lizhendong

A new molecularly engineered nonfullerene acceptor, 2,2′-(5,5′-(9,9-didecyl-9H-fluorene-2,7-diyl)bis(benzo[c][1,2,5]thiadiazole-7,4-diyl)bis(methanylylidene))bis(3-hexyl-1,4-oxothiazolidine-5,2-diylidene))dimalononitrile (BAF-4CN), with fluorene as the core and arms of dicyano-n-hexylrhodanine terminated benzothiadiazole is synthesized and used as an electron acceptor in bulk heterojunction organic solar cells. BAF-4CN shows a stronger and broader absorption with a high molar extinction coefficient of 7.8 × 10⁴m⁻¹ cm⁻¹ at the peak position (498 nm). In the thin film, the molecule shows a redshift around 17 nm. The photoluminescence experiments confirm the excellent electron accepting nature of BAF-4CN with a Stern–Volmer coefficient (K_sv) of 1.1 × 10⁵m⁻¹. From the electrochemical studies, the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels of BAF-4CN are estimated to be −5.71 and −3.55 eV, respectively, which is in good synchronization with low bandgap polymer donors. Using BAF-4CN as an electron acceptor in a poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3″′-di(2-octyldodecyl) 2,2′;5′,2″;5″,2″′-quaterthiophen-5,5″′-diyl)] based bulk-heterojunction solar cell, a maximum power conversion efficiency of 8.4% with short-circuit current values of 15.52 mA cm⁻², a fill factor of 70.7%, and external quantum efficiency of about 84% covering a broad range of wavelength is achieved.

The non-fullerene acceptor (NFA) BAF-4CN is synthesized for organic photovoltaic (OPV) application to overcome the drawbacks of fullerene. BAF-4CN shows stronger absorption compared to phenyl C₇₁-butyric acid methyl ester and has an excellent electron accepting nature and high charge carrier mobility. A power conversion efficiency of 8.4% is achieved from PffBT4T-2OD:BAF-4CN based bulk heterojunction solar cells. This may be a promising substitute for fullerene in low-cost solution-processed OPV.

On page 9204, thinness-controllable ultrathin perovskite wafers are prepared by Z. Yang, S. Z. (F.) Liu, and co-workers using a microreactor. Based on the single-crystalline perovskite wafer, high-performance photoresponse arrays are fabricated, demonstrating the feasibility of mass production of integrated circuits (ICs) on the perovskite wafer. It is envisioned that the present technique may provide an effective strategy for single-crystalline wafer preparation for demanding high-quality, low-cost device applications.

Five polymer donors with distinct chemical structures and different electronic properties are surveyed in a planar and narrow-bandgap fused-ring electron acceptor (IDIC)-based organic solar cells, which exhibit power conversion efficiencies of up to 11%.

A versatile metal nanowiring platform for producing individually controllable, large-scale, and long continuous silver nanowires (AgNWs) is demonstrated by T.-W. Lee and co-workers on page 9109, using polymer-assisted continuous and aligned metal-NW printing. One- and two-dimensional AgNW electrodes are successfully applied to various large-scale nano- and optoelectronic devices, including all-NW transistors composed of printed organic semiconducting and metal NWs.

Ternary polymer solar cells are fabricated based on one donor PBDB-T and two acceptors (a methyl-modified small-molecular acceptor (IT-M) and a bis-adduct of Bis[70]PCBM). A high power conversion efficiency of 12.2% can be achieved. The photovoltaic performance of the ternary polymer solar cells is not sensitive to the composition of the blend.

Selective unipolarization of an ambipolar polymer semiconductor, PNDTI-BT, by using different self-assembled monolayers, is demonstrated. For p-unipolarization, 1H,1H,2H,2H-perfluorodecyltriethoxysilane is most effective, whereas for n-unipolarization, 3-(N, N′-dimethylamino)propyltriethoxysilane is the best. Using these selective unipolarization effects, the complementary inverters based on the ambipolar polymer fabricated by a simple solution process show greatly improved switching behaviors with low power consumption.

Solution-processed hybrid perovskite semiconductors attract a great deal of attention, but little is known about their formation process. The one-step spin-coating process of perovskites is investigated in situ, revealing that thin-film formation is mediated by solid-state precursor solvates and their nature. The stability of these intermediate phases directly impacts the quality and reproducibility of thermally converted perovskite films and their photovoltaic performance.

Low-bandgap CH₃NH₃(Pb_xSn_1–x)I₃ (0 ≤ x ≤ 1) hybrid perovskites (e.g., ≈1.5–1.1 eV) demonstrating high surface coverage and superior optoelectronic properties are fabricated. State-of-the-art photovoltaic (PV) performance is reported with power conversion efficiencies approaching 10% in planar heterojunction architecture with small (<450 meV) energy loss compared to the bandgap and high (>100 cm² V⁻¹ s⁻¹) intrinsic carrier mobilities.

A low-temperature, solution-processable organic electron-transporting material (ETM) is successfully developed for efficient conventional n-i-p perovskite solar cells (PVSCs). This ETM can show a high efficiency over 17% on rigid device and 14.2% on flexible PVSC. To the best of our knowledge, this efficiency is among the highest values reported for flexible n-i-p PVSCs with negligible hysteresis thus far.

After the first report in 2008, diketopyrrolopyrrole (DPP)-based small-molecule photovoltaic materials have been intensively explored. The power conversion efficiencies (PCEs) for the DPP-based small-molecule donors have been improved up to 8%. Furthermore, through judicious structure modification, DPP-based small molecules can also be converted into electron-acceptor materials, and, recently, some exciting progress has been achieved. The development of DPP-based photovoltaic small molecules is summarized here, and the photovoltaic performance is discussed in relation to structural modifications, such as the variations of donor–acceptor building blocks, alkyl substitutions, and the type of conjugated bridges, as well as end-capped groups. It is expected that the discussion will provide a guideline in the exploration of novel and promising DPP-containing photovoltaic small molecules.

Diketopyrrolopyrrole (DPP)-based small-molecule photovoltaic materials are being intensively explored and can be divided into three types: single-DPP, double-DPP, and multi-DPP respectively. The recent progress regarding DPP-based photovoltaic small molecules is highlighted and the photovoltaic performance in relation to structural modification such as the variations of donor–acceptor building blocks, alkyl substitutions, the type of conjugated bridges, and the type of end-capped groups is discussed.

A general doping strategy, using a wide range of acids with different pK_a values as additive, is demonstrated to enhance the conductivity of spiro-OMeTAD, the dominant hole transport material in perovskite solar cells (PSCs). Hysteresis-less planar PSCs with ≈19% efficiency and better open-circuit voltage and fill factor is achieved with acid doped spiro-OMeTAD.

A synergetic effect of molecular weight (M_n) and fluorine (F) on the performance of all-polymer solar cells (all-PSCs) is comprehensively investigated by tuning the M_n of the acceptor polymer poly((N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl)-alt-5,5′-(2,2′-bithiophene)) (P(NDI2OD-T2)) and the F content of donor polymer poly(2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-dyl-alt-thiophene-2,5-diyl). Both M_n and F variations strongly influence the charge transport properties and morphology of the blend films, which have a significant impact on the photovoltaic performance of all-PSCs. In particular, the effectiveness of high M_n in increasing power conversion efficiency (PCE) can be greatly improved by the devices based on optimum F content, reaching a PCE of 7.31% from the best all-PSC combination. These findings enable us to further understand the working principles of all-PSCs with a view on achieving even higher power conversion efficiency in the future.

To establish a correlation between the effects of molecular weight (M_n) and fluorine (F) on photovoltaic performance, all-polymer solar cells have been comprehensively investigated based on donor polymers of TQ family with various F content and P(NDI2OD-T2) acceptor polymers with various M_n. An efficiency of 7.31% is demonstrated by blending the optimum F content-containing donor with a high M_n acceptor.

A charge carrier in a lead halide perovskite lattice is protected as a large polaron responsible for the remarkable photophysical properties, irrespective of the cation type. All-inorganic-based APbX₃ perovskites may mitigate the stability problem for their applications in solar cells and other optoelectronics.

Compositional modification and surface treatments of a TiO₂ film prepared by a low-temperature route are carried out by a new promising method. Inverted polymer solar cells incorporating the post-treated TiO₂:TOPD electron-transport layer achieve the highest efficiency of 10.5%, and more importantly, eliminate the light-soaking problem that is commonly observed in metal-oxide-based inverted polymer solar cells.

In article number 1600767, Antonio Abate and co-workers report a method to obtain a compact perovskite layer with larger grains, aiming for high performance perovskite solar cells with 19.5% power conversion efficiency. The image shows the mechanism of controlling perovskite crystal growth with ionic liquid, methylammonium formate (MAF). MAF can selectively interact with Pb, which can retard PbI₂-methylammonium iodide (MAI) interaction to form perovskite.

Thomas Wågberg, Ludvig Edman, and co-workers present in article number 1600738 an artificial-leaf device comprising lightweight electrocatalyst electrodes powered by solution-processed perovskite photovoltaics. The electrocatalyst, comprising NiCo₂O₄ nanorods anchored onto carbon paper via nitrogen-doped carbon nanotubes, operates efficiently as both anode and cathode in alkaline solution. The wired artificial leaf can be very low cost and features a solar-to-hydrogen efficiency of 6.2%.