Efficient Organic Solar Cells with Extremely High Open‐Circuit Voltages and Low Voltage Losses by Suppressing Nonradiative Recombination Losses

One of the most important factors that limits the efficiencies of bulk‐heterojunction organic solar cells (OSCs) is the modest open‐circuit voltage (V_oc) due to their large voltage loss (V_loss) caused by significant nonradiative recombination loss. To boost the performance of OSCs toward their theoretical limit, developing high‐performance donor: acceptor systems featuring low V_loss with suppressed nonradiative recombination losses (<0.30 V) is desired. Herein, high performance OSCs based on a polymer donor benzodithiophene‐difluorobenzoxadiazole‐2‐decyltetradecyl (BDT‐ffBX‐DT) and perylenediimide‐based acceptors (PDI dimer with spirofluorene linker (SFPDI), PDI4, and PDI6) are reported which offer a high power conversion efficiency (PCE) of 7.5%, 56% external quantum efficiency associated with very high V_oc (>1.10 V) and low V_loss (<0.60 V). A high V_oc up to 1.23 V is achieved, which is among the highest values reported for OSCs with a PCE beyond 6%, to date. These attractive results are benefit from the suppressed nonradiative recombination voltage loss, which is as low as 0.20 V. This value is the lowest value for OSCs so far and is comparable to high performance crystalline silicon and perovskite solar cells. These results show that OSCs have the potential to achieve comparable V_oc and voltage loss as inorganic photovoltaic technologies.     

Modulation of End Groups for Low‐Bandgap Nonfullerene Acceptors Enabling High‐Performance Organic Solar Cells

The field of nonfullerene organic solar cells (OSCs) has seen an impressive progress, largely due to advances in high‐performance small molecule acceptors (SMAs). As a large portion of the solar energy is located in the near‐infrared region, it is important to develop ultralow‐bandgap SMAs that have extended absorption in the spectral range of 800–1000 nm to maximize light absorption and efficiencies. In this work, three low‐bandgap SMAs, namely, IXIC, IXIC‐2Cl, and IXIC‐4Cl, are designed and synthesized with same fused terthieno[3,2‐b]thiophene donor unit and different end groups (EGs). The three SMAs all have low optical bandgap (E_g) of 1.35, 1.30, and 1.25 eV, respectively. The chlorination on EGs can lower the energy level and broaden absorption range of the SMAs. As a result, the V_oc of the devices is reduced but the J_sc is significantly increased. In addition, the addition of chlorine atoms can enhance π–π stacking and crystallinity of the SMAs, which result in high fill factors. Overall, the optimum EGs are monochlorine‐substituted IC and OSCs based on PBDB‐T:IXIC‐2Cl that can achieve remarkable power conversion efficiencies (PCEs) of 12.2%, which is one of the highest PCEs for nonfullerene organic solar cells based on low‐bandgap SMAs.     

Reduced Energy Loss Enabled by a Chlorinated Thiophene‐Fused Ending‐Group Small Molecular Acceptor for Efficient Nonfullerene Organic Solar Cells with 13.6% Efficiency

Generally, highly efficient organic solar cells require both a high open‐circuit voltage (V_OC) and a high short‐circuit current density (J_SC). Reducing the energy loss (E_loss) is an effective way to achieve a high V_OC without compromising the photocurrent, which is ideal for enhancing the power conversion efficiencies (PCEs). Herein, a new chlorinated nonfullerene acceptor (ITC‐2Cl) with chlorinated thiophene‐fused end groups is developed. In comparison with the unchlorinated counterpart (ITCPTC), the introduction of Cl improves not only the electronic properties by redshifting the absorption spectra and deepening the lowest unoccupied molecular orbital energy levels, but also the molecular packing and thus thin‐film morphology. The PM6:ITC‐2Cl‐based device yields a significantly higher PCE (13.6%) with a lower E_loss (0.67 eV) than the ITCPTC‐based device (PCE of 12.3% with E_loss of 0.70 eV). More importantly, compared to the archetypal nonfullerene acceptors such as IT‐4F (PCE of 12.9% with E_loss of 0.73 eV) and IT‐4Cl (PCE of 12.7% with E_loss of 0.76 eV), the ITC‐2Cl‐based device shows a higher PCE and a lower E_loss. These results demonstrate that the chlorinated thiophene‐fused end group is a promising candidate for a high‐performance nonfullerene acceptors with low energy loss.     

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.     

Reduced Nonradiative Energy Loss Caused by Aggregation of Nonfullerene Acceptor in Organic Solar Cells

Reducing energy loss (E_loss) is of critical importance to improving the photovoltaic performance of organic solar cells (OSCs). Although nonradiative recombination ( $E_{\mathrm{loss}}^{\mathrm{nonrad}}$) is investigated in quite a few works, the method for modulating $E_{\mathrm{loss}}^{\mathrm{nonrad}}$ is seldom reported. Here, a new method of depressing E_loss is reported for nonfullerene OSCs. In addition to ternary‐blend bulk heterojunction (BHJ) solar cells, it is proved that a small molecular material (NRM‐1) can be selectively dispersed into the acceptor phase in the PBDB‐T:IT‐4F‐based OSC, resulting in lower $E_{\mathrm{loss}}^{\mathrm{rad}}$ and $E_{\mathrm{loss}}^{\mathrm{nonrad}}$, and hence a significant improvement in the open‐circuit voltage (V_OC); under an optimal feed ratio of NRM‐1, an enhanced power conversion efficiency can also be gained. Moreover, the role of NRM‐1 in the method is illustrated and its applicability for several other representative OSCs is validated. This work paves a new pathway to reduce the E_loss for nonfullerene OSCs.     

An Efficient Solution‐Processed Intermediate Layer for Facilitating Fabrication of Organic Multi‐Junction Solar Cells

Photovoltaic tandem technology has the potential to boost the power conversion efficiency of organic photovoltaic devices. Here, a reliable and efficient fully solution‐processed intermediate layer (IML) consisting of ZnO and neutralized poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is demonstrated for series‐connected multi‐junction organic solar cells (OSCs). Drying at 80 °C in air is sufficient for this solution‐processed IML to obtain excellent functionality and reliability, which allow the use of most of high performance donor materials in the tandem structure. An open circuit voltage (V_oc) of 0.56 V is obtained for single‐junction OSCs based on a low band‐gap polymer, while multi‐junction OSCs based on the same absorber material deliver promising fill factor values along with fully additive V_oc as the number of junctions increase. Optical and electrical simulations, which are reliable and promising guidelines for the design and investigation of multi‐junction OSCs, are discussed. The outcome of optical and electrical simulations is in excellent agreement with the experimental data, indicating the outstanding efficiency and functionality of this solution‐processed IML. The demonstration of this efficient, solution‐processed IML represents a convenient way for facilitating fabrication of multi‐junction OSCs to achieve high power conversion efficiency.     

Vacuum‐Assisted Growth of Low‐Bandgap Thin Films (FA0.8MA0.2Sn0.5Pb0.5I3) for All‐Perovskite Tandem Solar Cells

All‐perovskite multijunction photovoltaics, combining a wide‐bandgap (WBG) perovskite top solar cell (E_G ≈1.6–1.8 eV) with a low‐bandgap (LBG) perovskite bottom solar cell (E_G < 1.3 eV), promise power conversion efficiencies (PCEs) >33%. While the research on WBG perovskite solar cells has advanced rapidly over the past decade, LBG perovskite solar cells lack PCE as well as stability. In this work, vacuum‐assisted growth control (VAGC) of solution‐processed LBG perovskite thin films based on mixed Sn–Pb perovskite compositions is reported. The reported perovskite thin films processed by VAGC exhibit large columnar crystals. Compared to the well‐established processing of LBG perovskites via antisolvent deposition, the VAGC approach results in a significantly enhanced charge‐carrier lifetime. The improved optoelectronic characteristics enable high‐performance LBG perovskite solar cells (1.27 eV) with PCEs up to 18.2% as well as very efficient four‐terminal all‐perovskite tandem solar cells with PCEs up to 23%. Moreover, VAGC leads to promising reproducibility and potential in the fabrication of larger active‐area solar cells up to 1 cm².     

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.     

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.     

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.     

Overcoming the “Light‐Soaking” Issue in Inverted Organic Solar Cells by the Use of Al:ZnO Electron Extraction Layers

A common phenomenon of organic solar cells (OSCs) incorporating metal‐oxide electron extraction layers is the requirement to expose the devices to UV light in order to improve device characteristics – known as the so‐called “light‐soaking” issue. This behaviour appears to be of general validity for various metal‐oxide layers, various organic donor/acceptor systems, and regardless if single junction devices or multi stacked cells are considered. The requirement of UV exposure of OSCs may impose severe problems if substrates with limited UV transmission, UV blocking filters or UV to VIS down‐conversion concepts are applied. In this paper, we will demonstrate that this issue can be overcome by the use of Al doped ZnO (AZO) as electron extraction interlayer. In contrast to devices based on TiO_x and ZnO, the AZO devices show well‐behaved solar cell characteristics with a high fill factor (FF) and power conversion efficiency (PCE) even without the UV spectral components of the AM1.5 solar spectrum. As opposed to previous claims, our results indicate that the origin of s‐shaped characteristics of the OSCs is the metal‐oxide/organic interface. The electronic structures of the TiO_x/fullerene and AZO/fullerene interfaces are studied by photoelectron spectroscopy, revealing an electron extraction barrier for the TiO_x/fullerene case and facilitated electron extraction for AZO/fullerene. These results are of general relevance for organic solar cells based on various donor acceptor active systems.     

Benzo[1,2‐b:4,5‐b′]Dithiophene–6,7‐Difluoroquinoxaline Small Molecule Donors with >8% BHJ Solar Cell Efficiency

Solution‐processable small molecule (SM) donors are promising alternatives to their polymer counterparts in bulk‐heterojunction (BHJ) solar cells. While SM donors with favorable spectral absorption, self‐assembly patterns, optimum thin‐film morphologies, and high carrier mobilities in optimized donor–acceptor blends are required to further BHJ device efficiencies, material structure governs each one of those attributes. As a result, the rational design of SM donors with gradually improved BHJ solar cell efficiencies must concurrently address: (i) bandgap tuning and optimization of spectral absorption (inherent to the SM main chain) and (ii) pendant‐group substitution promoting structural order and mediating morphological effects. In this paper, the rational pendant‐group substitution in benzo[1,2‐b:4,5‐b′]dithiophene–6,7‐difluoroquinoxaline SMs is shown to be an effective approach to narrowing the optical gap (E_opt) of the SM donors ( SM1 and SM2 ), without altering their propensity to order and form favorable thin‐film BHJ morphologies with PC₇₁BM. Systematic device examinations show that power conversion efficiencies >8% and open‐circuit voltages (V_OC) nearing 1 V can be achieved with the narrow‐gap SM donor analog ( SM2 , E_opt = 1.6 eV) and that charge transport in optimized BHJ solar cells proceeds with minimal, nearly trap‐free recombination. Detailed device simulations, light intensity dependence, and transient photocurrent analyses emphasize how carrier recombination impacts BHJ device performance upon optimization of active layer thickness and morphology.     

Thieno[3,4‐c]Pyrrole‐4,6‐Dione‐Based Polymer Acceptors for High Open‐Circuit Voltage All‐Polymer Solar Cells

While polymer acceptors are promising fullerene alternatives in the fabrication of efficient bulk heterojunction (BHJ) solar cells, the range of efficient material systems relevant to the “all‐polymer” BHJ concept remains narrow, and currently limits the perspectives to meet the 10% efficiency threshold in all‐polymer solar cells. This report examines two polymer acceptor analogs composed of thieno[3,4‐c ]pyrrole‐4,6‐dione (TPD) and 3,4‐difluorothiophene ([2F]T) motifs, and their BHJ solar cell performance pattern with a low‐bandgap polymer donor commonly used with fullerenes (PBDT‐TS1; taken as a model system). In this material set, the introduction of a third electron‐deficient motif, namely 2,1,3‐benzothiadiazole (BT), is shown to (i) significantly narrow the optical gap (E _opt) of the corresponding polymer (by ≈0.2 eV) and (ii) improve the electron mobility of the polymer by over two orders of magnitude in BHJ solar cells. In turn, the narrow‐gap P2TPDBT[2F]T analog (E _opt = 1.7 eV) used as fullerene alternative yields high open‐circuit voltages (V _OC) of ≈1.0 V, notable short‐circuit current values (J _SC) of ≈11.0 mA cm⁻², and power conversion efficiencies (PCEs) nearing 5% in all‐polymer BHJ solar cells. P2TPDBT[2F]T paves the way to a new, promising class of polymer acceptor candidates.     

Harmonious Compatibility Dominates Influence of Side‐Chain Engineering on Morphology and Performance of Ternary Solar Cells

A growing number of recent studies have demonstrated the substantial impact of the alkyl side chains on the device performance of organic semiconductors. However, detailed investigation of the effect of side‐chain engineering on the blend morphology and performance of ternary organic solar cells (OSCs) has not yet been undertaken. In this study, the performance of ternary OSCs is investigated in a given poly(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b;4,5‐b′]dithiophene‐2,6‐diyl‐alt‐(4‐(2‐ethylhexyl)‐3‐fluorothieno[3,4‐b]thiophene‐)‐2‐carboxylate‐2‐6‐diyl)):[6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PTB7‐Th:PC₇₁BM) host set by introducing various small molecule donors (SMDs) with different terminal side‐chain lengths. As expected, the performance of binary OSCs with SMDs depends greatly on the side‐chain length. In contrast, it is observed that all SMD‐based ternary OSCs exhibit almost identical and high power‐conversion efficiencies of 12.0–12.2%. This minor performance variation is attributed to good molecular compatibility between the two donor components, as evidenced by in‐depth electrical and morphological investigations. These results highlight that the alloy‐like structure formed due to the high compatibility of the donor molecules has a more significant effect on the overall performance than the side‐chain length, offering a new guideline for pairing donor components for achieving high‐performance ternary OSCs.     

Significant Effect of Fluorination on Simultaneously Improving Work Function and Transparency of Anode Interlayer for Organic Solar Cells

Since the highest occupied molecular orbital (HOMO) level of donors in organic solar cells (OSCs) is being constantly downshifted for achieving high open‐circuit voltage (V_oc), a further enhancement of the anode work function (WF) is required. Herein, an effective approach of fluorination is demonstrated to simultaneously improve the WF and transparency for anode interlayer (AIL) material. By fluorination, in combination with the dialysis treatment in LiCl solution, the WF of PCP‐2F‐Li could be significantly enhanced from 4.86 to 5.0 eV, as compared to PCP‐Na. Meanwhile, the transparency of the polymer is also improved. As a result, PCP‐2F‐Li can be used to modify efficient active layers consisting of polymer donors with deep HOMO levels, such as PBDB‐T‐2F:IT‐4F, and an outstanding power conversion efficiency (PCE) of 12.7% is achieved in the corresponding device with a high V_oc of 0.84 V. This result represents the highest efficiency for the OSCs using a solution‐processed pH‐neutral AIL, which is beneficial to the low‐cost fabrication of high‐performance OSCs with improved stability. More importantly, PCP‐2F‐Li could be processed by blade coating for making large‐area device of 1 cm², and a PCE of 10.6% is achieved, bringing a promising prospect for the large‐area device fabrication.     

Simultaneous Open‐Circuit Voltage Enhancement and Short‐Circuit Current Loss in Polymer: Fullerene Solar Cells Correlated by Reduced Quantum Efficiency for Photoinduced Electron Transfer

The limits of maximizing the open‐circuit voltage V_oc in solar cells based on poly[2,7‐(9,9‐didecylfluorene)‐alt‐5,5‐(4,7‐di‐2‐thienyl‐2,1,3‐benzothiadiazole)] (PF10TBT) as a donor using different fullerene derivatives as acceptor are investigated. Bulk heterojunction solar cells with PF10TBT and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) give a V_oc over 1 V and a power conversion efficiency of 4.2%. Devices in which PF10TBT is blended with fullerene bisadduct derivatives give an even higher V_oc, but also a strong decrease in short circuit current (J_sc). The higher V_oc is attributed to the higher LUMO of the acceptors in comparison to PCBM. By investigating the photophysics of PF10TBT:fullerene blends using near‐IR photo‐ and electroluminescence, time‐resolved photoluminescence, and photoinduced absorption we find that the charge transfer (CT) state is not formed efficiently when using fullerene bisadducts. Hence, engineering acceptor materials with a LUMO level that is as high as possible can increase V_oc, but will only provide a higher power conversion efficiency, when the quantum efficiency for charge transfer is preserved. To quantify this, we determine the CT energy (E_CT) and optical band gap (E_g), defined as the lowest first singlet state energy E_S1 of either the donor or acceptor, for each of the blends and find a clear correlation between the free energy for photoinduced electron transfer and J_sc. We find that E_g ? qV_oc > 0.6 eV is a simple, but general criterion for efficient charge generation in donor‐acceptor blends.     

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.     

Medium Bandgap Polymer Donor Based on Bi(trialkylsilylthienyl‐benzo[1,2‐b:4,5‐b′]‐difuran) for High Performance Nonfullerene Polymer Solar Cells

A new 2D‐conjugated medium bandgap donor–acceptor copolymer, J81 , based on benzodifuran with trialkylsilyl thiophene side chains as donor unit and fluorobenzothiazole as acceptor, is synthesized and successfully used in nonfullerene polymer solar cells (PSCs) with low bandgap n‐type organic semiconductor (n‐OS) 3,9‐bis(2‐methylene‐ (3‐(1,1‐dicyanomethylene)‐indanone)‐5,5,11,11‐tetrakis(4‐ hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]‐ dithiophene (ITIC) and m ‐ITIC as acceptor. J81 possesses a lower‐lying highest occupied molecular orbital (HOMO) energy level of ?5.43 eV and medium bandgap of 1.93 eV with complementary absorption in the visible–near infrared region with the n‐OS acceptor. The PSCs based on J81 :ITIC and J81 :m ‐ITIC yield high power conversion efficiency of 10.60% and 11.05%, respectively, with high V _oc of 0.95–0.96 V benefit from the lower‐lying HOMO energy level of J81 donor. The work indicates that J81 is another promising polymer donor for the nonfullerene PSCs.     

Printed Nonfullerene Organic Solar Cells with the Highest Efficiency of 9.5%

The current work reports a high power conversion efficiency (PCE) of 9.54% achieved with nonfullerene organic solar cells (OSCs) based on PTB7‐Th donor and 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene) (ITIC) acceptor fabricated by doctor‐blade printing, which has the highest efficiency ever reported in printed nonfullerene OSCs. Furthermore, a high PCE of 7.6% is realized in flexible large‐area (2.03 cm²) indium tin oxide (ITO)‐free doctor‐bladed nonfullerene OSCs, which is higher than that (5.86%) of the spin‐coated counterpart. To understand the mechanism of the performance enhancement with doctor‐blade printing, the morphology, crystallinity, charge recombination, and transport of the active layers are investigated. These results suggest that the good performance of the doctor‐blade OSCs is attributed to a favorable nanoscale phase separation by incorporating 0.6 vol% of 1,8‐diiodooctane that prolongs the dynamic drying time of the doctor‐bladed active layer and contributes to the migration of ITIC molecules in the drying process. High PCE obtained in the flexible large‐area ITO‐free doctor‐bladed nonfullerene OSCs indicates the feasibility of doctor‐blade printing in large‐scale fullerene‐free OSC manufacturing. For the first time, the open‐circuit voltage is increased by 0.1 V when 1 vol% solvent additive is added, due to the vertical segregation of ITIC molecules during solvent evaporation.     

Nitrile‐Substituted QA Derivatives: New Acceptor Materials for Solution‐Processable Organic Bulk Heterojunction Solar Cells

The development of non‐fullerene‐based electron acceptors (especially organic molecules with sufficient absorption property within the solar spectrum region) for bulk‐heterojunction (BHJ) organic solar cells (OSCs) is an important issue for the achievement of high photoconversion efficiency. In this contribution, a new class of organic acceptors di‐cyan substituted quinacridone derivatives (DCN‐nCQA, n = 4, 6 and 8) for BHJ solar cells was designed and synthesized. DCN‐nCQA molecules possess facile synthesis, solution processability, visible and near‐IR light absorption and relatively stable characteristics. The DCN‐8CQA molecule exhibited a proper LUMO energy level (–4.1 eV), small bandgap (1.8 eV) and moderate electron mobility (10^?4 cm² V^?1 S^?1), suggesting that this molecule is an ideal acceptor material for the classical donor material regio‐regular poly (3‐hexylthiophene) (P3HT). A photovoltaic device with a structure of [ITO/PEDOT:PSS/P3HT:DCN‐8CQA/LiF/Al] displayed a power conversion efficiency of 1.57% and a fill factor of 57% under 100 mW cm^?2 AM 1.5G simulated solar illumination. The DCN‐nCQA molecules showed remarkable absorption in the region from 650 to 700 nm, where P3HT has a weak absorption promoting overlap with the solar spectrum and potentially improving the performance of the solar cell.