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Efficient electron transport layer–free perovskite solar cells (ETL‐free PSCs) with cost‐effective and simplified design can greatly promote the large area flexible application of PSCs. However, the absence of ETL usually leads to the mismatched indium tin oxide (ITO)/perovskite interface energy levels, which limits charge transfer and collection, and results in severe energy loss and poor device performance. To address this, a polar nonconjugated small‐molecule modifier is introduced to lower the work function of ITO and optimize interface energy level alignment by virtue of an inherent dipole, as verified by photoemission spectroscopy and Kelvin probe force microscopy measurements. The resultant barrier‐free ITO/perovskite contact favors efficient charge transfer and suppresses nonradiative recombination, endowing the device with enhanced open circuit voltage, short circuit current density, and fill factor, simultaneously. Accordingly, power conversion efficiency increases greatly from 12.81% to a record breaking 20.55%, comparable to state‐of‐the‐art PSCs with a sophisticated ETL. Also, the stability is enhanced with decreased hysteresis effect due to interface defect passivation and inhibited interface charge accumulation. This work facilitates the further development of highly efficient, flexible, and recyclable ETL‐free PSCs with simplified design and low cost by interface electronic structure engineering through facile electrode modification. A polar nonconjugated small molecule ultrathin layer with an intrinsic dipole moment is introduced to modify the work function of indium tin oxide and to optimize the front interface energy level alignment, which contributes to suppressed energy loss and results in a 20.55% efficient electron transport layer–free perovskite solar cell with enhanced open‐circuit voltage short circuit current density and fill factor, simultaneously.

In recent decades, the demand for clean and renewable energy has grown increasingly urgent due to the irreversible alteration of the global climate change. As a result, organic solar cells (OSCs) have emerged as a promising alternative to address this issue. In this review, we summarize the recent progress in the molecular design strategies of benzodithiophene (BDT)‐based polymer and small molecule donor materials since their birth, focusing on the development of main‐chain engineering, side‐chain engineering and other unique molecular design paths. Up to now, the state‐of‐the‐art power conversion efficiency (PCE) of binary OSCs prepared by BDT‐based donor materials has approached 20%. This work discusses the potential relationship between the molecular changes of donor materials and photoelectric performance in corresponding OSC devices in detail, thereby presenting a rational molecular design guidance for stable and efficient donor materials in future. This summary diagram comprehensively and reasonably reviews the evolution of BDT‐based donor materials over the last 20 years by subdividing the molecular design strategies of main‐chain engineering, side‐chain engineering as well as other engineering based on the detailed molecular structure of BDT‐based polymer donors and small molecule donors.

Photovoltaic conversion of solar energy into electricity is an alternative way to use renewable energy for sustainable energy production. The great demand of low-cost and efficient solar cells inspires research on solution-processable light-harvesting materials. Antimony trisulfide (Sb 2 S 3 ) is a promising light-harvester for photovoltaic purposes. Here we report on the in situ grown monolayer of preferentially oriented, large Sb 2 S 3 single-crystalline cuboids on a polycrystalline titania (TiO 2 ) nanoparticle film. A facile, oriented seed-assisted solution-processing method is used, providing the Sb 2 S 3 /TiO 2 -based bulk/nano-planar heterojunction with a preferred structure for efficient planar solar cells. An orientation-competing-epitaxial nucleation/growth mechanism is proposed for understanding the growth of the Sb 2 S 3 single-crystalline cuboids. With an organic hole transporting material, the stable solar cell of the heterojunction yields a power conversion efficiency of 5.15% (certified as 5.12%). It is found that the [221]-oriented Sb 2 S 3 cuboids provide highly effective charge transport channels inside the Sb 2 S 3 layer. Antimony trisulfide is a promising light harvester for photovoltaics. Here the growth of single-crystals of antimony trisulfide on polycrystalline titania is reported to proceed via an epitaxial nucleation/growth mechanism. The resulting solar cell delivers a power conversion efficiency of 5.12%.

Small molecules improve the characteristics of polymer solar cells. 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%.

A novel route is presented for preparation of poly(1-methoxy-4-(2-ethylhexyloxy)- p -phenylenevinylene) (MEH-PPV)-functionalized TiO 2 nanoparticles (NPs), resulting in a hybrid nanocomposite (MEH-PPV~TiO 2 NPs). Thermogravimetric analysis (TGA) was used to evaluate the exact content of TiO 2 nanoparticles in the MEH-PPV~TiO 2 nanocomposites. Fourier-transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), and photophysical properties showed that the conjugated polymer chains intimately contact with the inorganic semiconductors. The performance of photovoltaic devices based on the MEH-PPV~TiO 2 NPs nanocomposite was investigated by current–voltage ( J – V ) characteristics and intensity-modulated photovoltage spectroscopy (IMVS). Device performance was greatly improved by direct application of MEH-PPV~TiO 2 NPs nanocomposites as the active layer as compared with devices with simply blended counterparts (MEH-PPV/TiO 2 NPs). In addition, IMVS revealed that the longer electron lifetime was accompanied by higher open-circuit voltage in the MEH-PPV~TiO 2 NPs devices.

With the generation of Y6, organic solar cells have reached remarkable achievement of over 19% efficiency. Alkyl chain is of importance to modulate intermolecular stacking and possibly enhance optoelectronic properties of small molecule acceptors (SMAs). Three alkyl chains of 2-ethylhexyl, 2-butylocyl and 3-ethylheptyl were selected to obtain G6-EH, G6-BO and G6-EHep molecules, respectively. Compared to G6-EH and G6-BO, G6-EHep was found inducing unfavourable large domain size. Furthermore, we discover that 2-butyloctyl effectively inhibits monomolecular and bimolecular recombination, improves molecular packing, generates more balanced carrier mobility and enhances exciton dissociation. The SMA with 2-butyloctyl alkyl chains (G6-BO) shows the best electrical and morphological characteristics, achieving a higher power conversion efficiency (PCE) of 17.06%, with an open circuit voltage of 0.912 V, a short-circuit current of 24.22 mA cm −2 and a fill factor of 77.25%. Finally, using the ternary strategy by incorporating the G6-BO acceptor into PM6:BTP-eC9, we achieved a higher PCE of 18.13% with enhanced electron transport.

Highly conductive poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonic acid) (PEDOT:PSS) has been explored to fabricate flexible and stretchable conductors. Generally, PEDOT:PSS transparent anodes are prepared by spin-coating method. In this article, we adopt a method by dropping PEDOT:PSS aqueous solution on the PET plastic substrate to fabricate flexible electrodes. Compared with spin coating, drop-coating is simple and cost-effective with large-area fabrications. Through this method, we fabricated highly transparent conductive electrodes and systematically studied their electrical, optical, morphological and mechanical properties. With dimethyl sulfoxide/methanesulfonic acid (DMSO/MSA) treated PEDOT:PSS electrode, bendable devices based on non-fullerene system displayed an open-circuit voltage of 0.925 V, a fill factor of 70.74%, and a high power conversion efficiency (PCE) of 10.23% under 100 mW cm −2 illumination, which retained over 80% of the initial PCE value after 1000 bending cycles. Based on the findings, drop-coated PEDOT:PSS electrodes exhibited high suitability for the development of large-area and high-efficiency printed solar cell modules in the future.

Ternary organic solar cells (OSCs) have received extensive attention for improving the power conversion efficiency (PCE) of organic photovoltaics (OPVs). In this work, a novel donor material (ECTBD) consisting of benzodithiophene (BDT) central electron donor unit was developed and synthesized. The small molecular donor has the same central unit as PM6. The addition of ECTBD into PM6:Y6 system could improve the morphology of active blend layer. In addition, ECTBD showed good morphologically compatibility when blending with PM6:Y6 host, resulting in the improvement of fill factor and current density. As a result, the ternary devices based on PM6:ECTBD:Y6 ternary system achieved a highest PCE of 16.51% with fill factor of 76.24%, which was much higher than that of the binary devices (15.7%). Overall, this work provided an effective strategy to fabricate highly efficient ternary organic solar cells through design of the novel small molecular donor as the third component.

A new conjugated polymer PPV-PCN containing alternating alkoxy-substituted aromatic and cyano-substituted aromatic units was synthesized and characterized by NMR, FIR, GPC and TGA. The UV–vis absorption spectra and photoluminescence emission spectra in solution/films were characterized. The results indicate PPV-PCN has a smaller optical band gap value (2.05 eV) compared to homopolymer MEH-PPV, it is ascribed to PPV-PCN with structure of alternative electron-rich alkoxy substituted aromatic and electron-deficient cyano group along conjugated backbone. Its photoinduced charge transfer application in trinitrotoluene (TNT) detection was studied, and the results show that this polymer can be a potential material for detecting TNT in solution. Two types of cells, including inverted-type and conventional-type were studied for PSCs application as well, and the results indicate that the inverted-type device demonstrates better long-term ambient stability as compared to the conventional device and achieves 0.91 % power conversion efficiency finally