High-performance Polymer Solar Cells Research Articles

High-Performance Polymer Solar Cells with Minimal Energy Loss Enabled by a Main-Chain-Twisted Nonfullerene Acceptor

We design and synthesize a new main-chain-twisted fused-ring narrow band gap n-type organic semiconductor acceptor (namely, IE4F-S) with a terminal group on the 4-position of 3-alkylthio-substitute...

A rational comparison of the effects of halogen atoms incorporated into the polymer donors on the performance of polymer solar cells

Despite the high performance polymer solar cells obtained by the fluorinated or chlorinated polymer donors, there is no effective guideline for how to choose a reasonable halogen atom incorporated into copolymer donors when designing organic photovoltaic materials. Two polymers of PBDT-F-3T2C containing F atom and PBDT-Cl-3T2C containing Cl atom are designed and synthesized. A direct comparison of the effects of fluorine and chlorine atom on the properties of the copolymer and resulting device performance is systematically studied. It can be found that both of the chlorine and fluorine atoms can effectively reduce the HOMO and LUMO levels, but chlorine atom is revealed to possess stronger downshifting ability for energy levels than fluorine atom in the copolymers. On the other hand, compared with the chlorine atom with larger atomic radius, the smaller fluorine atom possess strong self-assembly feature and negligible steric hindrance, enable the PBDT-F-3T2C with higher crystallinity and solution temperature-dependent aggregation behavior than PBDT-Cl-3T2C. The higher absorption coefficient, more favorable morphology, higher and more balanced charge mobilies endow the PBDT-F-3T2C with higher device performance than PBDT-Cl-3T2C (11.67% vs 10.19%). In addition, the performance of the 1,2,4-trimethylbenzene (TMB) solvent processed devices is also sensitive to halogenate atoms. An expressive PCE of 10.04% is obtained for F-containing devices, which is almost double higher than the Cl-containing devices. These results would provide a guideline for rational incorporation of halogen atoms into the polymer donors for high performance polymer solar cells. • Two polymer donors of PBDT-F-3T2C and PBDT-Cl-3T2C are designed and synthesized. • The effects of F and Cl atom on the properties of the polymers and PSCs. • A PCE of 11.67% obtained for halogenated solvent processed device. • Non-halogenated solvent processed devices yield a PCE over 10%.

A Simple Approach to Prepare Chlorinated Polymer Donors with Low-Lying HOMO Level for High Performance Polymer Solar Cells

Both photovoltaic performance and cost of materials are the key factors for commercial application of polymer solar cells (PSCs). In this study, we designed and synthesized two new conjugated polym...

Surface modification of ZnO electron transport layers with glycine for efficient inverted non-fullerene polymer solar cells

Abstract Interfacial engineering is crucial to improve the photovoltaic performance of polymer solar cells (PSCs). In this study, we demonstrate efficient inverted non-fullerene PSCs with ZnO modified by nontoxic glycine (Gly) as the electron transport layer (ETL). With the modification of Gly, work function of the ETL interlayer was decreased from 4.11 eV for ZnO to 4.02 eV for ZnO/Gly, which effectively increased the built-in electric field and hence improved the electron extraction. Furthermore, the surface energy of interlayer was also reduced from 69.1 mJ/m2 for ZnO to 52.5 mJ/m2, which is beneficial for the enrichment of the acceptor at the interface and hence facilities the electron transport and collection at cathode electrode. Therefore, the device based on PM6:IT-4F with ZnO/Gly as ETL exhibited a remarkably enhanced power conversion efficiency (PCE) of 14.0% relative to 12.9% for the control device with ZnO ETL, indicating a ∼9% increase of the PCE with the simple molecular modification of the ETL. Meanwhile, this strategy can also be successfully applied to other non-fullerene and fullerene based inverted PSCs. Our work provides an effective approach to modify ZnO for high performance PSCs.

Synergistic Effect of Chlorination and Selenophene: Achieving Elevated Solar Conversion in Highly Aggregated Systems

Chlorination and selenophene were used to develop benzothiadiazole-based polymers for high-performance polymer solar cells (PSCs). The introduction of selenophene can increase crystallinity due to the metalloid nature of selenium and thus facilitate charge transport. Chlorination can tune the energy levels and induce strong aggregation due to its unique features. A non-chlorinated polymer with selenophene, PBT3TSe, shows a highly crystalline structure and a dominant face-on orientation, consequently attaining a high short-circuit current (JSC). Chlorinated PBT3TClSe displays synergy between the advantages of chlorination and selenophene to achieve elevated photovoltaic performance, with a power conversion efficiency (PCE) approaching 9.89% in PC71BM-based devices. Interestingly, chlorination has an important influence on morphology of the polymer and polymer blend films, resulting in a severe aggregation and mixed face-on and edge-on orientation in the blend film. But the sufficient intermingling of donor...

Amino functionalized carbon nanotubes as hole transport layer for high performance polymer solar cells

In this work, we demonstrated the synthesis of amino functionalized MWNTs (af-MWNTs) via a simple and facile hydrothermal process and the af-MWNTs was acted as the hole transport layers (HTLs) of polymer solar cells (PSCs) based on active layers of Poly[N‑9″‑hepta‑decanyl‑2,7‑carbazolealt‑5,5‑(4′,7′‑di‑2‑thienyl‑2′,1′,3′‑benzothiadiazole)] (PCDTBT) and fullerene derivative [6,6]‑phenyl‑C71‑butyric acid methylester (PC71BM). Comparing with the control devices, devices based on af-MWNTs HLTs achieved an optimal power conversion efficiency (PCE) of 6.970%, leading to 17.6% enhancement comparing to the control device. The af-MWNTs HTLs exhibited remarkable enhancement on electrical conductivity, which was beneficial to the hole extraction and transport on interface. The enhancement of PCE was mainly attributed to the superior hole transport and extraction capabilities. Meanwhile, the af-MWNTs exhibited a suitable work function (WF) which was beneficial to hole extraction from the photoactive layer to the ITO anode. The experimental results indicated that the af-MWNTs HTLs not only presented excellent optical and electrical properties, but also played an important role for improving the efficiency of PSCs.

Enhancement of power conversion efficiency of bulk heterojunction polymer solar cells using core/shell, Au/graphene plasmonic nanostructure

Abstract We demonstrate power conversion efficiency improvement in polymer solar cells (PSCs) through incorporating gold nanoparticles with graphene shell (Au NPs@Gr), positioned between hole transport and active layers. Au NPs@Gr improves roughness and can penetrate to active layer, enhance optical absorption and induce more balanced charge transfer. Band gap of the donor was analyzed by Tauc's formula which showed band gap decline in Au@Gr-based solar cells (1.89 eV). Life time, recombination rate and bulk resistance were analyzed by impedance spectroscopy. Graphene shell over Au NPs incorporates in charge transport and the life time of the charges improved 80% when charge recombination resistance increased from 2.08 to 2.37 KΩ. Solar cell photovoltaic parameters also showed higher short circuit current (42%) and higher power conversion efficiency (100%) in comparison to reference. Results indicated that Au NPs@Gr structure can be considered as an effective material for high performance PSCs and future high-tech applications.

Photovoltaics literature survey (no. 149)

Photovoltaics literature survey (no. 149)

Fused nonacyclic electron acceptors with additional alkyl side chains for efficient polymer solar cells

Abstract Three new non-fullerene acceptors with the core of a fused nonacyclic unit, and the end-capping groups of 3-dicycanovinylindan-1-one are designed and synthesized for polymer solar cells. Those acceptor molecules bear four additional aliphatic side chains at the nonacyclic core, which endow them excellent solubility and crystallization-morphology tunability. Meanwhile, the effect of side chains’ size on the optical absorptions, electrochemical properties, and photovoltaic performance are carefully investigated. The results show that the bulk of side chains just slightly affects optical absorption and electronic energy levels, however, it significantly influences the molecular stacking and morphology separation, as well as the eventual device performance. When they are matched with the donor polymer poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione))] (PBDB-T), the device based on the acceptor with octyl group can deliver the best PCE of 8.57%, which overwhelms those based on other two acceptor materials. This can be attributed to the preferable nanophase separation for their blend films, and high and balanced charge mobility. The results highlight the important role of backbone and side-chain tailoring in designing non-fullerene acceptors towards high-performance polymer solar cells.

Conjugated Donor-Acceptor Terpolymers Toward High-Efficiency Polymer Solar Cells.

The development of conjugated alternating donor-acceptor (D-A) copolymers with various electron-rich and electron-deficient units in polymer backbones has boosted the power conversion efficiency (PCE) over 17% for polymer solar cells (PSCs) over the past two decades. However, further enhancements in PCEs for PSCs are still imperative to compensate their imperfect stability for fulfilling practical applications. Meanwhile development of these alternating D-A copolymers is highly demanding in creative design and syntheses of novel D and/or A monomers. In this regard, when being possible to adopt an existing monomer unit as a third component from its libraries, either a D' unit or an A' moiety, to the parent D-A type polymer backbones to afford conjugated D-A terpolymers, it will give a facile and cost-effective method to improve their light absorption and tune energy levels and also interchain packing synergistically. Moreover, the rationally controlled stoichiometry for these components in such terpolymers also provides access for further fine-tuning these factors, thus resulting in high-performance PSCs. Herein, based on their unique features, the recent progress of conjugated D-A terpolymers for efficient PSCs is reviewed and it is discussed how these factors influence their photovoltaic performance, for providing useful guidelines to design new terpolymers toward high-efficiency PSCs.

Morphological and Optical Engineering for High-Performance Polymer Solar Cells.

We demonstrate morphological and optical engineering by using processing additives and optical spacers for polymer solar cells. Among various processing additives, introduction of diphenyl ether (DPE)into the active layer results in the smoothest surface roughness with uniform and well-distributed donor/acceptor domains, and the device with DPE shows the highest device efficiency of 10.22% due to enhanced charge collection efficiency and minimized recombination loss. Additional ZnO optical spacers on the active layer controls the distribution of the electric field in the whole device and enhances the light absorption within the active layer, thereby improving device efficiency up to 10.81%.

N-Alkylation vs. O-alkylation: influence on the performance of the photovoltaic cells based on a tetracyclic lactam polymer donor.

Lactam-containing acceptors, which could provide two potential alkylation positions (N-alkylation and O-alkylation), are important building blocks for polymeric donors in high performance polymer solar cells (PSCs). However, the influence of alkylation positions on the PSC performance has seldom been studied. Herein, we investigated the influence of O-alkylation and N-alkylation on a novel bislactam acceptor, namely dibenzonaphthyridinedione (DBND), on the physical properties of the corresponding polymers and hence their PSC performance. Besides O-alkylated and N-alkylated DBND, half-N-alkylated-half-O-alkylated DBND (N,O-DBND) was also prepared and copolymerized with stannyl bithiophene (2T). It was found that by varying the alkylation positions, the optical, crystalline and aggregation properties of the corresponding polymers were greatly altered. In comparison with P(N-DBND-2T) and P(O-DBND-2T), P(N,O-DBND-2T) shows both better solubility and shorter π–π stacking distance. By blending with PC71BM, P(N,O-DBND-2T) forms better nano-fibrillar phase separation so that less charge recombination is observed, thus leading to a much better power conversion efficiency (PCE) around 5%, which is the highest value of the conjugated system based on N,O-alkylated acceptors. The results show that the asymmetric N,O-alkylation protocol is a promising way to adjust the properties of the bislactam-containing conjugated polymers.

Amorphous electron donors with controllable morphology for non-fullerene polymer solar cells

Amorphous polymeric donor, electron acceptor and donor:acceptor blend films for high performance polymer solar cells.

An A–D–D–A-type non-fullerene small-molecule acceptor with strong near-infrared absorption for high performance polymer solar cells

An A–D–D–A-type near-infrared non-fullerene small-molecule acceptor IDT2-DFIC with indacenodithiophene–indacenodithiophene (IDT2) as donating core and 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (2FIC) as electron withdrawing end groups has been synthesized.

A wide-bandgap D–A copolymer donor based on a chlorine substituted acceptor unit for high performance polymer solar cells

A new wide-bandgap chlorinated polymer, J101, was synthesized and successfully used as the donor polymer for application in non-fullerene PSCs, and the PSCs fabricated by combining the J101 donor with the electron acceptor ZITI demonstrated a remarkable PCE of 14.43%.

High-performance non-fullerene polymer solar cells based on naphthobistriazole wide bandgap donor copolymers

The non-fullerene polymer solar cells (NF-PSCs) devices based on the PFBTZNT:m-ITIC system exhibited a power conversion efficiency of up to 11.02%.

Nonfullerene acceptors with a novel nonacyclic core for high-performance polymer solar cells

Two nonfullerene acceptors (IDIDTT and IDIDTT-2F) with a novel nonacylic core were developed and applied in polymer solar cells for the first time.

Random D1–A1–D1–A2 terpolymers based on diketopyrrolopyrrole and benzothiadiazolequinoxaline (BTQx) derivatives for high-performance polymer solar cells

The overall power conversion efficiency of the polymer solar cell based on P13 (DPP/BTQx ratio is 1/1) showed the highest value of 9.20% with a Voc of 0.86 V, Jsc of 15.74 mA cm−2, and FF of 0.68.

Fluorene-fused ladder-type non-fullerene small molecule acceptors for high-performance polymer solar cells

FTTCN-based PSCs exhibited a PCE of 10.56%, with the highest FF of 73.82% for fluorene-based SMAs.

Energy level modulation of donor–acceptor alternating random conjugated copolymers for achieving high-performance polymer solar cells

Fine energy level modulation without negatively affecting other properties is realized for random conjugated copolymers, allowing rigorous investigation of the relationship of the chemical structure and device performance in solar cells.