Is the Cu/Zn Disorder the Main Culprit for the Voltage Deficit in Kesterite Solar Cells?

Photovoltaic thin film solar cells based on kesterite Cu₂ZnSn(S_x,Se_1–x)₄ compounds (CZTSSe) have reached >12% sunlight‐to‐electricity conversion efficiency. This is still far from the >20% record devices known in Cu(In_1–y,Ga_y)Se₂ and CdTe parent technologies. A selection of >9% CZTSSe devices reported in the literature is examined to review the progress achieved over the past few years. These devices suffer from a low open‐circuit voltage (V_oc) never better than 60% of the V_{oc max}, which is expected from the Shockley‐Queisser radiative limit (S‐Q limit). The possible role of anionic (S/Se) distribution and of cationic (Cu/Zn) disorder on the V_oc deficit and on the ultimate photovoltaic performance of kesterite devices, are clarified here. While the S/Se anionic distribution is expected to be homogeneous for any ratio x, some grain‐to‐grain and other non‐uniformity over larger area can be found, as quantified on our CZTSSe films. Nevertheless, these anionic distributions can be considered to have a negligible impact on the V_oc deficit. On the Cu/Zn order side, even though significant bandgap changes (>10%) can be observed, a similar conclusion is brought from experimental devices and from calculations, still within the radiative S‐Q limit. The implications and future ways for improvement are discussed.     

Back Contact Engineering for Increased Performance in Kesterite Solar Cells

The thin‐film photovoltaic absorber Cu₂ZnSn(S,Se)₄ (CZTSSe) holds considerable promise for large scale conversion of sunlight into electricity. CZTSSe is composed of Earth‐abundant elements that exhibit low‐toxicities, but improvements in device efficiency have been hampered by difficulties in increasing open circuit voltages (V_OC) due, at least in part, to disorder induced band tailing. We present a method to increase V_OC through direct modification of the back contact; our approach involves the separation of fully functioning devices from their Mo/glass substrate to reveal the back CZTSSe surface. Formation of a new back contact consisting of a thermally deposited high work function material (MoO₃), together with a higly reflective (Au) capping layer, creates an electrostatic field that drives electrons to the front p‐n junction and leads to a decrease in electron‐hole recombination. Model simulations indicating an increase in V_OC with decreasing absorber thickness are borne out by experiments with devices of varying thicknesses (0.7–2.0 μm). We report V_OC increases of up to 49 mV for a 1 μm thick absorber, with even greater increases up to 61 mV when the back CZTSSe surface is etched with bromine‐methanol.     

Record Open‐Circuit Voltage Wide‐Bandgap Perovskite Solar Cells Utilizing 2D/3D Perovskite Heterostructure

In this work, the authors realize stable and highly efficient wide‐bandgap perovskite solar cells that promise high power conversion efficiencies (PCE) and are likely to play a key role in next generation multi‐junction photovoltaics (PV). This work reports on wide‐bandgap (≈1.72 eV) perovskite solar cells exhibiting stable PCEs of up to 19.4% and a remarkably high open‐circuit voltage (V_OC) of 1.31 V. The V_OC‐to‐bandgap ratio is the highest reported for wide‐bandgap organic?inorganic hybrid perovskite solar cells and the V_OC also exceeds 90% of the theoretical maximum, defined by the Shockley–Queisser limit. This advance is based on creating a hybrid 2D/3D perovskite heterostructure. By spin coating n‐butylammonium bromide on the double‐cation perovskite absorber layer, a thin 2D Ruddlesden–Popper perovskite layer of intermediate phases is formed, which mitigates nonradiative recombination in the perovskite absorber layer. As a result, V_OC is enhanced by 80 mV.     

Absence of Charge Transfer State Enables Very Low VOC Losses in SWCNT:Fullerene Solar Cells

Current state‐of‐the‐art organic solar cells (OSCs) still suffer from high losses of open‐circuit voltage (V_OC). Conventional polymer:fullerene solar cells usually exhibit bandgap to V_OC losses greater than 0.8 V. Here a detailed investigation of V_OC is presented for solution‐processed OSCs based on (6,5) single‐walled carbon nanotube (SWCNT): [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester active layers. Considering the very small optical bandgap of only 1.22 eV of (6,5) SWCNTs, a high V_OC of 0.59 V leading to a low E_gap/q ? V_OC = 0.63 V loss is observed. The low voltage losses are partly due to the lack of a measurable charge transfer state and partly due to the narrow absorption edge of SWCNTs. Consequently, V_OC losses attributed to a broadening of the band edge are very small, resulting in V_OC,SQ ? V_OC,rad = 0.12 V. Interestingly, this loss is mainly caused by minor amounts of SWCNTs with smaller bandgaps as well as (6,5) SWCNT trions, all of which are experimentally well resolved employing Fourier transform photocurrent spectroscopy. In addition, the low losses due to band edge broadening, a very low voltage loss are also found due to nonradiative recombination, ΔV_OC,nonrad = 0.26 V, which is exceptional for fullerene‐based OSCs.     

Hybrid Perovskite‐Organic Flexible Tandem Solar Cell Enabling Highly Efficient Electrocatalysis Overall Water Splitting

Perovskite‐organic tandem solar cells are attracting more attention due to their potential for highly efficient and flexible photovoltaic device. In this work, efficient perovskite‐organic monolithic tandem solar cells integrating the wide bandgap perovskite (1.74 eV) and low bandgap organic active PBDB‐T:SN6IC‐4F (1.30 eV) layer, which serve as the top and bottom subcell, respectively, are developed. The resulting perovskite‐organic tandem solar cells with passivated wide‐bandgap perovskite show a remarkable power conversion efficiency (PCE) of 15.13%, with an open‐circuit voltage (V_oc) of 1.85 V, a short‐circuit photocurrent (J_sc) of 11.52 mA cm^?2, and a fill factor (FF) of 70.98%. Thanks to the advantages of low temperature fabrication processes and the flexibility properties of the device, a flexible tandem solar cell which obtain a PCE of 13.61%, with V_oc of 1.80 V, J_sc of 11.07 mA cm^?2, and FF of 68.31% is fabricated. Moreover, to demonstrate the achieved high V_oc in the tandem solar cells for potential applications, a photovoltaic (PV)‐driven electrolysis system combing the tandem solar cell and water splitting electrocatalysis is assembled. The integrated device demonstrates a solar‐to‐hydrogen efficiency of 12.30% and 11.21% for rigid, and flexible perovskite‐organic tandem solar cell based PV‐driven electrolysis systems, respectively.     

15% Efficiency Tandem Organic Solar Cell Based on a Novel Highly Efficient Wide‐Bandgap Nonfullerene Acceptor with Low Energy Loss

A tandem organic solar cell (OSC) is a valid structure to widen the photon response range and suppress the transmission loss and thermalization loss. In the past few years, the development of low‐bandgap materials with broad absorption in long‐wavelength region for back subcells has attracted considerable attention. However, wide‐bandgap materials for front cells that have both high short‐circuit current density (J_SC) and open‐circuit voltage (V_OC) are scarce. In this work, a new fluorine‐substituted wide‐bandgap small molecule nonfullerene acceptor TfIF‐4FIC is reported, which has an optical bandgap of 1.61 eV. When PBDB‐T‐2F is selected as the donor, the device offers an extremely high V_OC of 0.98 V, a high J_SC of 17.6 mA cm^?2, and a power conversion efficiency of 13.1%. This is the best performing acceptor with such a wide bandgap. More importantly, the energy loss in this combination is 0.63 eV. These properties ensure that PBDB‐T‐2F:TfIF‐4FIC is an ideal candidate for the fabrication of tandem OSCs. When PBDB‐T‐2F:TfIF‐4FIC and PTB7‐Th:PCDTBT:IEICO‐4F are used as the front cell and the back cell to construct tandem solar cells, a PCE of 15% is obtained, which is one of best results reported to date in the field of organic solar cells.     

Thin‐Film Solar Cells with InP Absorber Layers Directly Grown on Nonepitaxial Metal Substrates

The design and performance of solar cells based on InP grown by the nonepitaxial thin‐film vapor–liquid–solid (TF‐VLS) growth technique is investigated. The cell structure consists of a Mo back contact, p‐InP absorber layer, n‐TiO₂ electron selective contact, and indium tin oxide transparent top electrode. An ex situ p‐doping process for TF‐VLS grown InP is introduced. Properties of the cells such as optoelectronic uniformity and electrical behavior of grain boundaries are examined. The power conversion efficiency of first generation cells reaches 12.1% under simulated 1 sun illumination with open‐circuit voltage (V_OC) of 692 mV, short‐circuit current (J_SC) of 26.9 mA cm^?2, and fill factor (FF) of 65%. The FF of the cell is limited by the series resistances in the device, including the top contact, which can be mitigated in the future through device optimization. The highest measured V_OC under 1 sun is 692 mV, which approaches the optically implied V_OC of ≈795 mV extracted from the luminescence yield of p‐InP.     

Suppressing Interfacial Dipoles to Minimize Open‐Circuit Voltage Loss in Quantum Dot Photovoltaics

Quantum‐dot (QD) photovoltaics (PVs) offer promise as energy‐conversion devices; however, their open‐circuit‐voltage (V_OC) deficit is excessively large. Previous work has identified factors related to the QD active layer that contribute to V_OC loss, including sub‐bandgap trap states and polydispersity in QD films. This work focuses instead on layer interfaces, and reveals a critical source of V_OC loss: electron leakage at the QD/hole‐transport layer (HTL) interface. Although large‐bandgap organic materials in HTL are potentially suited to minimizing leakage current, dipoles that form at an organic/metal interface impede control over optimal band alignments. To overcome the challenge, a bilayer HTL configuration, which consists of semiconducting alpha‐sexithiophene (α‐6T) and metallic poly(3,4‐ethylenedioxythiphene) polystyrene sulfonate (PEDOT:PSS), is introduced. The introduction of the PEDOT:PSS layer between α‐6T and Au electrode suppresses the formation of undesired interfacial dipoles and a Schottky barrier for holes, and the bilayer HTL provides a high electron barrier of 1.35 eV. Using bilayer HTLs enhances the V_OC by 74 mV without compromising the J_SC compared to conventional MoO₃ control devices, leading to a best power conversion efficiency of 9.2% (>40% improvement relative to relevant controls). Wider applicability of the bilayer strategy is demonstrated by a similar structure based on shallow lowest‐unoccupied‐molecular‐orbital (LUMO) levels.     

Terthieno[3,2‐b]Thiophene (6T) Based Low Bandgap Fused‐Ring Electron Acceptor for Highly Efficient Solar Cells with a High Short‐Circuit Current Density and Low Open‐Circuit Voltage Loss

A terthieno[3,2‐b]thiophene ( 6T ) based fused‐ring low bandgap electron acceptor, 6TIC , is designed and synthesized for highly efficient nonfullerene solar cells. The chemical, optical, and physical properties, device characteristics, and film morphology of 6TIC are intensively studied. 6TIC shows a narrow bandgap with band edge reaching 905 nm due to the electron‐rich π‐conjugated 6T core and reduced resonance stabilization energy. The rigid, π‐conjugated 6T also offers lower reorganization energy to facilitate very low V_OC loss in the 6TIC system. The analysis of film morphology shows that PTB7‐Th and 6TIC can form crystalline domains and a bicontinuous network. These domains are enlarged when thermal annealing is applied. Consequently, the device based on PTB7‐Th : 6TIC exhibits a high power conversion efficiency (PCE) of 11.07% with a high J_SC > 20 mA cm^?2 and a high V_OC of 0.83 V with a relatively low V_OC loss (≈0.55 V). Moreover, a semitransparent solar cell based on PTB7‐Th : 6TIC exhibits a relatively high PCE (7.62%). The device can have combined high PCE and high J_SC is quite rare for organic solar cells.     

All‐Polymer Solar Cells with over 12% Efficiency and a Small Voltage Loss Enabled by a Polymer Acceptor Based on an Extended Fused Ring Core

Although the field of all‐polymer solar cells (all‐PSCs) has seen rapid progress in device efficiencies during the past few years, there are limited choices of polymer acceptors that exhibit strong absorption in the near‐IR region and achieve high open‐circuit voltage (V_OC) at the same time. In this paper, an all‐PSC device is demonstrated with a 12.06% efficiency based on a new polymer acceptor (named PT‐IDTTIC) that exhibits strong absorption (maximum absorption coefficient: 2.41 × 10⁵ cm^?1) and a narrow optical bandgap (1.49 eV). Compared to previously reported polymer acceptors such as those based on the indacenodithiophene (IDT) core, the indacenodithienothiophene (IDTT) core has further extended fused ring, providing the polymer with extended absorption into the near‐IR region and also increases the electron mobility of the polymer. By blending PT‐IDTTIC with the donor polymer, PM6, a high‐efficiency all‐PSC is achieved with a small voltage loss of 0.52 V, without sacrificing J_SC and FF, which demonstrates the great potential of high‐performance all‐PSCs.     

Improved Open‐ Circuit Voltage in ZnO–PbSe Quantum Dot Solar Cells by Understanding and Reducing Losses Arising from the ZnO Conduction Band Tail

Colloidal quantum dot solar cells (CQDSCs) are attracting growing attention owing to significant improvements in efficiency. However, even the best depleted‐heterojunction CQDSCs currently display open‐circuit voltages (V_OCs) at least 0.5 V below the voltage corresponding to the bandgap. We find that the tail of states in the conduction band of the metal oxide layer can limit the achievable device efficiency. By continuously tuning the zinc oxide conduction band position via magnesium doping, we probe this critical loss pathway in ZnO–PbSe CQDSCs and optimize the energetic position of the tail of states, thereby increasing both the V_OC (from 408 mV to 608 mV) and the device efficiency.     

Open‐Circuit Voltage in Organic Solar Cells: The Impacts of Donor Semicrystallinity and Coexistence of Multiple Interfacial Charge‐Transfer Bands

In organic solar cells (OSCs), the energy of the charge‐transfer (CT) complexes at the donor–acceptor interface, E _CT, determines the maximum open‐circuit voltage (V _OC). The coexistence of phases with different degrees of order in the donor or the acceptor, as in blends of semi‐crystalline donors and fullerenes in bulk heterojunction layers, influences the distribution of CT states and the V _OC enormously. Yet, the question of how structural heterogeneities alter CT states and the V _OC is seldom addressed systematically. In this work, we combine experimental measurements of vacuum‐deposited rubrene/C₆₀ bilayer OSCs, with varying microstructure and texture, with density functional theory calculations to determine how relative molecular orientations and extents of structural order influence E _CT and V _OC. We find that varying the microstructure of rubrene gives rise to CT bands with varying energies. The CT band that originates from crystalline rubrene lies up to ≈0.4 eV lower in energy compared to the one that arises from amorphous rubrene. These low‐lying CT states contribute strongly to V _OC losses and result mainly from hole delocalization in aggregated rubrene. This work points to the importance of realizing interfacial structural control that prevents the formation of low E _CT configurations and maximizes V _OC.     

Understanding Open‐Circuit Voltage Loss through the Density of States in Organic Bulk Heterojunction Solar Cells

The field of organic photovoltaics has recently produced highly efficient single‐junction cells with power conversion efficiency >10%, yet the open‐circuit voltage (V_OC) remains relatively low in many high performing systems. An accurate picture of the density of states (DOS) in working solar cells is crucial to understanding the sources of voltage loss, but remains difficult to obtain experimentally. Here, the tail of the DOS is characterized in a number of small molecule bulk heterojunction solar cells from the charge density dependence of V_OC, and is directly compared to the disorder present within donor and acceptor components as measured by Kelvin probe. Using these DOS distributions, the total energy loss relative to the charge transfer state energy (E_CT)—ranging from ≈0.5 to 0.7 eV—is divided into contributions from energetic disorder and from charge recombination, and the extent to which these factors limit the V_OC is assessed.     

Dithienogermole‐Containing Small‐Molecule Solar Cells with 7.3% Efficiency: In‐Depth Study on the Effects of Heteroatom Substitution of Si with Ge

Two small molecule donor materials (DTGe(FBTTh₂)₂ and DTGe(FBTBFu)₂) incorporating the dithienogermole (DTGe) moiety with fluorobenzothiadiazole (FBT) and bithiophene (Th₂) or benzofuran (BFu) end‐capping groups are synthesized and their properties as donor materials in small molecule bulk heterojunction type (BHJ) solar cells are investigated. The DTGe(FBTTh₂)₂ with Th₂ end groups shows outstanding solar cell characteristics with efficiencies up to 6.4% using a standard BHJ architecture and 7.3% using a ZnO optical spacer, while the BFu end‐capped DTGe(FBTBFu)₂ has slightly wider band gaps and yields slightly higher open circuit voltage (V_OC) at the expense of short circuit current (J_SC) and fill factor (FF). In this study, the DTGe‐based molecules are systematically compared to the dithienosilole (DTSi)‐based analogues, which are currently among the highest power conversion efficiency (PCE) small molecule solar cell donor materials known. The J_SC produced by the DTGe molecule is found to be similar to, or slightly higher than the Si analogue, despite similar absorption characteristics, however, the PCE is similar to the Si analogues due to small decreases in V_OC and FF. This report marks the first small molecule BHJ based on a Ge‐containing heterocycle with PCE over 7%.     

Reducing Voltage Losses in Cascade Organic Solar Cells while Maintaining High External Quantum Efficiencies

High photon energy losses limit the open‐circuit voltage (V_OC) and power conversion efficiency of organic solar cells (OSCs). In this work, an optimization route is presented which increases the V_OC by reducing the interfacial area between donor (D) and acceptor (A). This optimization route concerns a cascade device architecture in which the introduction of discontinuous interlayers between alpha‐sexithiophene (α‐6T) (D) and chloroboron subnaphthalocyanine (SubNc) (A) increases the V_OC of an α‐6T/SubNc/SubPc fullerene‐free cascade OSC from 0.98 V to 1.16 V. This increase of 0.18 V is attributed solely to the suppression of nonradiative recombination at the D–A interface. By accurately measuring the optical gap (E_opt) and the energy of the charge‐transfer state (E_CT) of the studied OSC, a detailed analysis of the overall voltage losses is performed. E_opt – qV_OC losses of 0.58 eV, which are among the lowest observed for OSCs, are obtained. Most importantly, for the V_OC‐optimized devices, the low‐energy (700 nm) external quantum efficiency (EQE) peak remains high at 79%, despite a minimal driving force for charge separation of less than 10 meV. This work shows that low‐voltage losses can be combined with a high EQE in organic photovoltaic devices.     

Influence of Fullerene Acceptor on the Performance,Microstructure, and Photophysics of Low Bandgap Polymer Solar Cells

The morphology, photophysics, and device performance of solar cells based on the low bandgap polymer poly[[2,6′‐4,8‐di(5‐ethylhexylthienyl)benzo[1,2‐b;3,3‐b]dithiophene]3‐fluoro‐2[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl (PBDTTT‐EFT) (also known as PTB7‐Th) blended with different fullerene acceptors: Phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM), phenyl‐C₇₁ ‐butyric acid methyl ester (PC₇₁BM), or indene‐C₆₀ bisadduct (ICBA) are correlated. Compared to PC₇₁ BM‐based cells – which achieve a power conversion efficiency (PCE) of 9.4% – cells using ICBA achieve a higher open‐circuit voltage (V_OC) of 1.0 V albeit with a lower PCE of 7.1%. To understand the origin of this lower PCE, the morphology and photophysics have been thoroughly characterized. Hard and soft X‐ray scattering measurements reveal that the PBDTTT‐EFT:ICBA blend has a lower crystallinity, lower domain purity, and smaller domain size compared to the PBDTTT‐EFT:PC₇₁BM blend. Incomplete photoluminescence quenching is also found in the ICBA blend with transient absorption measurements showing faster recombination dynamics at short timescales. Transient photovoltage measurements highlight further differences in recombination at longer timeframes due to the more intermixed morphology of the ICBA blend. Interestingly, a mild thermal treatment improves the performance of PBDTTT‐EFT:ICBA cells which is exploited in the fabrication of a homo PBDTTT‐EFT:ICBA tandem solar cell with PCE of 9.0% and V_OC of 1.93 V.     

The Introduction of Fluorine and Sulfur Atoms into Benzotriazole‐Based p‐Type Polymers to Match with a Benzotriazole‐Containing n‐Type Small Molecule: “The Same‐Acceptor‐Strategy” to Realize High Open‐Circuit Voltage

“The Same‐Acceptor‐Strategy” (SAS) adopts benzotriazole (BTA)‐based p‐type polymers paired with a new BTA based non‐fullerene acceptor BTA13 to minimize the trade‐off between the open‐circuit voltage (V_OC) and short circuit current (J_SC). The fluorination and sulfuration are introduced to lower the highest occupied molecular orbitals (HOMO) of the polymers. The fluorinated polymer of J52‐F shows the higher power conversion efficiency (PCE) of 8.36% than the analog polymer of J52, benefited from a good balance between an improved V_OC of 1.18 V and a J_SC of 11.55 mA cm^?2. Further adding alkylthio groups on J52‐F, the resulted polymer, J52‐FS, exhibits the highest V_OC of 1.24 V with a decreased energy loss of 0.48 eV, compared with 0.67 eV for J52 and 0.54 eV for J52‐F. However, J52‐FS shows an inferior PCE (3.84%) with a lower J_SC of 6.74 mA cm^?2, because the small ΔE_HOMO between J52‐FS and BTA13 (0.02 eV) gives rise to the inefficient hole transfer and high charge recombination, as well as low carrier mobilities. The results of this study clearly demonstrate that the introduction of different atoms in p‐type polymers is effective to improve the SAS and realize the high (V_OC) and PCE.     

Achieving 17.4% Efficiency of Ternary Organic Photovoltaics with Two Well‐Compatible Nonfullerene Acceptors for Minimizing Energy Loss

A power conversion efficiency (PCE) of 16.2% is achieved in PM6:BTP‐4F‐12 based organic photovoltaics (OPVs). On the basis of efficient binary OPVs, a series of ternary OPVs are constructed by incorporating MeIC as the third component. The open circuit voltages (V_OCs) of ternary OPVs can be gradually increased along with the incorporation of MeIC, suggesting the formation of an alloy state between BTP‐4F‐12 and MeIC with good compatibility. The energy loss (E_loss) of ternary OPVs can be decreased compared with that of two binary OPVs, contributing to the V_OC improvement of ternary OPVs. The short circuit current density (J_SC) and fill factor (FF) of ternary OPVs can also be simultaneously enhanced with MeIC content up to 10 wt% in acceptors, leading to 17.4% PCE of the optimized ternary OPVs. The J_SC and FF improvement of ternary OPVs is thought to result from the optimized ternary active layers with more efficient photon harvesting, exciton dissociation and charge transport. The 17.4% PCE and 79.2% FF is among the top values of ternary OPVs. This work indicates that a ternary strategy is an emerging method to simultaneously minimize E_loss and optimize photon harvesting as well as improve the morphology of active layers for realizing performance improvement for OPVs.     

On the Relation between the Open‐Circuit Voltage and Quasi‐Fermi Level Splitting in Efficient Perovskite Solar Cells

Today's perovskite solar cells (PSCs) are limited mainly by their open‐circuit voltage (V_OC) due to nonradiative recombination. Therefore, a comprehensive understanding of the relevant recombination pathways is needed. Here, intensity‐dependent measurements of the quasi‐Fermi level splitting (QFLS) and of the V_OC on the very same devices, including pin‐type PSCs with efficiencies above 20%, are performed. It is found that the QFLS in the perovskite lies significantly below its radiative limit for all intensities but also that the V_OC is generally lower than the QFLS, violating one main assumption of the Shockley‐Queisser theory. This has far‐reaching implications for the applicability of some well‐established techniques, which use the V_OC as a measure of the carrier densities in the absorber. By performing drift‐diffusion simulations, the intensity dependence of the QFLS, the QFLS‐V_OC offset and the ideality factor are consistently explained by trap‐assisted recombination and energetic misalignment at the interfaces. Additionally, it is found that the saturation of the V_OC at high intensities is caused by insufficient contact selectivity while heating effects are of minor importance. It is concluded that the analysis of the V_OC does not provide reliable conclusions of the recombination pathways and that the knowledge of the QFLS‐V_OC relation is of great importance.     

Bandgap Narrowing in Non‐Fullerene Acceptors: Single Atom Substitution Leads to High Optoelectronic Response Beyond 1000 nm

Two narrow bandgap non‐fullerene acceptors (NBG‐NFAs), namely, COTIC‐4F and SiOTIC‐4F, are designed and synthesized for the fabrication of efficient near‐infrared organic solar cells (OSCs). The chemical structures of the NBG‐NFAs contain a D′‐D‐D′ electron‐rich internal core based on a cyclopentadithiophene (or dithienosilole) (D) and alkoxythienyl (D′) core, end‐capped with the highly electron‐deficient unit 2‐(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene)malononitrile (A), ultimately providing a A‐D′‐D‐D′‐A molecular configuration that enhances the intramolecular charge transfer characteristics of the excited states. One can thereby reduce the optical bandgap (E_g^opt) to as low as ≈1.10 eV, one of the smallest values for NFAs reported to date. In bulk‐heterojunction (BHJ) OSCs, NBG‐NFA blends with the polymer donor PTB7‐Th yield power conversion efficiencies (PCE) of up to 9.0%, which is particularly high when compared against a range of NBG BHJ blends. Most significantly, it is found that, despite the small energy loss (E_g^opt ? eV_OC) of 0.52 eV, the PTB7‐Th/NBG‐NFA bulk heterojunction blends can yield short‐circuit current densities of up to 22.8 mA cm^?2, suggesting that the design and application of NBG‐NFA materials have substantial potential to further improve the PCE of OSCs.