Mechanistic Investigation into Dynamic Function of Third Component Incorporated in Ternary Near‐Infrared Nonfullerene Organic Solar Cells

Organic solar cells (OSCs) consisting of an ultralow‐bandgap nonfullerene acceptor (NFA) with an optical absorption edge that extends to the near‐infrared (NIR) region are of vital interest to semitransparent and tandem devices. However, huge energy‐loss related to inefficient charge dissociation hinders their further development. The critical issues of charge separation as exemplified in NIR‐NFA OSCs based on the paradigm blend of PTB7–Th donor (D) and IEICO–4F acceptor (A) are revealed here. These studies corroborate efficient charge transfer between D and A, accompanied by geminate recombination of photo‐excited charge carriers. Two key factors restricting charge separation are unveiled as the connection discontinuity of individual phases in the blend and long‐lived interfacial charge‐transfer states (CTS). By incorporation of a third‐component of benchmark ITIC or PC₇₁BM with various molar ratios, these two issues are well‐resolved accordingly, yet in distinctly influencing mechanisms. ITIC molecules modulate film morphology to create more continuous paths for charge transportation, whereas PC₇₁BM diminishes CTS and enhances electron transfer at the D/A interfaces. Consequently, the optimal untreated ternary OSCs comprising 0.3 wt% ITIC and 0.1 wt% PC₇₁BM in the blend deliver higher J_SC values of 21.9 and 25.4 mA cm^‐2, and hence increased PCE of 10.2% and 10.6%, respectively.     

Influence of Blend Morphology and Energetics on Charge Separation and Recombination Dynamics in Organic Solar Cells Incorporating a Nonfullerene Acceptor

Nonfullerene acceptors (NFAs) in blends with highly crystalline donor polymers have been shown to yield particularly high device voltage outputs, but typically more modest quantum yields for photocurrent generation as well as often lower fill factors (FF). In this study, we employ transient optical and optoelectronic analysis to elucidate the factors determining device photocurrent and FF in blends of the highly crystalline donor polymer PffBT4T‐2OD with the promising NFA FBR or the more widely studied fullerene acceptor PC₇₁BM. Geminate recombination losses, as measured by ultrafast transient absorption spectroscopy, are observed to be significantly higher for PffBT4T‐2OD:FBR blends. This is assigned to the smaller LUMO‐LUMO offset of the PffBT4T‐2OD:FBR blends relative to PffBT4T‐2OD:PC₇₁BM, resulting in the lower photocurrent generation efficiency obtained with FBR. Employing time delayed charge extraction measurements, these geminate recombination losses are observed to be field dependent, resulting in the lower FF observed with PffBT4T‐2OD:FBR devices. These data therefore provide a detailed understanding of the impact of acceptor design, and particularly acceptor energetics, on organic solar cell performance. Our study concludes with a discussion of the implications of these results for the design of NFAs in organic solar cells.     

Single Crystal Microwires of p‐DTS(FBTTh2)2 and Their Use in the Fabrication of Field‐Effect Transistors and Photodetectors

Single crystal microwires of a well‐studied organic semiconductor used in organic solar cells, namely p‐DTS(FBTTh₂)₂, are prepared via a self‐assembly method in solution. The high level of intermolecular organization in the single crystals facilitates migration of charges, relative to solution‐processed films, and provides insight into the intrinsic charge transport properties of p‐DTS(FBTTh₂)₂. Field‐effect transistors based on the microwires can achieve hole mobilities on the order of ≈1.8 cm² V^?1 s^?1. Furthermore, these microwires show photoresponsive electrical characteristics and can act as photoswitches, with switch ratios over 1000. These experimental results are interpreted using theoretical simulations using an atomistic density functional theory approach. Based on the lattice organization, intermolecular couplings and reorganization energies are calculated, and hole mobilities for comparison with experimental measurements are further estimated. These results demonstrate a unique example of the optoelectronic applications of p‐DTS(FBTTh₂)₂ microwires.     

Revealing the effect of donor/acceptor intermolecular arrangement on organic solar cells performance based on two-dimensional conjugated small molecule as electron donor

A series of solution processed organic solar cells (OSCs) were fabricated with a two-dimensional conjugated small molecule SMPV1 as electron donor and fullerene derivatives PC₇₁BM or ICBA as electron acceptor. The champion power conversion efficiency (PCE) of OSCs arrives to 7.05% for the cells with PC₇₁BM as electron acceptor. A relatively large open circuit voltage (V_OC) of 1.15 V is obtained from cells using ICBA as electron acceptor with an acceptable PCE of 2.54%. The fill factor (FF) of OSCs is 72% or 61% for the cells with PC₇₁BM or ICBA as electron acceptor, which is relatively high value for small molecule OSCs. The relatively low performance of OSCs with ICBA as electron acceptor indicates that ICBA cannot play positive role in photoelectric conversion processes, which is very similar to the phenomenon observed from the OSCs with high efficient narrow band gap polymers other than P3HT as electron donor, the underlying reason is still in debate. The SMPV1 has strong self-assemble ability to form an ordered two dimensional lamellar structure, which provides an effective platform to investigate the effect of electron acceptor chemical structure on the performance of OSCs. Experimental results exhibit that ICBA molecules may prefer to vertical cross-intercalation among side chains of SMPV1, PC₇₁BM molecules may have better miscibility with SMPV1 in the active layer. The different donor/acceptor (D/A) intermolecular arrangement strongly influences photon harvesting, exciton dissociation and charge carrier transport, which may provide a new sight on performance improvement of OSCs by adjusting D/A intermolecular arrangements.     

Competitive Absorption and Inefficient Exciton Harvesting: Lessons Learned from Bulk Heterojunction Organic Photovoltaics Utilizing the Polymer Acceptor P(NDI2OD‐T2)

Organic solar cells utilizing the small molecule donor 7,7′‐(4,4‐bis(2‐ethylhexyl)‐4H‐silolo[3,2‐b:4,5‐b′]dithiophene‐2,6‐diyl)bis(6‐fluoro‐4‐(5′‐hexyl‐[2,2′‐bithiophen]‐5‐yl)benzo[c][1,2,5] thiadiazole) (p‐DTS(FBTTh₂)₂ and the polymer acceptor poly{[N,N′‐bis(2‐octyldodecyl)‐1,4,5,8‐naphthalenedicarboximide‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene)}(P(NDI2OD‐T2)) are investigated and a power conversion efficiency of 2.1% is achieved. By systematic study of bulk heterojunction (BHJ) organic photovoltaic (OPV) quantum efficiency, film morphology, charge transport and extraction and exciton diffusion, the loss processes in this blend is revealed compared to the blend of [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC₇₁BM) and the same donor. An exciton diffussion study using Förster resonant energy transfer (FRET) shows the upper limit of the P(NDI2OD‐T2) exciton diffusion length to be only 1.1 nm. The extremely low exciton diffusion length of P(NDI2OD‐T2), in combination with the overlap in donor and acceptor absorption, is then found to significantly limit device performance. These results suggest that BHJ OPV devices utilizing P(NDI2OD‐T2) as an acceptor material will likely be limited by its low exciton diffusion length compared to devices utilizing functionalized fullerene acceptors, especially when P(NDI2OD‐T2) significantly competes with the donor molecule for photon absorption.     

Charge Photogeneration for a Series of Thiazolo‐Thiazole Donor Polymers Blended with the Fullerene Electron Acceptors PCBM and ICBA

Photoinduced charge separation in bulk heterojunction solar cells is studied using a series of thiazolo‐thiazole donor polymers that differ in their side groups (and bridging atoms) blended with two acceptor fullerenes, phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) and a fullerene indene‐C60 bisadduct (ICBA). Transient absorption spectroscopy is used to determine the yields and lifetimes of photogenerated charge carriers, complimented by cyclic voltammetry studies of materials energetics, wide angle X‐ray diffraction and transmission electron microscopy studies of neat and blend film crystallinity and photoluminescence quenching studies of polymer/fullerene phase segregation, and the correlation of these measurements with device photocurrents. Good correlation between the initial polaron yield and the energetic driving force driving charge separation, ΔE_CS is observed. All blend films exhibit a power law transient absorption decay phase assigned to non‐geminate recombination of dissociated charges; the amplitude of this power law decay phase shows excellent correlation with photocurrent density in the devices. Furthermore, for films of one (relatively amorphous) donor polymer blended with ICBA, we observe an additional 100 ns geminate recombination phase. The implications of the observations reported are discussed in terms of the role of materials' crystallinity in influencing charge dissociation in such devices, and thus materials design requirements for efficient solar cell function.     

Efficient Ternary Organic Solar Cells Enabled by the Integration of Nonfullerene and Fullerene Acceptors with a Broad Composition Tolerance

The ternary structure that combines fullerene and nonfullerene acceptors in a photoactive layer is demonstrated as an effective approach for boosting the power conversion efficiencies (PCEs) of organic solar cells (OSCs). Here, highly efficient ternary OSCs comprising a wide‐bandgap polymer donor (PBT1‐C), a narrow‐bandgap nonfullerene acceptor (IT‐2F), and a typical fullerene derivative (PC₇₁BM) are reported. It is found that the addition of PC₇₁BM into the PBT1‐C:IT‐2F blend not only increases the device efficiency up to 12.2%, but also improves the ambient stability of the OSCs. Detailed investigations indicate that the improvement in photovoltaic performance benefits from synergistic effects of increased photon‐harvesting, enhanced charge separation and transport, suppressed trap‐assisted recombination, and optimized film morphology. Moreover, it is noticed that such a ternary system exhibits excellent tolerance to the PC₇₁BM component, for which PCEs over 11.2% can be maintained throughout the whole blend ratios, higher than that (11.0%) of PBT1‐C:IT‐2F binary reference device.     

Boosting Performance of Non‐Fullerene Organic Solar Cells by 2D g‐C3N4 Doped PEDOT:PSS

The power‐conversion efficiency (PCE) of single‐junction organic solar cells (OSCs) has exceeded 16% thanks to the development of non‐fullerene acceptor materials and morphological optimization of active layer. In addition, interfacial engineering always plays a crucial role in further improving the performance of OSCs based on a well‐established active‐layer system. Doping of graphitic carbon nitride (g‐C₃N₄) into poly(3,4‐ethylene‐dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a hole transport layer (HTL) for PM6:Y6‐based OSCs is reported, boosting the PCE to almost 16.4%. After being added into the PEDOT:PSS, the g‐C₃N₄ as a Bronsted base can be protonated, weakening the shield effect of insulating PSS on conductive PEDOT, which enables exposures of more PEDOT chains on the surface of PEDOT:PSS core‐shell structure, and thus increasing the conductivity. Therefore, at the interface between g‐C₃N₄ doped HTL and PM6:Y6 layer, the charge transport is improved and the charge recombination is suppressed, leading to the increases of fill factor and short‐circuit current density of devices. This work demonstrates that doping g‐C₃N₄ into PEDOT:PSS is an efficient strategy to increase the conductivity of HTL, resulting in higher OSC performance.     

New m-alkoxy-p-fluorophenyl difluoroquinoxaline based polymers in efficient fullerene solar cells with high fill factor

Two new donor (D) - acceptor (A) copolymers, named m-O-p-F-DFQx-BDT (OFQx-T) and m-EH-p-F-DFQx-BDT (EHFQx-T), which were based on meta-octyloxy-para-fluorophenyl and meta-ethylhexyloxy-para-fluorophenyl difluoroquinoxaline as acceptor units (O-DFQx/EH-DFQx) and alkylthienyl substituted benzodithiophene (BDT) as a donor unit, were designed and synthesized. EHFQx-T had higher absorption coefficient than OFQx-T which contributed to larger short-circuit current density (J_sc). EHFQx-T showed a lower the highest occupied molecular orbital (HOMO) which is beneficial for the voltage open-circuit (V_oc). The polymer solar cells (PSCs) based OFQx-T:PC₇₁BM and EHFQx-T:PC₇₁BM blended film as active layer showed high power conversion efficiency (PCE) of 7.60% and 8.44%, respectively, with 1,8-diiodooctane (DIO) solvent additive treatment. More importantly, OFQx-T:PC₇₁BM and EHFQx-T:PC₇₁BM had good fill factor (FF), especially the FF of OFQx-T:PC₇₁BM was over 70%. The high FF contributed to obtain high PCEs for OFQx-T and EHFQx-T. The more balanced and higher charge mobility, smaller geminate recombination and suitable nanoscale phase separation size of EHFQx-T demonstrate that changing octyl chain to ethylhexyl chain in DFQx acceptor unit is efficient to improve photovoltaic properties in fullerene solar cells.     

Molecular Orientation Unified Nonfullerene Acceptor Enabling 14% Efficiency As‐Cast Organic Solar Cells

Molecular orientation and π–π stacking of nonfullerene acceptors (NFAs) determine its domain size and purity in bulk‐heterojunction blends with a polymer donor. Two novel NFAs featuring an indacenobis(dithieno[3,2‐b:2?,3?‐d]pyrrol) core with meta‐ or para‐alkoxyphenyl sidechains are designed and denoted as m‐INPOIC or p‐INPOIC , respectively. The impact of the alkoxyl group positioning on molecular orientation and photovoltaic performance of NFAs is revealed through a comparison study with the counterpart ( INPIC‐4F ) bearing para‐alkylphenyl sidechains. With inward constriction toward the conjugated backbone, m‐INPOIC presents predominant face‐on orientation to promote charge transport. The as‐cast organic solar cells (OSCs) by blending m‐INPOIC and PBDB‐T as active layers exhibit a power conversion efficiency (PCE) of 12.1%. By introducing PC₇₁BM as the solid processing‐aid, the ternary OSCs are further optimized to deliver an impressive PCE of 14.0%, which is among the highest PCEs for as‐cast single‐junction OSCs reported in literature to date. More attractively, PBDB‐T: m‐INPOIC :PC₇₁BM based OSCs exhibit over 11% PCEs even with an active layer thickness over 300 nm. And the devices can retain over 95% of PCE after storage for 20 days. The outstanding tolerance to film thickness and outstanding stability of the as‐cast devices make m‐INPOIC a promising candidate NFA for large‐scale solution‐processable OSCs.     

Efficient DPP Donor and Nonfullerene Acceptor Organic Solar Cells with High Photon‐to‐Current Ratio and Low Energetic Loss

The high crystallinity and ability to harvest near‐infrared photons make diketopyrrolopyrrole (DPP)‐based polymers one of the most promising donors for high performing organic solar cells (OSCs). However, DPP‐based OSC devices still suffer from the trade‐off between energetic loss (E_loss) and maximum external quantum efficiency (EQE_max), which significantly hinders their potential. Thus far, the replacement of fullerenes with small molecule acceptors did not wisdom the performance development of DPP‐donor‐based solar cells due to severe charge recombination issues. In this work, efficient DPP‐based solar cells are reported using low bandgap fused ring electron acceptor, IEICO‐4F. PBDTT‐DPP:IEICO‐4F OSC devices deliver a champion power conversion efficiency of 9.66% with successful interface engineering along with low E_loss of 0.57 eV and a high EQE_max (>70%).     

High-Performance Ternary Organic Solar Cells Enabled by Integrating a 3D-Shaped Guest Acceptor Derived from Perylene Diimide

Integrating a third component into the binary system is considered to be one of the most effective strategies to further enhance the power conversion efficiency (PCE) in organic solar cells (OSCs). Here, a novel perylene diimide (PDI) derivative featuring 3D structure, TPA-4PDI, with tetraphenyladamantane central core is developed as a guest electron acceptor to be incorporated into the PM6:Y6 binary system. The champion PCE of ternary OSC is recorded to be 18.29% by adding 7.5 wt.% of TPA-4PDI in the ternary blend, which photovoltaic performance is enhanced with synergistically increased open-circuit voltage (V_oc) of 0.849 V, short-circuit current density (J_sc) of 27.55 mA cm⁻², and fill factor (FF) of 78.21%. TPA-4PDI exhibits a complementary absorption band with PM6 and Y6 while its lowest unoccupied molecular orbital (LUMO) energy level falls between the two host materials. The addition of TPA-4PDI can effectively suppress the recombination behavior, inhibit the excessive aggregation of Y6 and improve the morphology of PM6:Y6 blend. All these effects function synergistically and then lead to the enhancement of V_oc, J_sc, and FF in ternary OSCs. This study suggests that developing PDI derivatives as the third component is an effective method to further improve the performance of ternary OSCs.     

Enhancing efficiency for additive–free blade–coated small–molecule solar cells by thermal annealing

Blade coating was successfully applied to realise high-efficiency small-molecule organic solar cells (OSCs) with a solution-processed active layer comprising a small organic molecule DR3TBDTT with a benzo[1,2–b:4,5–b′]dithiophene (BDT) unit as the central building block as the donor and [6,6]–phenyl–C71–butyric acid methyl ester (PC₇₁BM) as the acceptor. Using chloroform as the solvent, a DR3TBDTT/PC₇₁BM blend active layer without an additive was effectively formed through blade coating. The power conversion efficiency (PCE) of small organic molecule solar cells was enhanced by 3.7 times through thermal annealing at 100 °C. This method produces OSCs with a high PCE of up to 6.69%, with an open circuit voltage (V_oc) of 0.97 V, a short-circuit current density (J_sc) of 12.60 mA/cm², and a fill factor (FF) of 0.55.     

Achieving Organic Solar Cells with an Efficiency of 18.80% by Reducing Nonradiative Energy Loss and Tuning Active Layer Morphology

The efficiency of organic solar cells (OSCs) is primarily limited by their significant nonradiative energy loss and unfavorable active layer morphology. Achieving high-efficiency OSCs by suppressing nonradiative energy loss and tuning the active layer morphology remains a challenging task. In this study, an acceptor named CH-ThCl is designed, featuring an extended conjugation central core, dichlorodithienoquinoxaline. The incorporation of chlorine-substituted extended conjugation in the central core enhances the acceptor's rigidity and promotes J-aggregation, leading to improved molecular luminescent efficiency and a reduction in nonradiative energy loss. A binary device based on PM6: CH-ThCl demonstrates a power conversion efficiency (PCE) of 18.16% and exhibits a high open-circuit voltage (V_oc) of 0.934 V, attributed to the remarkably low nonradiative energy loss of 0.21 eV. Furthermore, a ternary device is fabricated by incorporating CH-6F as the third component, resulting in a significantly enhanced PCE of 18.80%. The ternary device exhibits improvements in short-circuit current (J_sc) and fill factor (FF) while maintaining the V_oc, primarily due to the optimized active layer morphology. These results highlight the effectiveness of combining the reduction of nonradiative energy loss and precise tuning of the active layer morphology as a viable strategy for achieving high-efficiency OSCs.     

High-performance alloy-like ternary organic solar cells with two compatible non-fullerene acceptors

Ternary blending is one of the effective strategies to modulate the blend film morphology for achieving high efficiency organic solar cells (OSCs). In this work, high-performance ternary OSCs are fabricated by introducing a non-fullerene acceptor, namely IDTP-4F into the PM6:Y6 binary system to enhance the device performance. Detailed investigations indicate that IDTP-4F can form an alloy phase with Y6, resulting in the optimized morphology, which can facilitate the charge transport and reduce recombination, leading to enhanced open-circuit voltage (V_oc) and fill factor (FF) simultaneously. Consequently, the optimized ternary OSCs exhibit an excellent power conversion efficiency (PCE) of 17.1%, which is much higher than that of PM6:Y6 binary OSCs (15.9%). These results indicate that combining two compatible non-fullerene acceptors is an effective strategy to fabricate high efficiency ternary OSCs.     

18.9% Efficiency Ternary Organic Solar Cells Enabled by Isomerization Engineering of Chlorine-Substitution on Small Molecule Donors

Ternary organic solar cells (OSCs) represent an efficient and facile strategy to further boost the device performance. However, the selection criteria and rational design of the third guest small molecule (SM) material still remain less understood. In this study, two new SM donor isomers, with α-chlorinated thiophene (αBTCl) and β-chlorinated thiophene (βBTCl) as side chains, are systematically designed, synthesized and incorporated as a third component in PM6:L8-BO binary blends. It is noticed that introducing the SM donors guest has extended the absorption of photo-active layer, induced desired component distribution vertically with enhanced crystallinity and reduced recombination process, leading to increased short-circuit current (J_SC) and improved fill factor. Moreover, due to the synergetic suppressed nonradiative loss and preferable morphology, the ternary OSCs feature improves open-circuit voltage (V_OC). Consequently, an impressive champion power conversion efficiency of 18.96% and 18.55% is achieved by αBTCl-based and βBTCl-based ternary OSCs, respectively. Furthermore, a record efficiency of 17.46% is obtained with a 330 nm thickness of αBTCl-based ternary OSCs. This study demonstrates that molecular isomerization can be a promising design approach for SM donors to construct high-performance ternary OSCs with simultaneous enhancement of all photovoltaic parameters.     

Influence of Phase Segregation on Recombination Dynamics in Organic Bulk‐Heterojunction Solar Cells

The recombination dynamics of charge carriers in organic bulk‐heterojunction (BHJ) solar cells made of the blend system poly(2,5‐bis(3‐dodecylthiophen‐2‐yl)thieno[2,3‐b]thiophene) (pBTCT‐C₁₂):[6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) with a donor–acceptor ratio of 1:1 and 1:4 are studied here. The techniques of charge‐carrier extraction by linearly increasing voltage (photo‐CELIV) and, as local probe, time‐resolved microwave conductivity are used. A difference of one order of magnitude is observed between the two blends in the initially extracted charge‐carrier concentration in the photo‐CELIV experiment, which can be assigned to an enhanced geminate recombination that arises through a fine interpenetrating network with isolated phase regions in the 1:1 pBTCT‐C₁₂:PC₆₁BM BHJ solar cells. In contrast, extensive phase segregation in 1:4 blend devices leads to an efficient polaron generation that results in an increased short‐circuit current density of the solar cells. For both studied ratios a bimolecular recombination of polarons is found using the complementary experiments. The charge‐carrier decay order of above two for temperatures below 300 K can be explained on the basis of a release of trapped charges. This mechanism leads to delayed bimolecular recombination processes. The experimental findings can be generalized to all polymer:fullerene blend systems allowing for phase segregation.     

High‐Performance Pseudoplanar Heterojunction Ternary Organic Solar Cells with Nonfullerene Alloyed Acceptor

The vast majority of ternary organic solar cells are obtained by simply fabricating bulk heterojunction (BHJ) active layers. Due to the inappropriate distribution of donors and acceptors in the vertical direction, a new method by fabricating pseudoplanar heterojunction (PPHJ) ternary organic solar cells is proposed to better modulate the morphology of active layer. The pseudoplanar heterojunction ternary organic solar cells (P‐ternary) are fabricated by a sequential solution treatment technique, in which the donor and acceptor mixture blends are sequentially spin‐coated. As a consequence, a higher power conversion efficiency (PCE) of 14.2% is achieved with a V_oc of 0.79 V, J_sc of 25.6 mA cm^?2, and fill factor (FF) of 69.8% compared with the ternary BHJ system of 13.8%. At the same time, the alloyed acceptor is likely formed between two the acceptors through a series of in‐depth explorations. This work suggests that nonfullerene alloyed acceptor may have great potential to realize effective P‐ternary organic solar cells.     

Synthesis and photophysical properties of semiconductor molecules D1-A-D2-A-D1-type structure based on derivatives of quinoxaline and dithienosilole for organics solar cells

A novel small molecule with D1-A-D2-A-D1 structure denoted as DTS(QxHT₂)₂ based on quinoxaline acceptor and dithienosilone donor units was synthesized and its optical and electrochemical properties were investigated. The thin film of DTS(QxHT₂)₂ showed a broad absorption profile covering the solar spectrum from 350 nm to 780 nm with an optical bandgap of 1.63 eV. The energy levels estimated from the cyclic voltammetry indicate that this small molecule is suitable as donor along with PC₇₁BM as acceptor for the fabrication solution processed bulk heterojunction solar cells for efficient exciton dissociation and high open circuit voltage. The organic solar cells based on optimized DTS(QxHT2)2:PC₇₁BM active layers processed with chloroform and DIO/CF showed overall power conversion efficiency of 3.16% and 6.30%, respectively. The higher power conversion efficiency of the solar cell based on the DIO/CF processed active layer is attributed to enhanced short circuit photocurrent and fill factor may be related to better phase separation between donor and acceptor in the active layer and more balanced charge transport, induced by the solvent additive. The power conversion efficiency of the organic solar cell was further improved up to 7.81% based on active layer processed with solvent additive, using CuSCN as hole transport layer instead of PEDOT:PSS and mainly attributed to increased fill factor and open circuit voltage due the formation of better Ohmic contact between the active layer and the CuSCN layer.     

Highly Efficient Ternary Solar Cells with Efficient Förster Resonance Energy Transfer for Simultaneously Enhanced Photovoltaic Parameters

Introducing a third component into organic bulk heterojunction solar cells has become an effective strategy to improve photovoltaic performance. Meanwhile, the rapid development of non-fullerene acceptors (NFAs) has pushed the power conversion efficiency (PCE) of organic solar cells (OSCs) to a higher standard. Herein, a series of fullerene-free ternary solar cells are fabricated based on a wide bandgap acceptor, IDTT-M, together with a wide bandgap donor polymer PM6 and a narrow bandgap NFA Y6. Insights from the morphological and electronic characterizations reveal that IDTT-M has been incorporated into Y6 domains without disrupting its molecular packing and sacrificing its electron mobility and work synergistically with Y6 to regulate the packing pattern of PM6, leading to enhanced hole mobility and suppressed recombination. IDTT-M further functions as an energy-level mediator that increases open-circuit voltage (V_OC) in ternary devices. In addition, efficient Förster resonance energy transfer (FRET) between IDTT-M and Y6 provides a non-radiative pathway for facilitating exciton dissociation and charge collection. As a result, the optimized ternary device features a significantly improved PCE up to 16.63% with simultaneously enhanced short-circuit current (J_SC), V_OC, and fill factor (FF).