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Benefiting from the synergistic development of material design, device engineering, and the mechanistic understanding of device physics, the certified power conversion efficiencies (PCEs) of single‐junction non‐fullerene organic solar cells (OSCs) have already reached a very high value of exceeding 19%. However, in addition to PCEs, the poor stability is now a challenging obstacle for commercial applications of organic photovoltaics (OPVs). Herein, recent progress made in exploring operational mechanisms, anomalous photoelectric behaviors, and improving long‐term stability in non‐fullerene OSCs are highlighted from a novel and previously largely undiscussed perspective of engineering exciton and charge carrier pathways. Considering the intrinsic connection among multiple temporal‐scale photocarrier dynamics, multi‐length scale morphologies, and photovoltaic performance in OPVs, this review delineates and establishes a comprehensive and in‐depth property‐function relationship for evaluating the actual device stability. Moreover, this review has also provided some valuable photophysical insights into employing the advanced characterization techniques such as transient absorption spectroscopy and time‐resolved fluorescence imagings. Finally, some of the remaining major challenges related to this topic are proposed toward the further advances of enhancing long‐term operational stability in non‐fullerene OSCs. [ABSTRACT FROM AUTHOR]

Accurate determination of charge carrier density in organic solar cells under light irradiation is essential because charge carrier density is directly related to the bimolecular recombination rate and open-circuit voltage of the cells. We investigate the robustness of transient photovoltage/current (TPV/C) and impedance spectroscopy (IS) to interference from the geometric capacitance of the cells (Cgeo) during quantification of the charge carrier density. TPV/C and IS accurately quantify the charge carrier density of bulk heterojunction cells with small Cgeo. For planar heterojunction cells with a larger Cgeo contribution, IS fails to separate the charge carriers in the organic layer from those in the electrodes. In contrast, TPV/C eliminates the effect of Cgeo and gives a reasonable estimation of the charge carrier density in the organic layer with the planar heterojunction, demonstrating that TPV/C is more robust than IS to interference from Cgeo of the cells. [ABSTRACT FROM AUTHOR]

Abstract: To maximize the short‐circuit current density (JSC) and the open circuit voltage (VOC) simultaneously is a highly important but challenging issue in organic solar cells (OSCs). In this study, a benzotriazole‐based p‐type polymer (J61) and three benzotriazole‐based nonfullerene small molecule acceptors (BTA1‐3) are chosen to investigate the energetic driving force for the efficient charge transfer. The lowest unoccupied molecular orbital (LUMO) energy levels of small molecule acceptors can be fine‐tuned by modifying the end‐capping units, leading to high VOC (1.15–1.30 V) of OSCs. Particularly, the LUMO energy level of BTA3 satisfies the criteria for efficient charge generation, which results in a high VOC of 1.15 V, nearly 65% external quantum efficiency, and a high power conversion efficiency (PCE) of 8.25%. This is one of the highest VOC in the high‐performance OSCs reported to date. The results imply that it is promising to achieve both high JSC and VOC to realize high PCE with the carefully designed nonfullerene acceptors. [ABSTRACT FROM AUTHOR]

Organic solar cells (OSCs) are promising low-cost devices for generating electricity. In addition to fill factor, the short circuit current density ( JSC) and the open circuit voltage ( VOC) are two key factors that have critical influence on the device performance. The energy levels of the donor and acceptor materials are crucial for achieving a high JSC and VOC. However, the interfacial structures between the organic materials substantially affect the JSC and VOC through the energy of the charge transfer (CT) states and the charge separation and recombination reaction kinetics. Here, it is reported that separating the donor and acceptor layer in bilayer OSCs with a thin insulating layer increases the energy of the CT state by weakening the Coulomb interaction at the interface and this also suppresses photoinduced CT and recombination. Although these effects usually increase VOC and decrease JSC, the trade-off is avoided by doping the insulating layer with a dye to utilize the energy transfer process. The increase in VOC without the reduction in JSC enhances the conversion efficiency of the OSCs by 30%. [ABSTRACT FROM AUTHOR]

Low band gap dyad molecules were prepared that have absorption spectra matched well with the solar spectrum, and the construction of efficient charge transport pathways was observed. Under AM 1.5 illumination, the devices have achieved the highest JSC(4.79 mA cm2) and FF (0.46) in dyad-based organic solar cells to date. [ABSTRACT FROM AUTHOR]

A fullerene attached all-semiconducting polymer was synthesized and applied to single component polymer photovoltaic cells. The current approach gives a method of obtaining a reliable donor acceptor mixing morphology by molecular design and achieving efficient photovoltaic devices with long thermal stability. [ABSTRACT FROM AUTHOR]

novel oligo(p-phenylenevinylene) (OPV)-fullerene dyad, with strong intermolecular π-π interactions between the donor groups, led to improvements in the fill factor and power conversion efficiency of dyad-based solar cells of up to 0.44 and 1.28%, respectively, which are the highest values reported for dyad-based solar cells to date. [ABSTRACT FROM AUTHOR]

Naphthalene diimide (NDI) and dithienosilole (DTS) have been well known building blocks for photovoltaic materials. Herein a solution-processable low band gap conjugated polymer, PDTS-NDI, consisting of NDI moiety and DTS unit was synthesized as a new n-type material. The polymer has two broad absorption bands in the range of 300–500 nm and 500–950 nm. Power conversion efficiencies (PCEs) of the polymer blend solar cells in the range of 0.13–0.70% were obtained under simulated AM 1.5, 100 mW/cm 2 irradiation, where two polymers with conjugated side chains, PT1 and TTV2, were used as p-type material. For the combination of TTV2 and PDTS-NDI, it was further optimized to give a PCE of 1.19% by adding 1,8-diiodooctane (DIO) as solvent additive, suggesting a potential of PDTS-NDI polymer for the photovoltaic application. [ABSTRACT FROM AUTHOR]

Abstract: To pursue high power conversion efficiency (PCE) of polymer solar cells (PSCs), many new semiconducting polymers with low band gaps have been developed in the past several years. In this perspective paper, we focused on super low band gap photovoltaic polymers with photocurrent response extending over 1000nm. This kind of micrometer-response polymers (μmR-polymer) could increase the short circuit current (J SC) due to better match of absorption spectra of the polymers with the solar irradiation and show tremendous potential for application in tandem solar cells and transparent solar cells. The necessary conditions for the design of this kind of μmR-polymers are discussed. Furthermore, the remaining problems and challenges, and the key research direction in near future are discussed. [Copyright &y& Elsevier]

Abstract: Four 9-cyanomethylenefluorene derivatives were synthesized as a new class of electron-deficient building blocks for donor–acceptor (D–A) type alternating copolymers. UV–vis absorption spectroscopy, cyclic voltammetry and density functional theory calculations show that the substituent X at the cyanomethylene unit, depending on its electron-withdrawing ability (X=–H, –CONMe2, –COOiBu and –CN), can continuously control the LUMO energy level of the monomer. D–A type copolymers were synthesized using the derivatives and an oligothiophene as the electron-donating block. The photovoltaic performance of D–A copolymer:PCBM bulk heterojunction devices shows the importance of LUMO level alignment to achieve efficient charge separation at the donor/acceptor interface. After optimization, the power conversion efficiency of the device with X=–H reached 1.14% with V OC of 0.61V, J SC of 3.24mAcm−2 and FF of 0.58 under the irradiation of AM1.5 simulated solar light. The electronic properties of the copolymers correlated well with the electron-withdrawing ability of the monomers while the structure of the π-conjugated backbone was preserved, demonstrating the advantage of the chemically tunable monomer design. [Copyright &y& Elsevier]

Abstract: Use of a lamination process for the introduction of Au electrode, instead of conventional metal evaporation, improved the power conversion efficiency (PCE) of inverted-structure photovoltaic devices from 1.6% to 2.6% based on a bulk heterojunction of poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl C61 butyric acid methyl ester (PCBM). X-ray photoelectron spectroscopy indicated that a thin layer of P3HT is spontaneously formed at the air/polymer blend layer interface during the spin-coating process. It is suggested that the vacuum-evaporated gold could destroy the surface-segregated thin layer of P3HT, while the lamination process preserves the surface structure working as an electron-blocking layer. The insertion of a PEDOT:PSS layer, between the metal electrode and polymer layer, in the lamination process further improved the PCE to 3.3% with a short-circuit current density of 9.94mAcm−2, an open-circuit voltage of 0.60V, and a fill factor of 55% under AM1.5 100mWcm−2 irradiation. [Copyright &y& Elsevier]

A novel semiconducting polymer poly(4-hexyloxythiazole) with a low optical band gap of 1.4 eV was synthesized and used in organic electronic devices. X-ray diffraction (XRD) measurements reveal a high degree of crystallinity and lamellar packing of poly(4-hexyloxythiazole) in the film similar to poly(3-hexylthiophene). Field effect transistor charge mobility of poly(4-hexyloxythiazole) arrived 0.02 cm 2 /V s. Bulk heterojunction type solar cells based on poly(4-hexyloxythiazole) shows a photoresponse up to about 900 nm. [ABSTRACT FROM AUTHOR]

A novel alternating copolymer with a low band gap (Eg= 1.55 eV), PBDT–DTBSe, based on benzodithiophene(BDT) and benzoselenadiazole (BSe) units with thiophene as a π-conjugatedbridge, was synthesized and characterized. When 1,8-diiodooctane wasused as a solvent additive to optimize the mixing morphology, themaximum power conversion efficiency reached by a polymer solar cellbased on PBDT–DTBSe/PC70BM was 5.18%, which wasslightly higher than that of the benzothiadiazole (BT)-based analogue(5.01%). These results demonstrated the promising effectiveness ofbenzoselenadiazole as an electron-deficient unit for the design ofthe donor–acceptor photovoltaic polymers. [ABSTRACT FROM AUTHOR]