatively low dark carrier density compared to Sn‐rich devices. By passivating defect sites on the perovskite surface, the device achieves a power conversion efficiency of 16.1%, which is the highest efficiency reported for sequential solution‐processed narrow bandgap perovskite solar cells with 50% Sn‐content.

This review focuses on the usefulness of spatially resolved analysis of halide perovskite solar cells. Methods sensitive to open circuit voltage, short circuit current, fill factor, and cell efficiency are discussed, and the specific value of the spatial information is demonstrated in quantitative loss analyses.

Abstract

This review explores the current state of the art in spatially resolved characterization of mixed‐halide perovskite solar cells. As the size of perovskite cells and modules continues to grow, quantification of the spatial distribution of key cell parameters will become increasingly valuable in predicting ultimate cell‐level performance and tracking process homogeneity. Here, both high resolution microscopic approaches using scanning techniques and camera‐based methods for full‐area cell and/or module analysis are discussed. The value of this local data in predicting performance losses at the cell level is particularly emphasized. Measurable physical parameters sensitive to losses of voltage, current, fill factor, and efficiency are discussed together with selected experimental results. It is demonstrated that a combination of spatially resolved cell parameter mapping/imaging can be used to quantitatively discriminate various loss contributions at high resolution. The impact and control of inhomogeneities become particularly important when upscaling from small devices to large formats compatible with industrial mass production.

The highest power conversion efficiency of the perovskite solar cells based on poly (3‐hexylthiophene)/gold nanorod (P3HT/AuNR) composite hole‐transporting material reaches up to 16.88%, which is higher than that of a pristine P3HT‐based device (13.40%). The enhancement can be attributed to the higher carrier mobility and increased light utilization efficiency induced by addition of AuNRs with localized surface plasmon resonance effect in the polymer matrix.

Poly(3‐hexylthiophene)/gold nanorod (P3HT/AuNR) composites are developed and introduced as hole‐transporting materials (HTMs) to fabricate mixed‐ion perovskite solar cells (PSCs). The highest power conversion efficiency of the optimized devices based on the composite HTM reaches up to 16.88%, which is an increase of 26% from that of a pristine P3HT‐based device (13.40%). The enhanced performance can be attributed to the increased crystallinity of P3HT induced by the addition of AuNRs in the polymer matrix and the localized surface plasmon resonance effect of AuNRs, which lead to higher carrier mobility and increased light utilization efficiency. This work provides a comprehensive understanding of the effect of plasmonic AuNRs in PSCs application and a useful method to further improve the performance of PSCs.

The A‐site incorporation in the all‐inorganic cesium lead mixed halide (CsPbI₂Br) perovskite facilitates thermodynamic stability. The Rb cation‐incorporated Cs_1−x M _x PbI₂Br (M = Rb)‐based perovskite absorber layer processed by hot air method under ambient conditions with additives doped poly(3‐hexylthiophene‐2,5‐diyl) as a hole‐transporting layer produces a power conversion efficiency of more than 17%.

Due to its excellent thermal stability and high performance, inorganic cesium lead mixed halide (ABX₃, where A  = Cs, B = Pb, and X = I/Br) all‐inorganic perovskite solar cells (IPVSCs) have attracted much interest in optoelectronic applications. However, the film quality, enough absorption by desired film thickness, and nature of partial replacement of cations determine the stability of the CsPbI₂Br perovskite films. Herein, a hot air method is used to control the thickness and morphology of the CsPbI₂Br perovskite thin film, and the A‐site (herein, Cs⁺) cation is partially incorporated by rubidium (Rb⁺) cations for making the stable black phase under ambient conditions. The Rb cation‐incorporated Cs_1−x Rb _x PbI₂Br (x  = 0–0.03) perovskite thin films exhibit high crystallinity, uniform grains, extremely dense, and pinhole‐free morphology. The fabricated device with its Cs_0.99Rb_0.01PbI₂Br perovskite composition with poly(3‐hexylthiophene‐2,5‐diyl) as a hole‐transporting layer exhibits a power conversion efficiency (PCE) of 17.16%, which is much higher than that of CsPbI₂Br‐based IPVSCs. The fabricated Cs_0.99Rb_0.01PbI₂Br‐based IPVSC devices retain >90% of the initial efficiency over 120 h at 65 °C thermal stress, which is much higher than that of CsPbI₂Br samples.

Methylammonium thiocyanate additive‐assisted hot‐casting free deposition of a high‐quality 2D Dion–Jacobson perovskite film is reported. The optimized film exhibits high crystallinity, preferred orientation, and decreased defects. The corresponding device exhibits a maximum power conversion efficiency of 16.25%. The unsealed device retains 80% of its original efficiency after 35 days of storage in air with a humidity level of 45 ± 5%.

2D Dion–Jacobson (DJ) perovskite solar cells (PVSCs) with a high power conversion efficiency (PCE) are currently predominately fabricated via a hot‐casting process. The reason lies in the difficulty in preparing high‐quality perovskite films under mild conditions when the application of divalent ammonium removes the weak interaction from the spacer cation layer. Herein, the morphology of the 2D DJ perovskite film with a rigid piperidinium ring is tuned through a room‐temperature spin‐coating method, with the aid of a methylammonium thiocyanate (MASCN) additive. With the optimized amount of MASCN addition, the perovskite films deposited on the poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA)/poly[(9,9‐bis(30‐(N ,N‐dimethylamino)propyl)‐2,7‐uorene)‐alt‐2,7‐(9,9‐dioctylfuorene)] (PFN) substrate exhibit fine crystallinity, preferred orientation, decreased defects, and better energy‐level alignment with the hole transport layer. The device with the inverted planar structure presents a J _SC of 17.91 mA cm⁻², V _OC of 1.19 V, fill factor of 0.76, with a maximum PCE of 16.25%, which is the highest PCE for 2D DJ PVSCs free of hot casting. The unsealed device maintains around 80% of its initial efficiency after 35 days of exposure to air (Hr = 45 ± 5%). A potential route toward high‐performance 2D DJ PVSCs is provided.

The significant energy loss in organic solar cells mainly results from the charge transfer loss and the nonradiative recombination loss. In view of this, herein, the recent advances in energy loss reduction according to different strategies are systematically summarized. On this basis, some fundamental questions in this topic are proposed to improve future investigations.

Compared with conventional inorganic solar cells (ISCs), energy loss (E _loss) in organic solar cells (OSCs) is usually much higher, limiting their maximum achievable power conversion efficiency (PCE). In view of this, a hot topic in OSC research is how to make E _loss as low as possible. To date, in some typical organic donor/acceptor (D/A) blends, although E _loss has been reduced to the values comparable with those in ISCs, the PCEs of the corresponding devices still fails to meet expectations. One crucial issue is that the physics behind the photovoltaic process in these D/A blends and the corresponding energy loss remain unclear. Herein, combining with an analysis of the photovoltaic process in OSCs, the mechanisms of different energy loss pathways are first discussed. On this basis, the recent advances focusing on E _loss are systematically summarized according to different strategies: 1) optimizing the energy offset of the D/A blend; 2) optimizing the morphology of the D/A blend; 3) ternary modulation; and 4) spin modulation. Finally, the summary and prospects are presented, where some fundamental questions to be cleared up in the photovoltaic process are proposed, such that more targeted photovoltaic design can be carried out in the future investigations of OSCs.

The effects of topography and electrical signals on neural differentiation of stem cells are discussed. Co‐effects of topography/electrical cues on stem cell differentiation are also reviewed, and previous studies on conductive and patterned scaffolds are summarized.

Abstract

Incomplete regeneration and restoration of function in damaged nerves is a major clinical challenge. In this regard, stem cells hold much promise in nerve tissue engineering, with advantages such as prevention of scar‐tissue ingrowth and guidance of axonal regrowth. Engineering 3D and patterned microenvironments using biomaterials with chemical and mechanical characteristics close to those of normal nervous tissue has enabled new approaches for guided differentiation of various stem cells toward neural cells and possible treatment of neurodegenerative diseases such as Alzheimer's, Parkinson's, and Huntington's diseases. Differentiation of stem cells in a neurogenic lineage is largely affected by signals from the surrounding microenvironment (niche). The stem cell niche refers to a specific microenvironment around the stem cells, which provides specific biochemical (soluble factors) and biophysical signals (topography, electrical, and mechanical). This specified niche regulates the stem cells' behavior and fate. While the role of chemical cues in neural differentiation is well appreciated, recently, the cues presented by the physical microenvironment are increasingly documented to be important regulators of nerve cell differentiation. The single and synergistic effects of surface topography and electrical signals on neural differentiation of stem cells are reviewed.

Herein, 17% efficient and stable ternary organic solar cells are realized by introducing a delayed fluorescence material 3,4‐bis(4‐(diphenylamino)phenyl)acenaphtho[1,2‐b]pyrazine‐8,9‐dicarbonitrile (APDC‐TPDA) in a non‐fullerene system. Long‐lifetime singlet excitons on APDC‐TPDA can transfer to the polymer donor to prolong the excitons lifetime and suppress the reverse energy transfer from charge transfer state to triplet state, and then reduce the recombination energy loss of the device.

Abstract

Charge transfer state (CT) plays an important role in exciton diffusion, dissociation, and charge recombination mechanisms. Enhancing the utilization and suppressing the recombination process of CT excitons is a promising way to improve the performance of organic solar cells (OSCs). Here, an effective method is presented via introducing a delayed fluorescence (DF) emitter 3,4‐bis(4‐(diphenylamino)phenyl)acenaphtho[1,2‐b]pyrazine‐8,9‐dicarbonitrile (APDC‐TPDA) in OSCs. The long‐lifetime singlet excitons on APDC‐TPDA can transfer to polymer donors to prolong exciton lifetime, which ensures sufficient time for diffusion and dissociation. Concurrently, the high triplet energy level (T₁) of the DF material can also prevent the reverse energy transfer from CT to T₁. APDC‐TPDA‐containing ternary OSCs shows a high PCE of 16.96% with a reduced recombination energy loss of 0.46 eV. It is noteworthy that the ternary OSC also exhibits superior storage stability. After 55 days of storage, the PCE of the ternary OSC still retains about 96% of its primitive state. Furthermore, this ternary strategy is efficient and universally applicable to OSCs, and positive results can be obtained in different systems with different DF emitters. These results indicate that the ternary strategy provides a new design idea to realize high performance OSCs.

Graphitic carbon nitride (g‐C₃N₄) is doped into PEDOT:PSS to improve the conductivity by weakening the shield effect of PSS on conductive PEDOT. Employing g‐C₃N₄ doped PEDOT:PSS as a hole transport layer for PM6:Y6‐based organic solar cells, a device efficiency of up to 16.4% is achieved, partly as a result of improved charge transport and suppressed charge recombination at the interface.

Abstract

The power‐conversion efficiency (PCE) of single‐junction organic solar cells (OSCs) has exceeded 16% thanks to the development of non‐fullerene acceptor materials and morphological optimization of active layer. In addition, interfacial engineering always plays a crucial role in further improving the performance of OSCs based on a well‐established active‐layer system. Doping of graphitic carbon nitride (g‐C₃N₄) into poly(3,4‐ethylene‐dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a hole transport layer (HTL) for PM6:Y6‐based OSCs is reported, boosting the PCE to almost 16.4%. After being added into the PEDOT:PSS, the g‐C₃N₄ as a Bronsted base can be protonated, weakening the shield effect of insulating PSS on conductive PEDOT, which enables exposures of more PEDOT chains on the surface of PEDOT:PSS core‐shell structure, and thus increasing the conductivity. Therefore, at the interface between g‐C₃N₄ doped HTL and PM6:Y6 layer, the charge transport is improved and the charge recombination is suppressed, leading to the increases of fill factor and short‐circuit current density of devices. This work demonstrates that doping g‐C₃N₄ into PEDOT:PSS is an efficient strategy to increase the conductivity of HTL, resulting in higher OSC performance.