Inorganic Solar Cells Research Articles

Interface Modification for Efficient and Stable Inverted Inorganic Perovskite Solar Cells.

Due to their excellent thermal stability and ideal bandgap, metal halide inorganic perovskite based solar cells (PSCs) with inverted structure are considered as an excellent choice for perovskite/silicon tandem solar cells. However, the power conversion efficiency (PCE) of inverted inorganic PSCs still lags far behind that of conventional n-i-p PSCs due to interfacial energy level mismatch and high nonradiative charge recombination. Herein, the performance of inverted PSCs was significantly improved by interfacial engineering of CsPbI3-x Brx films with 2-mercapto-1-methylimidazole (MMI). It is found that the mercapto group can preferably react with the undercoordinated Pb2+ from perovskite by forming Pb-S bonds, which appreciably reduces the surface trap density. Moreover, MMI modification results in a better energy level alignment with the electron transporting material, promoting carrier transfer and reducing voltage deficit. The above combination results in an open circuit voltage enhancement by 120mV, yielding a champion PCE of 20.6% for 0.09 cm2 area and 17.3% for 1 cm2 area. Furthermore, the ambient, operational and heat stabilities of inorganic PSCs with MMI modification are also greatly improved. Our work demonstrates a simple but effective approach for fabricating highly efficient and stable inverted inorganic PSCs. This article is protected by copyright. All rights reserved.

Managing Multiple Halide-Related Defects for Efficient and Stable Inorganic Perovskite Solar Cells.

Halide-related surface defects on inorganic halide perovskite not only induce charge recombination but also severely limit the long-term stability of perovskite solar cells. Herein, adopting density functional theory calculation, we verify that iodine interstitials (Ii ) has a low formation energy similar to that of the iodine vacancy (VI ) and is also readily formed on the surface of all-inorganic perovskite, and it is regarded to function as an electron trap. We screen a specific 2,6-diaminopyridine (2,6-DAPy) passivator, which, with the aid of the combined effects from halogen-Npyridine and coordination bonds, not only successfully eliminates the Ii and dissociative I2 but also passivates the abundant VI . Furthermore, the two symmetric neighboring -NH2 groups interact with adjacent halides of the octahedral cluster by forming hydrogen bonds, which further promotes the adsorption of 2,6-DAPy molecules onto the perovskite surface. Such synergetic effects can significantly passivate harmful iodine-related defects and undercoordinated Pb2+ , prolong carrier lifetimes and facilitate the interfacial hole transfer. Consequently, these merits enhance the power-conversion efficiency (PCE) from 19.6 % to 21.8 %, the highest value for this type of solar cells, just as importantly, the 2,6-DAPy-treated CsPbI3-x Brx films show better environmental stability.

Managing Multiple Halide‐Related Defects for Efficient and Stable Inorganic Perovskite Solar Cells

AbstractHalide‐related surface defects on inorganic halide perovskite not only induce charge recombination but also severely limit the long‐term stability of perovskite solar cells. Herein, adopting density functional theory calculation, we verify that iodine interstitials (Ii) has a low formation energy similar to that of the iodine vacancy (VI) and is also readily formed on the surface of all‐inorganic perovskite, and it is regarded to function as an electron trap. We screen a specific 2,6‐diaminopyridine (2,6‐DAPy) passivator, which, with the aid of the combined effects from halogen‐Npyridine and coordination bonds, not only successfully eliminates the Ii and dissociative I2 but also passivates the abundant VI. Furthermore, the two symmetric neighboring ‐NH2 groups interact with adjacent halides of the octahedral cluster by forming hydrogen bonds, which further promotes the adsorption of 2,6‐DAPy molecules onto the perovskite surface. Such synergetic effects can significantly passivate harmful iodine‐related defects and undercoordinated Pb2+, prolong carrier lifetimes and facilitate the interfacial hole transfer. Consequently, these merits enhance the power‐conversion efficiency (PCE) from 19.6 % to 21.8 %, the highest value for this type of solar cells, just as importantly, the 2,6‐DAPy‐treated CsPbI3−xBrx films show better environmental stability.

Optimization of Electron Transport Layer‐Free Cs2TiBr6/MASnBr3 Laminated Structure Perovskite Solar Cells by SCAPS‐1D Simulation

Cs2TiBr6 materials have promising applications in organic–inorganic halide perovskite solar cells (PSCs), but their power conversion efficiency (PCE) is low. Herein, based on the matching band structure of MASnBr3 and Cs2TiBr6, a no‐electron transport layer (ETL)‐structured laminated PSC is constructed for numerical simulation using SCAPS‐1D. The results have shown that the ETL‐free structure reduces the potential barrier between the interfaces and improves the performance of the device. MASnBr3 is used to replace the traditional hole transport layer to form a laminated structure, which is more conducive to the built‐in electric field of the device. Through exploring the internal influencing factors and applicable environment, it is found that the device can maintain a good operating level between 230 and 430 K. Finally, the best PCE of 19.63% is achieved in the proposed device structure (FTO/Cs2TiBr6/MASnBr3/Au). This work provides a new approach to achieving lead‐free and efficient laminated PSCs in a wide temperature range of usage environments from −43 to 157 °C.

Enhancement of Photoelectric Performance Based on Ultrathin Wide Spectrum Solar Absorption in Cruciform Microstructure Germanium Solar Cells

In this paper, the solar absorption level of PEDOT:PSS/Ge organic and inorganic hybrid solar cells (HSCs) with different parameters of cruciform microstructure (CM) is studied, using the finite-difference time domain (FDTD) method. The light absorption in HSCs with CM is above 90% in the range of 300 nm to 1300 nm. Under the AM1.5 solar spectrum, the average absorptivity of solar energy is also at a very high level. At the same time, we use DEVICE software to calculate the electrical properties, such as the open-circuit voltage (Voc), short-circuit current density (Jsc), and maximum power density (Pmax). The electrical simulation results show that the Pmax of HSCs with CM improves to 72.16% from the planar HSCs. Besides, in order to study the mechanism of solar energy absorption in HSCs containing CM, the logarithmic plots of electric field intensity of HSCs with CM and planar HSCs, are analyzed at different wavelengths. The work shows that the CM shows an excellent light-trapping effect, which reduces the surface reflectivity of HSCs, and greatly improves the photoelectric conversion efficiency of Ge solar cells.

Recent Advances in Functionalized Fullerenes in Perovskite Solar Cells†

Comprehensive SummaryEfficient charge transport and defect passivation are essential for high efficiency of organic–inorganic hybrid perovskite solar cells (PSCs). Functionalized fullerenes featuring high electron affinity and mobility as well as small reorganization energy have been extensively applied in PSCs toward facilitated electron transport and passivated trap states, leading to improvements of both device efficiency and stability. Herein, we summarize the recent advances, especially in the last three years, in applications of functionalized fullerenes including fullerene derivatives and endohedral metallofullerenes in PSCs. Their functions in trap state passivation, electron transport promotion, crystalline modulation, water/oxygen erosion inhibition, and so on, are discussed in details. In particular, we emphasize novel functions of fullerenes beyond trap state passivation, as well as the synergy of multifunction of fullerenes in improving PSC device performance and stability. Finally, we present an outlook on designing novel multifunctionalized fullerenes toward highly efficient and stable PSC devices.

Lead free CsSn0.5Ge0.5I3 perovskite solar cell with different layer properties via SCAPS‐1D simulation

AbstractOrganic–inorganic halide perovskite solar cells (PSCs) have been extensively studied due to their simple fabrication methods and obvious device efficiency advantages. In this work, the perovskite CsSn0.5Ge0.5I3 is used as the light absorption layer, which is doped with Ge2+ in CsSnI3 to improve its stability. The polymers of 3‐hexylthiophene (P3HT) with excellent optoelectronic properties and low price, and SnO2 with high electron extraction ability is selected as charge transport layers. Based on these, a novel PSC structure (FTO/SnO2/IDL1/CsSn0.5Ge0.5I3/IDL2/P3HT/Au) has been simulated via solar cell capacitor simulator (SCAPS‐1D). The PSC performance is optimized by adjusting a series of parameters, including the layer thickness, defect density, electron affinity potential energy, and operating temperature, and so forth. The results show that the PSC defects are passivated by adjusting the appropriate parameters, and the final optimized open circuit voltage (VOC) is 1.08 V, short‐circuit current density (JSC) is 27.37 mA/cm2, fill factor (FF) is 83.32%, while the power conversion efficiency (PCE) is increased from the initial 10.89% to 24.63%, which provides theoretical reference for experiments and new ideas for the preparation and development of efficient and environmentally friendly PSCs. Finally, the effect of different metal cathodes with and without hole transport layer (HTL) on PSC performance is compared. The PSCs without HTL are more dependent on battery cathodes, which provided a way to replace precious metals with other electrode materials.

Role of Dibenzo Crown Additive for Improving the Stability of Inorganic Perovskite Solar Cells.

Photovoltaics are being transformed by perovskite solar cells. The power conversion efficiency of these solar cells has increased significantly, and even higher efficiencies are possible. The scientific community has gained much attention due to perovskites' potential. Herein, the electron-only devices were prepared by spin-coating and introducing the organic molecule dibenzo-18-crown-6 (DC) to CsPbI2Br perovskite precursor solution. The current-voltage (I-V) and J-V curves were measured. The morphologies and elemental composition information of the samples were obtained by SEM, XRD, XPS, Raman, and photoluminescence (PL) spectroscopies. The distinct impact of organic DC molecules on the phase, morphology, and optical properties of perovskite films are examined and interpreted with experimental results. The efficiency of the photovoltaic device in the control group is 9.76%, and the device efficiency gradually increases with the increase of DC concentration. When the concentration is 0.3%, the device efficiency is the best, reaching 11.57%, short-circuit current is 14.01 mA/cm2, the open circuit voltage is 1.19 V, and the fill factor is 0.7. The presence of DC molecules effectively controlled the perovskite crystallization process by inhibiting the in-situ generations of impurity phases and minimizing the defect density of the film.

Controlled crystallization and surface engineering of mixed-halide γ-CsPbI2Br inorganic perovskites via guanidinium iodide additive in air-processed perovskite solar cells

In this report, we demonstrate enlarged grain size (up to ∼3 μm) in ambient-stable black γ-phase CsPbI2Br thin films through the regulated addition of guanidinium iodide (GAI) as an effective volatile additive. Nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) measurements indicate the complete sublimation of GAI following annealing, with no inclusion inside the final γ-CsPbI2Br perovskite lattice. GAI is found to participate by retarding the cation–anion reaction via the Cs+ and GA+ cation-exchange process. We find that inorganic perovskite solar cells (IPSCs) devices made from (CsPbI2Br)0.925 + 0.075 GAI and a phenyltrimethylammonium chloride (PTACl) passivation retain a solar-friendly band-gap of 1.91 eV and excellent device performance, with the best open-circuit voltage reaching as high as 1.34 V, with highly reproducible and stable photo conversion efficiencies of 16.88% (for 0.09 cm2) and 15.60% (large area 1 cm2) under ambient conditions. Photostability analysis further demonstrated negligible efficiency loss over 1000 h under continuous one-sun equivalent illumination, indicating GAI additive as a promising approach toward ambient stable, all-inorganic high-efficiency solar cells.

Combination of Poly(3-butylthiophene) Hole-Transporting Layer and Butylammonium Interface Passivation to Improve an Inorganic Perovskite Solar Cell

Owing to their superior power conversion efficiencies (PCEs), all-perovskite tandem solar cells have recently attracted extensive attention, in which an inorganic CsPbI2Br perovskite with a wide band gap is configurated as the front photovoltaic cell. A dopant-free poly(3-butylthiophene) is an effective hole-extracting and -transporting material coated on the inorganic perovskite layer, compared with conventional poly(3-hexyl- and -octyl-thiophene)s. In addition, surface passivation of the perovskite layer using alkyl ammonium bromide, especially butyl-one, further improves the PCE, including its durability. Herein, we discussed the matching of the alkyl chain lengths for poly(3-alkylthiophene) and of the alkyl ammonium salt at the interface of the hole-extracting and passivated perovskite layers.

Inorganic Perovskite Surface Reconfiguration for Stable Inverted Solar Cells with 20.38% Efficiency and Its Application in Tandem Devices.

Inorganic perovskite solar cells (IPSCs) have garnered attention in tandem solar cells (TSCs) due to their suitable bandgap and impressive thermal stability. However, the efficiency of inverted IPSCs has been limited by the high trap density on the top surface of inorganic perovskite film. Herein, a method for fabricating efficient IPSCs by reconfiguring the surface properties of CsPbI2.85 Br0.15 film with 2-amino-5-bromobenzamide (ABA) is developed. This modification not only exhibits the synergistic coordination of carbonyl (C=O) and amino (NH2 ) groups with uncoordinated Pb2+ , but also the Br fills halide vacancies and suppresses the formation of Pb0 , effectively passivating the defective top surface. As a result, a champion efficiency of 20.38%, the highest efficiency reported for inverted IPSCs to date is achieved. Furthermore, the successful fabrication of a p-i-n type monolithic inorganic perovskite/silicon TSCs with an efficiency of 25.31% for the first time is demonstrated. Crucially, the unencapsulated ABA-treated IPSCs shows enhanced photostability, retaining 80.33% of its initial efficiency after 270h, and thermal stability (maintain 85.98% of its initial efficiency after 300h at 65°C). The unencapsulated ABA-treated TSCs also retains 92.59% of its initial efficiency after 200h under continuous illumination in ambient air.

First-Principles Predictions of Structural, Mechanical, and Optoelectronic Properties of Se-Based Double Perovskites A2SeX6 (A = Rb, K; X = Cl, Br, I)

The toxicity of lead and the instability of lead-based perovskite materials in the air are two key challenges in emerging Pb-based inorganic perovskite solar cells. Thus, the development of lead-free and stabilized inorganic perovskite materials is of great interest. In this work, the structural, ductility, and optoelectronic properties of Se-based double perovskites A2SeX6 (A = Rb, K; X = Cl, Br, I) have been studied for the first time by first-principles calculations to determine their potential use in optoelectronic sectors. Results reveal that these new series of A2SeX6 (A = Rb, K; X = Cl, Br, I) double perovskites are structural and mechanical stability. Their ductility increases as the halogen atom goes from Cl to I. Especially, the K2SeI6 possesses better ductility than other double perovskites. Electronic structure calculations exhibit that these new perovskite compounds are indirect band gap semiconductors. The Rb2SeI6 and K2SeI6 have more suitable bandgaps (1.24 and 1.16 eV) and smaller carrier masses, which are suitable for absorber layers of solar cells, while A2SeCl6 and A2SeBr6 are suitable for fabricating the optoelectronic devices in the ultraviolet region due to the wide gap. Furthermore, all these A2SeX6 compounds exhibit excellent optical properties with light absorption coefficients over 105 cm–1. Especially, the Rb2SeI6 and K2SeI6 have more excellent absorption spectra throughout the whole visible region. These results show that both Rb2SeI6 and K2SeI6 are potential candidates for absorption layer materials of solar cells, and A2SeCl6 and A2SeBr6 are suitable for other optoelectronic devices, such as photodetectors, light-emitting diodes, and so on.

Liquid buried interface to slide lattice and heal defects in inorganic perovskite solar cells

The residual tensile strain, which is induced by lattice and thermal expansion coefficient difference between upper perovskite film and underlying charge transporting layer, significantly deteriorates the power conversion efficiency (PCE) and stability of a halide perovskite solar cell (PSC). To overcome this technical bottleneck, herein, we propose a universal liquid buried interface (LBI) by introducing a low melting-point small molecule to replace traditional solid–solid interface. Arising from the movability upon solid-to-liquid phase conversion, LBI plays a role of “lubricant” to effectively free the soft perovskite lattice shrinkage or expansion rather than anchoring onto the substrate, leading to the reduced defects due to the healing of strained lattice. Finally, the inorganic CsPbIBr2 PSC and CsPbI2Br cell achieve the best PCEs of 11.13 % and 14.05 %, respectively, and the photo-stability is improved by 33.3-fold because of the suppressed halide segregation. This work provides new insights on the LBI for making high-efficiency and stable PSC platforms.

Improve Perovskite Solar Cell Stability and Efficiency via Multifunctional Multiple‐Ring Aromatic Dopant Passivation

Organic–inorganic perovskite solar cells, as a representative of the new generation of solar cells, have made satisfactory advancements in development over the past few years. However, the low carrier transport characteristics and energy loss brought on by defects severely restrict its development. This study develops a new liquid crystal material 1‐naphthalene acetic acid potassium salt (C12H9KO2, K‐NAA) as a dopant into the MA0.6FA0.4PbI3−xClx material. The presence of free K+ ions in K‐NAA modifies the perovskite lattice gap, and the CO structure can efficiently passivate the Pb2+ defect caused by the absence of coordination. Therefore, the grain boundaries, which serve as points of moisture penetration become blurred, hence suppressing charge trapping/recombination centers and enhancing the film quality and stability. The naphthalene in K‐NAA has a conjugated multiple‐ring aromatic structure. The abundant π‐electron delocalization present in the conjugated structure of the benzene ring may provide an electron‐rich environment outside the connected crystal structure, resulting in field‐effect passivation and effectively enhancing carrier transport performance. Hence, the devices deliver a champion power conversion efficiency (PCE) of 19.86%. After 700 h under the dark at 25 °C and 30% humidity, the optimized unencapsulated device PCE maintains at 92% of its initial efficiency.

Performance Optimization of CsPb(I1–xBrx)3 Inorganic Perovskite Solar Cells with Gradient Bandgap

In recent years, inorganic perovskite solar cells (PSCs) based on CsPbI3 have made significant progress in stability compared to hybrid organic–inorganic PSCs by substituting the volatile organic component with Cs cations. However, the cubic perovskite structure of α-CsPbI3 changes to the orthorhombic non-perovskite phase at room temperature resulting in efficiency degradation. The partial substitution of an I ion with Br ion benefits for perovskite phase stability. Unfortunately, the substitution of Br ion would enlarge bandgap reducing the absorption spectrum range. To optimize the balance between band gap and stability, introducing and optimizing the spatial bandgap gradation configuration is an effective method to broaden the light absorption and benefit the perovskite phase stability. As the bandgap of the CsPb(I1–xBrx)3 perovskite layer can be adjusted by I-Br composition engineering, the performance of CsPb(I1–xBrx)3 based PSCs with three different spatial variation Br doping composition profiles were investigated. The effects of uniform doping and gradient doping on the performance of PSCs were investigated. The results show that bandgap (Eg) and electron affinity(χ) attributed to an appropriate energy band offset, have the most important effects on PSCs performance. With a positive conduction band offset (CBO) of 0.2 eV at the electron translate layer (ETL)/perovskite interface, and a positive valence band offset (VBO) of 0.24 eV at the hole translate layer (HTL)/perovskite interface, the highest power conversion efficiency (PCE) of 22.90% with open–circuit voltage (VOC) of 1.39 V, short–circuit current (JSC) of 20.22 mA/cm2 and filling factor (FF) of 81.61% was obtained in uniform doping CsPb(I1–xBrx)3 based PSCs with x = 0.09. By carrying out a further optimization of the uniform doping configuration, the evaluation of a single band gap gradation configuration was investigated. By introducing a back gradation of band gap directed towards the back contact, an optimized band offset (front interface CBO = 0.18 eV, back interface VBO = 0.15 eV) was obtained, increasing the efficiency to 23.03%. Finally, the double gradient doping structure was further evaluated. The highest PCE is 23.18% with VOC close to 1.44 V, JSC changes to 19.37 mA/cm2 and an FF of 83.31% was obtained.

Interface Engineering in Perylene Diimide-Based Organic Photovoltaics with Enhanced Photovoltage

The introduction of nonfullerene acceptors (NFA) facilitated the realization of high-efficiency organic solar cells (OSCs); however, OSCs suffer from relatively large losses in open-circuit voltage (VOC) as compared to inorganic or perovskite solar cells. Further enhancement in power conversion efficiency requires an increase in VOC. In this work, we take advantage of the high dipole moment of twisted perylene-diimide (TPDI) as a nonfullerene acceptor (NFA) to enhance the VOC of OSCs. In multiple bulk heterojunction solar cells incorporating TPDI with three polymer donors (PTB7-Th, PM6 and PBDB-T), we observed a VOC enhancement by modifying the cathode with a polyethylenimine (PEIE) interlayer. We show that the dipolar interaction between the TPDI NFA and PEIE─enhanced by the general tendency of TPDI to form J-aggregates─plays a crucial role in reducing nonradiative voltage losses under a constant radiative limit of VOC. This is aided by comparative studies with PM6:Y6 bulk heterojunction solar cells. We hypothesize that incorporating NFAs with significant dipole moments is a feasible approach to improving the VOC of OSCs.

CsPbI3 Based All‐Inorganic Perovskite Solar Cells: Further Performance Enhancement of the Electron Transport Layer‐Free Structure from Device Simulation

Abstract Cesium lead iodide (CsPbI3) has attracted a great deal of attention as an absorption layer material for perovskite solar cells (PSCs) with high stability and suitable band gap (1.72 eV). In response to the problems of defect‐induced nonradiative compounding and voltage loss caused by the common perovskite layer, the common strategies of interfacial engineering, altering crystal equivalence, and other modifications involve more complex processes and higher fabrication costs. In order to simplify the process and save costs, this work has omitted the electron transport layer (ETL), while still maintaining a high power conversion efficiency (PCE). This work has simulated PSCs with CsPbI3 (electron transport layer free) and have matched Cu2O as the most suitable hole transport layer (HTL) material. By simulating and optimizing the thickness and defect density of perovskite absorption layer and the defect density of interface defect layer (IDL1, IDL2), and determining the most suitable operating temperature, the PCE of the device can reach 18.8%, which is consistent with the experimental data. The asymmetric effect of the interface defect layer obtained in this work is similar to previous research reports. This research provides an economical solution for high‐performance inorganic perovskite solar cells.

Amorphous BaTiO3 Electron Transport Layer for Thermal Equilibrium‐Governed γ‐CsPbI3 Perovskite Solar Cell with High Power Conversion Efficiency of 19.96%

Compared to organic–inorganic hybrid perovskites, the cesium‐based all‐inorganic lead halide perovskite (CsPbI3) is a promising light absorber for perovskite solar cells owing to its higher resistance to thermal stress. Nonetheless, additional research is required to reduce the nonradiative recombination to realize the full potential of CsPbI3. Here, the diffusion of Cs ions participating in ion exchange is proposed to be an important factor responsible for the bulk defects in γ‐CsPbI3 perovskite. Calculations based on first‐principles density functional theory reveal that the [PbI6]4− octahedral tilt modifies the perovskite crystallographic properties in γ‐CsPbI3, leading to alterations in its bandgap and crystal strain. In addition, by substituting amorphous barium titanium oxide (a‐BaTiO3) for TiO2 as the electron transport layer, interfacial defects caused by imperfect energy levels between the electron transport layer and perovskite are reduced. High‐resolution transmission electron microscopy and electron energy loss spectroscopy demonstrate that a‐BaTiO3 forms entirely as a single phase, as opposed to Ba‐doped TiO2 hybrid nanoclusters or separate domains of TiO2 and BaTiO3 phases. Accordingly, inorganic perovskite solar cells based on the a‐BaTiO3 electron transport layer achieved a power conversion efficiency of 19.96%.

Space-Charging Interfacial Layer by Illumination for Efficient Sb2S3 Bulk-Heterojunction Solar Cells with High Open-Circuit Voltage

Solution-processed material systems for effective photovoltaic conversion are the key to low-cost and efficient solar cells. While antimony trisulfide (Sb2S3) is a promising photovoltaic absorber, solution-processed quality Sb2S3-based heterojunction systems for solar cells, particularly with an open-circuit voltage (Voc) higher than 0.70 V, are challenging issues. Here, a cadmium sulfide (CdS) interfacial engineering method is developed for the Sb2S3-based bulk-heterojunction (BHJ) solar cells with an efficiency of 6.14% and a Voc up to 0.76 V that is the highest one among solution-processed Sb2S3 solar cells. The prepared Sb2S3-based BHJ solar cells feature a Sb2S3 nanoparticle film interdigitated by a titania (TiO2) nanorod array with a nanostructured CdS shell as an interfacial layer on each TiO2 nanorod core. Upon understanding the interfacial interactions and band alignments in the TiO2-CdS-Sb2S3 system, the function of the CdS interfacial layer as a band-bended spatial spacer interacting strongly with both the TiO2 electron transporter and Sb2S3 absorber for increasing charge collecting efficiency is revealed; moreover, space-charging the band-bended CdS layer by illumination is found and a photogenerated interfacial dipole electric field model is proposed for understanding the high Voc subjected to the presence of the CdS interfacial layer. This work provides a conceptual guide for designing efficient inorganic heterojunction solar cells.

Intrinsic Advantage of Fused‐Ring Nonfullerene Acceptor‐Based Organic Solar Cells to Reduce Voltage Loss

The large voltage loss is a significant disadvantage of organic solar cells (OSCs) compared with inorganic and perovskite solar cells and should be reduced to further improve the power conversion efficiency of OSCs. Herein, the voltage loss in OSCs with a systematically controlled energy difference between the excited and charge transfer states is discussed. The voltage loss is compared between two types of OSCs: narrow‐bandgap donors paired with wide‐bandgap acceptors and narrow‐bandgap fused‐ring nonfullerene acceptors (NFAs) paired with wide‐bandgap donors, to elucidate whether there are any essential advantages in the latter. The first advantage of narrow‐bandgap‐NFA‐based OSCs is their higher photoluminescence quantum yield, owing to their rigid fused‐ring architecture. The second advantage is the ability to achieve efficient charge separation with a small voltage loss.