as PM6 [13,14] and PBDB-T [15] with narrow bandgap nonfullerene acceptors (A), for example, IT-4F, [14] and Y6 [8] has remained as a wise strategy to absorb solar irradiation in the range of 500-900 nm or even up to a broader absorption region. However, solar irradiation in the spectrum range of 300-500 nm remains unabsorbed. The construction of ternary device by introducing a third component into the photoactive layer has been proven to overcome this issue effectively, where full utilization of solar irradiation in the entire solar spectrum can be realized without complicating the traditional fabrication processes. [16][17][18][19][20][21][22][23] Fullerene derivatives like phenyl-C71-butyric-acid-methyl ester (PC 71 BM) with the main absorption in the range of 300-500 nm have been commonly used as a third component to strengthen the light-harvesting capability of active layers, thus providing a potential route to enhance the short-circuit current density (J sc ) and PCE. [24] Some recent theoretical models and mechanisms have been proposed to provide guide and reference for future development of ternary devices. [25][26][27] Among them, three models which include charge transfer model, [17] energy transfer model, [28] and parallel-like or alloy-like model [16,29] have been widely accepted. In the charge transfer model, the third component in the active layer participates in the process of exciton dissociation and charge carrier generation in the donor/ acceptor interface. [22,30] A cascaded energy level distribution is the requirement for such mechanisms to take place. [31] In contrast, in the energy transfer model, the third component serves as an "energy donor" which absorbs additional solar energy and delivers it to donor or acceptor by Förster or Dexter energy transfer. [32] Ternary devices based on charge transfer or energy transfer mechanisms improve J sc by utilizing additional solar energy. [33,34] Ternary devices based on charge transfer mechanism will affect the open-circuit voltage (V oc ) while the devices based on energy transfer mechanism can hardly impact the V oc due to their roles in charge transfer and dissociation. [35] The third one is the parallel-like or alloy-like model, of which the mechanism does not require any certain energy levels.In parallel-like model, the third component serves as a donor (or acceptor) and work independently with another donor (or acceptor). [36] The ternary device can be viewed as two subcells that are mixed together. For the alloy-like model, the third component is finely mixed with one of the host components to form a two-phase morphology. In this process, dual donors Ternary heterojunction strategies appear to be an efficient approach to improve the efficiency of organic solar cells (OSCs) through harvesting more sunlight. Ternary OSCs are fabricated by employing wide bandgap polymer donor (PM6), narrow bandgap nonfullerene acceptor (Y6), and PC 71 BM as the third component to tune the light absorption and morphologies of the blend films. A record power conver...

Polymer solar cells have drawn a great deal of attention due to the attractiveness of their use in renewable energy sources that are potentially lightweight and low in cost. Recently, numerous significant research efforts have resulted in polymer solar cells with power conversion efficiencies in excess of 9% (ref. 1). Nevertheless, further improvements in performance are sought for commercial applications. Here, we report polymer solar cells with a power conversion efficiency of 10.02% that employ a non-conjugated small-molecule electrolyte as an interlayer. The material offers good contact for photogenerated charge carrier collection and allows optimum photon harvesting in the device. Furthermore, the enhanced performance is attributed to improved electron mobility, enhanced active-layer absorption and properly active-layer microstructures with optimal horizontal phase separation and vertical phase gradation. Our discovery opens a new avenue for single-junction devices by fully exploiting the potential of various material systems with efficiency over 10%.In recent decades, polymer solar cells (PSCs) based on conjugated polymers as donors (D) blended with fullerene derivatives as acceptors (A) have received an enormous amount of attention in renewable energy sources because of the promise of low cost, flexibility and large-area fabrication 2-5 . To date, the best reported power conversion efficiency (PCE) in PSCs is ∼9-10%, but most values remain below 10%, especially in single-junction PSCs 6-11 . It is therefore highly desirable to develop novel materials and devices for the creation of single-junction PSCs with excellent efficiencies.To achieve such high efficiencies, energy loss in PSCs should be minimized. In general, energy loss originates directly from the reflection, transmission, exciton recombination and exciton annihilation of active and/or interface layers, as well as the accumulation on electrodes. The key is therefore to develop suitable materials for active and interfacial layers that can significantly reduce the loss of energy. For active-layer materials, considerable progress has been demonstrated with broadband absorption and high carrier mobility, resulting in state-of-the-art single-junction PSCs with PCEs up to ∼10% 12,13 . Meanwhile, triple-junction tandem devices have also been developed that achieve a high PCE of 11.5%, by combining different high-performance active-layer materials [14][15][16] . Before the studies on active-layer materials and devices, the interlayer between the cathode and active layer was also thought to be an important factor in the realization of highly efficient PSCs by avoiding the accumulation of excitons. The selection of proper electrodes with matched workfunctions is an effective method to reduce this accumulation and improve efficiency. However, the availability of suitable electrodes is limited for the emerging active-layer materials of different energy levels, so some investigators have suggested using an interfacial layer between the active layer and electro...

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All-solution-processing at low temperatures is important and desirable for making printed photovoltaic devices and also offers the possibility of a safe and cost-effective fabrication environment for the devices. Herein, an all-solution-processed flexible organic solar cell (OSC) using poly(3,4-ethylenedioxythiophene):poly-(styrenesulfonate) electrodes is reported. The all-solution-processed flexible devices yield the highest power conversion efficiency of 10.12% with high fill factor of over 70%, which is the highest value for metal-oxide-free flexible OSCs reported so far. The enhanced performance is attributed to the newly developed gentle acid treatment at room temperature that enables a high-performance PEDOT:PSS/plastic underlying substrate with a matched work function (≈4.91 eV), and the interface engineering that endows the devices with better interface contacts and improved hole mobility. Furthermore, the flexible devices exhibit an excellent mechanical flexibility, as indicated by a high retention (≈94%) of the initial efficiency after 1000 bending cycles. This work provides a simple route to fabricate high-performance all-solution-processed flexible OSCs, which is important for the development of printing, blading, and roll-to-roll technologies.

Non‐fullerene all‐small‐molecule organic solar cells (NFSM‐OSCs) have shown potential as OSCs, owing to their high purity, easy synthesis and good reproducibility. However, challenges in the modulation of phase separation morphology have limited their development. Herein, two novel small molecular donors, BTEC‐1F and BTEC‐2F, derived from the small molecule DCAO3TBDTT, are synthesized. Using Y6 as the acceptor, devices based on non‐fluorinated DCAO3TBDTT showed an open circuit voltage (Voc) of 0.804 V and a power conversion efficiency (PCE) of 10.64 %. Mono‐fluorinated BTEC‐1F showed an increased Voc of 0.870 V and a PCE of 11.33 %. The fill factor (FF) of di‐fluorinated BTEC‐2F‐based NFSM‐OSC was improved to 72.35 % resulting in a PCE of 13.34 %, which is higher than that of BTEC‐1F (61.35 %) and DCAO3TBDTT (60.95 %). To our knowledge, this is the highest PCE for NFSM‐OSCs. BTEC‐2F had a more compact molecular stacking and a lower crystallinity which enhanced phase separation and carrier transport.

Organic emitters play a vital role in determining the overall performance of organic light emitting diode (OLED) devices. Traditional fluorescent emitters can only achieve external quantum efficiency (EQE) of 5%, far below expectation; therefore many efforts have been spent on increasing the EQE of OLEDs. Phosphorescence, thermally activated delayed fluorescence, triplet–triplet annihilation, and hybridized local and charge transfer are the most widely applied approaches to harvest the 75% triplet excitons for luminescence. As for selecting or designing suitable emitters for practical applications, it is strongly demanded to have an overall view about emitters of high exciton utilizing efficiency (EUE) from molecule level, i.e., the four common approaches mentioned above and some latest ones of the doublet, singlet fission, triplet–polar annihilation, and rotationally accessed spin state inversion, and also from the aggregated state such as aggregation‐induced emission. In this review, the current progress of highly efficient emitters is presented, covering the chemical structures, the high‐EUE mechanisms in molecule level and aggregated state, and their applications in OLED devices. This review hopefully will illustrate highly efficient electroluminescent materials and their mechanisms, but more importantly, provide helpful information on how to design or select suitable emitters for specific OLED devices.

This paper describes a solvothermal approach to synthesize CuInS2 quantum dots (QDs) and demonstrates their application as a potential electron accepting material for polymer-based hybrid solar cells, for the first time. The CuInS2 QDs with a size of 2-4 nm are synthesized by the solvothermal method with 4-bromothiophenol (HSPh) as both reduction and capping agents, and characterized by XRD, XPS, TEM, FT-IR, cyclic voltammetry (CV), and absorption and photoluminescence spectra. Results reveal that the CuInS2 QDs result from the solvothermal decomposition of a soluble organic sodium salt as an intermediate precursor formed by simple reactions among CuCl2, InCl3, HSPh and Na2S at room temperature; they have an ionization potential (IP) of -5.8 eV and an electron affinity (EA) of -4.0 eV and can quench effectively the luminescence of poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV). Due to the favorable IP and EA positions with respect to MEH-PPV, the CuInS2 QDs act as an effective electron acceptor for the hybrid solar cells based on MEH-PPV/CuInS2-QDs blends with a wide spectral response extending from 300 to 900 nm, by allowing the efficient charge separation for neutral excited states produced either on the polymer or on the QDs. The MEH-PPV/CuInS2-QDs solar cells exhibit a promising open circuit voltage (V-oc) of 0.62 V under the monochromic illumination of 15.85 mW cm(-2) at 470 nm. The charge transfer processes in the solar cells are also described

solution-processability, and lightweight property. [1][2][3][4][5][6] Recently, the power conversion efficiency (PCE) of a single-junction device based on binary photoactive layer system had surpassed the 15-16% boundaries for opaque OSCs and 11-12% boundaries for semitransparent OSCs (ST-OSCs), all of which were fabricated on rigid glass substrates. [7][8][9][10][11][12][13][14] Though the PCE had increased remarkably on rigid glass substrates, development of OSCs on flexible substrates particularly for flexible ST-OSCs still lagged behind. [15][16][17][18] To date, the highest reported PCE for flexible ST-OSCs with average visible light transmittance (AVT) of over 20% was just over 10%. [19] Greater attentions should be focused on the development of flexible ST-OSCs due to its promising potentials as power-generating windows/roofs in building-integrated photovoltaics and photovoltaic vehicles. Additionally, one needs to consider the foldability properties of flexible ST-OSCs if advanced applications in 3D curved surfaces (e.g., future foldable roofs in multifunctional selfpowered greenhouse) are to be realized. This situation drove the current works for foldable-flexible ST-OSCs (hereafter referred to as FST-OSCs).Over the years, studies on ST-OSCs and/or FST-OSCs have centered around materials design of the photoactive layer (design of novel donor/acceptor). [6,20,21] Generally, photo active layer is designed to readily absorb solar irradiation in the nearinfrared (NIR) to infrared (IR) region while being partially transparent in the visible light region. These IR-absorbing photoactive layers are particularly favorable for agricultural applications (e.g., common greenhouse) as sunlight in the visible light region can be predominantly transmitted for plants growth. In fact, solar irradiation located in the visible light region (370-740 nm) is mostly responsible for photosynthesis processes in plants for growth. [22] Through this, ST-OSCs and/ or FST-OSCs for photovoltaic and photosynthesis can be realized, proving the future potential of semitransparent devices as windows/roofs in multifunctional self-powered greenhouse.FST-OSCs have several key parameters similar to its rigid counterparts, such as efficiency, transparency, color, and color rendering property. The main distinct feature of FST-OSCs is its mechanical stability against extreme mechanical Semitransparent organic solar cells (ST-OSCs) have attracted extensive attention for their potential greenhouse applications. Conventional ST-OSCs are typically based on indium tin oxide (ITO) electrodes which suffer from mechanical brittleness. Therefore, alternatives for ITO are required for realization of foldable-flexible ST-OSCs (FST-OSCs). Herein, flexible poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) electrodes are prepared as ITO alternatives via polyhydroxy compound (xylitol) microdoping and acid treatment. As a result, flexible opaque OSCs based on PBDB-T-2F:Y6 photoactive system yield a high efficiency of 14.20%. The desirable optic...