Efficient Non-fullerene Polymer Research Articles

Cost-effective polymer donors based on pyridine for efficient nonfullerene polymer solar cells

Developing cost-effective polymer donors that can match nonfullerene acceptors is very important for practical applications of polymer solar cells (PSCs). In this work, low-cost 3-fluoropyridine and pyridine were employed as acceptor unit cores to construct cost-effective polymers PBDT-FPy, PBDT-Py and PBDF-Py by copolymerizing with commercially available donor units. PBDT-FPy, PBDT-Py and PBDF-Py show wide-bandgap of 2.08, 2.15 and 2.05 eV, respectively. Due to the strong electronegativity of nitrogen atom in pyridine and Nδ− … Hδ+ noncovalent dipole-dipole interactions, all polymers exhibit deep-lying highest-occupied molecular orbital (HOMO) energy levels, strong intermolecular π-π interaction and good planarity. The PBDT-FPy: Y6 based device exhibits a power conversion efficiency (PCE) of 8.34%, while the performance of PBDT-Py: Y6 and PBDF-Py: Y6 devices was significantly improved, with PCE of 10.02% and 10.00%. The results indicate that pyridine with simple structure and low synthetic cost is a promising building block to construct high-performance cost-effective polymer donors for application in PSCs.

High-performance nonfullerene polymer solar cells based on chlorinated quinoxaline copolymer with a high short-circuit current density

In organic solar cells, the absorption range and extinction coefficient of the active layer not only affect the charge separation and carrier transfer efficiency of excitons, but also influence the JSC, and thus the device efficiency. Herein, an efficient nonfullerene polymer solar cells (NF–PSCs) based on a medium-bandgap (MBG) polymer donor PBDTTS-TClQx comprising chlorinethiophene quinoxaline (Qx) unit and a small molecule nonfullerene acceptor (SM-NFA) Y6 is developed. The PBDTTS-TClQx shows a strong absorption in the wavelength region of 330∼750 nm with an optical band gaps (Egopt) of 1.68 eV, which is well complementary with that of Y6 (1.33 eV) and facilitates achieving of high short-circuit current (JSC) in PSCs. As a result, the PBDTTS-TClQx:Y6-based PSCs achieved a power conversion efficiency (PCE) of 14.28% with a JSC of 25.9 mA cm−2. The JSC of 25.9 mA cm−2 achieved is among the highest reported for Qx-based polymer donors in PSCs.

A polymer donor based on difluoro-quinoxaline with a naphthalimide substituent unit exhibits a low-lying HOMO level for efficient non-fullerene polymer solar cells.

The design and synthesis of polymer donors with a low-lying highest occupied molecular orbital (HOMO) level are crucial for increasing open-circuit voltages (VOC) and achieving high-performance non-fullerene polymer solar cells. Here, we developed two copolymers using non-fluorinated or fluorinated thienyl-conjugated benzodithiophenes as electron donor units, and difluoro-quinoxaline with a naphthalimide substituent (DNB) as the electron acceptor unit. These copolymers, namely PDNB and PDNB-2F, exhibited deep HOMO levels owing to the strong electron-withdrawing ability of the naphthalimide substituent. Density-functional theory calculations demonstrated that the skeletons of the two copolymers featured good coplanarity. Owing to the fluorination, PDNB-2F displayed an increased absorption coefficient and deeper HOMO level than PDNB. Moreover, the blended film based on PDNB-2F:Y6 demonstrated enhanced carrier mobility, decreased bimolecular recombination as well as favorable phase-separation regions. Consequently, the PDNB-2F:Y6-based device yielded a superior power conversion efficiency (PCE) of 12.18%, whereas the device based on PDNB:Y6 showed a comparatively lower PCE of 8.83%. These results indicate that difluoro-quinoxaline with a naphthalimide substituent is a prospective electron-deficient building block to develop donor polymers with low-lying HOMO levels to achieve efficient non-fullerene polymer solar cells.

Medium Bandgap Conjugated Polymers for Efficient Non-Fullerene Polymer Solar Cells; an In-Depth Study of Structural Diversity of Polymer Structure

Medium Bandgap Conjugated Polymers for Efficient Non-Fullerene Polymer Solar Cells; an In-Depth Study of Structural Diversity of Polymer Structure

Synergy strategy to the flexible alkyl and chloride side-chain engineered quinoxaline-based D–A conjugated polymers for efficient non-fullerene polymer solar cells

We are developing both copolymers with quinoxaline (Qx) as acceptor units by fine tuning the side chains with halogen atom chlorine (Cl) and flexible alkyl engineering for efficient non-fullerene polymer solar cells.

Induced crystallization of sol–gel-derived zinc oxide for efficient non-fullerene polymer solar cells

We demonstrate a novel strategy for induced crystallization of zinc oxide (ic-ZnO) that shows increased crystallinity relative to sol–gel derived zinc oxide, which is also proved to reduce the interfacial charge recombination efficiently in PSCs.

Wide bandgap donor polymers containing carbonyl groups for efficient non-fullerene polymer solar cells

Two wide bandgap conjugated polymers (PTCO8 and PTCO1) with different side chains, composed of alkylcarbonyl-substituted thiophene (TOC) as the electron-withdrawing unit and two-dimension benzodithiophene (BDT) as the electron-donating unit, are developed for non-fullerene polymer solar cells (PSCs). Relative to non-carbonyl-substituted control polymer PTC8, PTCO8 and PTCO1 exhibit a red-shifted absorption and deeper-lying highest occupied molecular orbital (HOMO) level. When blended with ITIC, the as-cast PTCO1-based devices yield a power conversion efficiency of up to 9.33% with an open-circuit voltage of 0.95 V, a short-circuit current density of 16.91 mA cm−2, and a fill factor of 57.9%, outperforming those of PTC8-based devices (4.04%) and PTCO8-based devices (5.91%). This work demonstrates that the carbonyl group is a promising electron-deficient moiety to construct wide-bandgap polymers for non-fullerene PSCs. Adjusting the length of side chains is a feasible strategy to improve PSC performance further.

Wide Band-gap Two-dimension Conjugated Polymer Donors with Different Amounts of Chlorine Substitution on Alkoxyphenyl Conjugated Side Chains for Non-fullerene Polymer Solar Cells

In this study, wide bandgap (WBG) two-dimensional (2D) copolymer donors (DZ1, DZ2, and DZ3) based on benzodithiophene (BDT) on alkoxyphenyl conjugated side chains without and with different amounts of chlorine atoms and difluorobenzotriazole (FBTZ) are designed and synthesized successfully for efficient non-fullerene polymer solar cells (PSCs). Three polymer donors DZ1, DZ2, and DZ3 display similar absorption spectra at 300–700 nm range with optional band-gap (Egopt) of 1.84, 1.92, and 1.97 eV, respectively. Compared with reported DZ1 without chlorine substitution, it is found that introducing chlorine atoms into the meta-position of the alkoxyphenyl group affords polymer possessing a deeper the highest occupied molecular orbital (HOMO) energy level, which can increase open circuit voltage (VOC) of PSCs, as well as improve hole mobility. Non-fullerene bulk heterojunction PSCs based on DZ2:MeIC demonstrate a relatively high power conversion efficiency (PCE) of 10.22% with a VOC of 0.88 V, a short-circuit current density (JSC) of 17.62 mA/cm2, and a fill factor (FF) of 68%, compared with PSCs based on DZ1:MeIC (a PCE of 8.26%) and DZ3:MeIC (a PCE of 6.28%). The results imply that adjusting chlorine atom amount on alkoxyphenyl side chains based on BDT polymer donors is a promising approach of synthesizing electron-rich building block for high performance of PSCs.

Shorter alkyl chain in thieno[3,4-c]pyrrole-4,6-dione (TPD)-based large bandgap polymer donors – Yield efficient non-fullerene polymer solar cells

Typically, conjugated polymers are composed of conjugated backbones and alkyl side chains. In this contribution, a cost-effective strategy of tailoring the length of alkyl side chain is utilized to design high-performing thieno[3,4-c]pyrrole-4,6-dione (TPD)-based large bandgap polymer donors PBDT-BiTPD(Cχ) (χ = 48, 52, 56), in which χ represents the alkyl side chain length in term of the total carbon number. A combination of light absorption, device, and morphology examinations make clear that the shorter alkyl side chains yield (i) higher crystallinity and more predominant face-on crystallite orientation in their neat and BHJ blend films, (ii) higher charge mobilities (6.7 × 10−4 cm2 V−1 s−1 for C48 vs. 3.2 × 10−4 cm2 V−1 s−1 for C56), and negligible charge recombination, consequently, (iii) significantly improved fill-factor (FF) and short current (JSC), while almost the same open circuit voltage (VOC) of ca. 0.82 V in their corresponding BHJ devices. In parallel, as alkyl side chain lengths decrease from C56 to C48, power conversion efficiencies (PCEs) increased from 7.8% for C56 to 11.1% for C52, and further to 14.1% for C48 in their BHJ solar cells made with a narrow bandgap non-fullerene acceptor Y6. This systematic study declares that shortening the side chain, if providing appropriate solubility in device solution processing solvents, is of essential significance for developing high-performing polymer donors and further improving device photovoltaic performance.

Solution‐Processed Polymer Solar Cells with over 17% Efficiency Enabled by an Iridium Complexation Approach

AbstractThe 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.

Asymmetric Siloxane Functional Side Chains Enable High-Performance Donor Copolymers for Photovoltaic Applications.

In this work, three benzodithiophene-benzotriazole alternated wide band gap copolymers attaching symmetric or asymmetric conjugated side chains, namely, PDBTFBTA-2T, PBDTFTBA-TSi, and PBDTFBTA-2Si, were developed for efficient nonfullerene polymer solar cells. The symmetry effect of the side chains was investigated in detail on the overall properties of these donor polymers. The results demonstrated that the introduced siloxane functional groups showed less effect on the absorption and frontier orbital levels of the prepared polymers but had a significant effect on the miscibility between these polymer donors and the nonfullerene acceptor. When increasing the content of siloxane functional groups, the miscibility of the polymer donors and Y6 would be improved, leading to the decreased domain size and more mixed domains. Interestingly, the active blend based on PBDTFTBA-TSi with asymmetric side chains exhibited more balanced miscibility, carrier mobility, and phase separation, benefiting exciton diffusion and dissociation. Therefore, a champion power conversion efficiency (PCE) of 14.18% was achieved finally in PBDTFTBA-TSi devices, which was 20.6 and 19.0% higher than the symmetric counterparts of PBTFBTA-2T devices (PCE = 11.76%) and PBDTFBTA-2Si devices (PCE = 11.92%), respectively. This work highlights that the asymmetric side-chain engineering based on siloxane functional groups is a promising design strategy for high-performance polymer donor semiconductors.

Subtle Polymer Donor and Molecular Acceptor Design Enable Efficient Polymer Solar Cells with a Very Small Energy Loss

AbstractA new wide bandgap polymer donor, PNDT‐ST, based on naphtho[2,3‐b:6,7‐b′]dithiophene (NDT) and 1,3‐bis(thiophen‐2‐yl)‐5,7‐bis(2‐ ethylhexyl)benzo[1,2‐c:4,5‐c′]dithiophene‐4,8‐dione (BDD) is developed for efficient nonfullerene polymer solar cells. To better match the energy levels, a new near infrared small molecule of Y6‐T is also developed. The extended π‐conjugation and less twist of PNDT‐ST provides it with higher crystallinity and stronger aggregation than the PBDT‐ST counterpart. The higher lowest occupied molecular orbital level of Y6‐T than Y6 favors the better energy level match with these polymers, resulting in improved open circuit voltage (Voc) and power conversion efficiency (PCE). The high crystallinity and strong aggregation of PNDT‐ST also induces large phase separation with poorer morphology, leading to lower fill factor and reduced PCE than PBDT‐ST. To mediate the crystallinity and optimize the morphology, PNDT‐ST and PBDT‐ST are blended together with Y6‐T, forming the ternary blend devices. As expected, the two compatible polymers allow continual optimization of the morphology by varying the blend ratio. The optimized ternary blend devices deliver a champion PCE as high as 16.57% with a very small energy loss (Eloss) of 0.521 eV. Such small Eloss is the best record for polymer solar cells with PCEs over 16% to date.

Fluorinated pyrazine-based D–A conjugated polymers for efficient non-fullerene polymer solar cells

Over the past decade, fluorinated materials have become the dominant donors for achieving high power conversion efficiencies in organic solar cells (OSCs).

Highly efficient non-fullerene polymer solar cells from a benzo[1,2-b:4,5-b′]difuran-based conjugated polymer with improved stabilities

A novel benzodifuran (BDF)-based polymer (PDiFPBDF-TBz, F13) was designed and synthesized for non-fullerene polymer solar cells with the impressive power conversion efficiencies of up to 13.34% and improved stabilities.

Optimization of processing solvent and film morphology to achieve efficient non-fullerene polymer solar cells processed in air

Efficient non-fullerene polymer solar cells based on P2F-EHp and ITIC derivatives were achieved by blade-coating under the ambient air conditions.

Difluorobenzoxadiazole-based conjugated polymers for efficient non-fullerene polymer solar cells with low voltage loss

Two donor-acceptor (D-A) conjugated copolymers based on difluorobenzoxadiazole (ffBX) and oligothiophenes, i.e. , PffBX-2T and PffBX-TT, were designed and synthesized for polymer solar cells (PSCs). Compared to the polymers based on difluorobenzothiadiazole (ffBT) units, the two ffBX-based polymers presented identical optical bandgaps (~1.62 eV), but lower highest occupied molecular orbital (HOMO) energy levels. Owing to the down-shifted HOMO levels, the PSCs based on PffBX-2T and PffBX-TT showed lower voltage loss, and the open-circuit voltage ( V oc ) was ~0.1 V higher than that of the devices with the ffBT-based polymer. As a result, higher photovoltaic performance was achieved for the devices based on the ffBX-based polymers. The power conversion efficiencies (PCEs) of the non-fullerene PSCs with PffBX-2T and PffBX-TT as the donor were 8.72% and 10.12%, respectively. The superior device performance of PffBX-TT resulted from the efficient exciton dissociation and charge transport as well as weak charge recombination, which could be ascribed to the favorable face-on packing of the conjugated backbones and the desired morphology in the blend film. Our study demonstrates that difluorobenzoxadiazole is a promising building block for constructing conjugated polymers for high-performance non-fullerene PSCs. • Difluorobenzoxadiazole-based polymers with alkylthiophene side chains were synthesized. • PffBX-2T and PffBX-TT based PSC devices showed low voltage loss of 0.54 and 0.52 V, respectively. • A high PCE up to 10.12% was achieved for PSC devices based on PffBX-TT.

Regioisomer‐Free Chlorinated Thiophene‐Based Ending Group for Thieno[3,2‐b]thiophene Central Unit‐Based Acceptor Enabling Highly Efficient Nonfullerene Polymer Solar Cells with High Voc Simultaneously

A pair of pure regioisomeric acceptor–donor–acceptor (A–D–A) typed nonfullerene small molecule acceptors (NF‐SMAs) (4TTIC and 4TTIC‐Cl), containing a central thieno[3,2‐b]thiophene‐sp3 hybridized “carbon‐bridge”‐based fused ring core unit and thiophene‐based IC or chlorinated thiophene‐based IC are synthesized for polymer solar cells (PSCs). Compared with 4TTIC, 4TTIC‐Cl not only achieves a red‐shifted absorption spectra and lower energy levels but also enhancement of molecular packing and crystallinity. The 4TTIC‐Cl‐based blend films display higher and more balanced charge carrier mobilities, more favorable morphology, and more efficient exciton dissociation in comparison with the 4TTIC‐based blend film. The optimized devices based on PBDB‐ST:4TTIC‐Cl deliver an impressively high power conversion efficiency (PCE) of 13.11% and fill factor of 74%, much higher than that of the PBDB‐ST:4TTIC‐based devices. Moreover, a small energy loss of ≈0.54 eV and a decent Voc of 0.88 V are simultaneously achieved for PBDB‐ST:4TTIC‐Cl‐based devices. Noticeably, the PCE of 13.11% is the highest reported value for NF‐SMAs containing the central thieno[3,2‐b]thiophene unit with sp3 hybridized carbon‐bridged cyclopentadiene fragments in binary PSCs. This study proves that introduction of less electron‐deficient thiophene‐based IC terminal group into thieno[3,2‐b]thiophene central core‐based SMAs is a very effective method for making high Voc and excellent PCE simultaneously.

Efficient non-fullerene polymer solar cells enabled by side-chain conjugated thieno[3,4-c]pyrrole-4,6-dione-based polymer and small molecular acceptors

The application of non-fullerene (NF) acceptors in bulk-heterojunction (BHJ) polymer solar cells (PSCs) is a promising approach to overcome the inherent drawbacks of fullerene derivatives-based acceptors. In PSCs, complementary absorption as well as matched molecular energy levels between the low bandgap acceptor-donor-acceptor (A-D-A) small molecular acceptor and medium/wide bandgap polymer donor is crucial to achieve high power conversion efficiency (PCE). Alternating polymers based on benzodithiophene (BDT) electron-donating segment and thieno[3,4-c]pyrrole-4,6-dione (TPD) electron-withdrawing segment own medium bandgap and low-lying highest occupied molecular orbital (HOMO) energy level, leading to presentable photovoltaic properties with fullerene derivatives. To probe into the performances of TPD-based polymers in NF-PSCs, two TPD-based polymers containing alkoxy or alkylthienyl modified benzo[1,2-b:4,5-b′]dithiophene (BDT) were synthesized and adopted as electron-donors and blended with A-D-A-type electron-acceptor 2,2′-[[6,6,12,12-tetrakis(4- hexylphenyl)-s-indacenodithieno[3,2-b]thiophene]methylidyne(3-oxo-1H-indene-2,1(3H)-diylidene)]]bis(propanedinitrile) (ITIC) to fabricate the corresponding photovoltaic devices. The two-dimensional conjugated polymer PBDTT-TPD shows enhanced extinction coefficient, deeper HOMO energy level and better hole transport performance, resulting in improved PCE of 6.17%. To further boost the performances of the polymers, a small molecular acceptor 2,2′-((2Z,2′Z)-((4,4,9,9-tetrahexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-2,7-diyl) bis(methanylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (IDIC) with down-shifted energy level was also used to blend with the two polymers in PSCs. Despite the open-circuit voltage (VOC) of the PBDTT-TPD:IDIC-based device is slightly decreased, the short-circuit current density (JSC) and fill factor (FF) are simultaneously improved, yielding an promising PCE of 7.15%. These results indicate that two-dimensional conjugated TPD-based polymers can be potential application as medium bandgap polymeric donor to match with small molecular acceptors having suitable molecular energy levels to get high efficiency in PSCs.

(Invited) Efficient Non-Fullerene Polymer Solar Cells

Polymer solar cell (PSCs) haveattracted much interest in the renewable energy field because of their low-cost manufacturing, light weight, flexibility and large-scale production [1, 2]. Conventional PSCs exhibit poor stability and short operational lifetimes under environment conditions, and thus require complex encapsulation process to reduce degradation under oxygen and moisture [3]. To solve those problems, PSCs with an inverted structure (iPSCs) were developed. In iPSCs, transition metal oxides such molybdenum oxide (MoO3) or vanadium oxide (V2O5) are used as the hole transport layer (HTL). On the other hand, titanium oxide (TiOx) and zinc oxide (ZnO) are used as electron transport layer (ETL) [4, 5]. In recent years, iPSCs with power conversion efficiency (PCE) of 11% has been reported [6]. Although fullerene derivatives (e. g PC71BM and PC61BM), have been widely used as acceptor materials, the interest on non-fullerene acceptors have increased because of their high thermal stability, tunable molecular energy levels, excellent optical absorption properties and low-cost synthesis [7, 8]. In this work, we present the fabrication and the analysis of the performance of iPSCs based on the polymer PBDB-T and the non-fullerene acceptor IT-M. All the devices were fabricated on ITO substrate using TiOx as ETL, while the V2O5/Ag bilayer was used as top cathode. The materials PBDB-T:IT-M were dissolved in a mixture of solvents chlorobenzene and 1,8-diiodooctane (99:0.5 v/v) with the total concentration of 20 mg ml-1. The PBDB-T:IT-M blend solution was spin-cast on top of TiOx at two different velocities to analyze the effect of the active layer thickness (100 and 130nm) on the performance parameters of iPSCs. Moreover, the effects of the annealing temperature (0, 100 and 160ºC) on the performance parameters of PBDB-T:IT-M-based devices are also investigated. Current density–voltage (J–V) characteristics were measured under simulated AM1.5G illumination (100mWcm-2) conditions to calculate the performance parameters [open circuit voltage (VOC), short-circuit current density (JSC), fill factor (FF) and power conversion efficiency (PCE)] of all iPSCs. The devices with an active layer with a thickness of 100nm exhibit higher performance parameter than that of devices with an active layer thickness of 130nm. In both type of devices (active layer thickness of 100 and 130 nm), the performance parameter values decrease as the annealing temperature increases. Devices with an active layer thickness of 100nm and without thermal annealing (0ºC) exhibit the highest performance parameters, VOC= 919 mV, JSC= 16.2 mA cm-2, FF = 67% with an a PCE of about 9.9%. The results demonstrated that iPSCs using non-fullerene acceptor allow to reach efficiencies of about 10% after a manufacturing parameters optimization such as thickness of the active layer and annealing temperature.Moreover, we demonstrated that thermal annealing reduces the performance of these devices. Finally, this work shown the fabrication and characterization of high efficiency PSCs using a non-fullerene acceptor material as a promisingalternative to the fabrication of fullerene-based PSC. Acknowledgements This work was supported by the Spanish Ministry of Economy, Industry and Competitiveness (MEIC) for grant numbers, TEC2015-71915-REDT and TEC2015-71324-R (MINECO/FEDER), by the ICREA for the ICREA Academia Award, by the Catalan authority for project AGAUR 2017 SGR 1527. References S. Balderrama, F. Avila-Herrera, J. G. Sanchez, J. Pallares, O. Vigil-Galan, L. F. Marsal, M. Estrada, IEEE J. Photovoltaics, 6, 2, 491–497, 2016.D. Nielsen, C. Cruickshank, S. Foged, J. Thorsen, F. C. Krebs, Sol. Energy Mater. Sol. Cells, 94, 10, 1553–1571, 2010.S. Balderrama, M. Estrada, P. L. Han, P. Granero, J. Pallarés, J. Ferré-Borrull, L. F. Marsal, Sol. Energy Mater. Sol. Cells,125, 155–163, 2014.G. Sánchez, V. S. Balderrama, M. Estrada, E. Osorio, J. Ferré-Borrull, L. F. Marsal, J. Pallarès, Sol. Energy,150, 147–155, 2017.G. Sánchez, V. S. Balderrama, S. I. Garduño, E. Osorio, A. Viterisi, M. Estrada, J. Ferré-Borrull, J. Pallarès, L. F. Marsal, RSC Adv., 8, 24, 13094–13102, 2018.S. Balderrama, J. G. Sánchez, G. Lastra, W. Cambarau, S. Arias, J. Pallarès, E. Palomares, M. Estrada, L. F. Marsal, J. Mater. Chem. A, 6, 45, 2018.Cheng, G. Li, X. Zhan, and Y. Yang, Nat. Photonics, 12, 3, 131–142, 2018.Yan, S. Barlow, Z. Wang, H. Yan, A. K.-Y. Jen, S. R. Marder, and X. Zhan, Nat. Rev. Mater., 3, 3, 18003, 2018. Figure 1

Enhancing the electron blocking ability of n-type MoO3 by doping with p-type NiO for efficient nonfullerene polymer solar cells

Abstract MoO3 is a promising n-type anode interfacial layer (AIL) with high work function for polymer solar cells (PSCs). However, due to the limited electron blocking ability of n-type metal oxide, the interfacial recombination occurs inevitably in the MoO3/organic interface. Herein, we for the first time strategically introduced minimal amount of p-type NiOx into n-type MoO3 to enhance the electron blocking ability of AIL. The MoO3 doped with NiOx layer (MoO3:NiOx) is highly transparent with a conduction band of 3.25 eV and a work function of 5.10 eV, which prolongs the electron lifetime of PBDB-T:IT-M based device from 0.63 to 5.05 μs. Benefiting from the prolonged lifetime and enhanced charge collection of MoO3:NiOx AIL, the average power conversion efficiency (PCE) of PBDB-T:IT-M based devices is significantly improved to 10.81%, much higher than that of control devices with PEDOT:PSS (9.79%), MoO3 (8.97%) and NiOx (9.51%) AILs. Our findings provide a new approach to tuning the energy level of cost-efficient and simply processed metal oxide interfacial materials for high performance and stable nonfullerene PSCs.