ZiQi Sun

In addition to a good perovskite light absorbing layer, the hole and electron transport layers play a crucial role in achieving high-efficiency perovskite solar cells. Here, a simple, one-step, solution-based method is introduced for fabricating high quality indium-doped titanium oxide electron transport layers. It is shown that indium-doping improves both the conductivity of the transport layer and the band alignment at the ETL/perovskite interface compared to pure TiO₂, boosting the fill-factor and voltage of perovskite cells. Using the optimized transport layers, a high steady-state efficiency of 17.9% for CH₃NH₃PbI₃-based cells and 19.3% for Cs_0.05(MA_0.17FA_0.83)_0.95Pb(I_0.83Br_0.17)₃-based cells is demonstrated, corresponding to absolute efficiency gains of 4.4% and 1.2% respectively compared to TiO₂-based control cells. In addition, a steady-state efficiency of 16.6% for a semi-transparent cell is reported and it is used to achieve a four-terminal perovskite-silicon tandem cell with a steady-state efficiency of 24.5%.

Solution-processed, indium-doped TiO_x films are shown to be very effective electron transport/hole-blocking layers for high-performance perovskite cells. Doping improves the conductivity and work-function energy alignment at the ETL/perovskite interface, leading to high fill-factor and open-circuit voltage. An efficiency of ≈19.3% is demonstrated for a perovskite cell, and a steady-state efficiency of 24.5% is presented for a four-terminal perovskite-silicon tandem cell.

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.

Judicious choice of transport layer in organic–inorganic halide perovskite solar cells can be one of the essential parameters in photovoltaic design and fabrication techniques. This article reports the effect of optically generated dipoles in transport layer on the photovoltaic actions in active layer in perovskite solar cells with the architecture of indium tin oxide (ITO)/TiO _x /CH₃NH₃PbI_3–x Cl _x /hole transport layer (HTL)/Au. Here, PTB7-thieno[3,4-b]thiophene-alt-benzodithiophene and P3HT-poly(3-hexylthiophene) are separately used as the HTL with significant and negligible photoinduced dipoles, respectively. Electric field-induced photoluminescence quenching provides the first-hand evidence to indicate that the photoinduced dipoles are partially aligned in the amorphous PTB7 layer under the influence of device built-in field. By monitoring the recombination process through magneto-photocurrent measurements under device operation condition, it is shown that the photoinduced dipoles in PTB7 layer can decrease the recombination of photogenerated carriers in the active layer in perovskite solar cells. Furthermore, the capacitance measurements suggest that the photoinduced dipoles in PTB7 can decrease charge accumulation at the electrode interface. Therefore, the studies indicate the important role of photoinduced dipoles in the HTL on charge recombination dynamics and provide a fundamental insight on how the polarization in transport layer can influence the device performance in perovskite solar cells.

The influence of optically generated dipoles is reported in the hole transport layer of PTB7 on charge recombination dynamics occurring at active layer in perovskite solar cells. By monitoring the recombination of photogenerated carriers through magneto-photocurrent measurements, it is shown that photoinduced dipoles in PTB7 layer lead to less recombination and more dissociation in perovskite solar cells under device-operation condition.

The perovskite quantum dots are usually synthesized by solution chemistry and then fabricated into film for device application with some extra process. Here it is reported for the first time to in situ formation of a crosslinked 2D/3D NH₃C₄H₉COO(CH₃NH₃) _nPb_nBr_3n perovskite planar films with controllable quantum confine via bifunctional amino acid crosslinkage, which is comparable to the solution chemistry synthesized CH₃NH₃PbBr₃ quantum dots. These atomic layer controllable perovskite films are facilely fabricated and tuned by addition of bi-functional 5-aminovaleric acid (Ava) of NH₂C₄H₉COOH into regular (CH₃NH₃)PbBr₃ (MAPbBr₃) perovskite precursor solutions. Both the NH₃⁺ and the COO⁻ groups of the zwitterionic amino acid are proposed to crosslink the atomic layer MAPbBr₃ units via PbCOO bond and ion bond between NH₃⁺ and [PbX₆] unit. The characterizations by atomic force microscopy, scanning electron microscopy, Raman, and photoluminescence spectroscopy confirm a successful fabrication of ultrasmooth and stable film with tunable optical properties. The bifunctional crosslinked 2D/3D Ava(MAPbBr₃)_n perovskite films with controllable quantum confine would serve as distinct and promising materials for optical and optoelectronic applications.

A novel one-step in situ formation of crosslinked 2D/3D NH₃C₄H₉COO(CH₃NH₃PbBr₃)_n perovskite planar films with controllable quantum confines is reported, which is comparable to solution chemistry synthesized perovskite quantum dots. The zwitterionic amino acid NH₂C₄H₉COOH (Ava) in the CH₃NH₃PbBr₃ precursor can crosslink the atomic layer (CH₃NH₃PbBr₃)_n units by amino acids NH₃⁺ and the COO⁻ groups.

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.

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.

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.

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%.

Cesium lead halide quantum dots (QDs) have tunable photoluminescence that is capable of covering the entire visible spectrum and have high quantum yields, which make them a new fluorescent materials for various applications. Here, the synthesis of CsPbX₃ (X = Cl, Br, I, or mixed Cl/Br and Br/I) QDs by direct ion reactions in ether solvents is reported, and for the first time the synergetic effects of solvent polarity and reaction temperature on the nucleation and growth of QDs are demonstrated. The use of solvent with a low polarity enables controlled growth of QDs, which facilitates the synthesis of high-quality CsPbX₃ QDs with broadly tunable luminescence, narrow emission width, and high quantum yield. A QD white LED (WLED) is demonstrated by coating the highly fluorescent green-emissive CsPbBr₃ QDs together with red phosphors on a blue InGaN chip, which presents excellent warm white light emission with a high rendering index of 93.2 and color temperature of 5447 K, suggesting the potential applications of highly fluorescent cesium lead halide perovskite QDs as an alternative color converter in the fabrication of WLEDs.

CsPbX₃ quantum dots (QDs) have superior photophysics properties, including high quantum yield (up to 72%), wide color gamut (>NTSC standard), and narrow emission width (18–38 nm). The WLED based on CsPbBr₃ QDs present excellent warm white light emission with a high rendering index of 93.2 and CIE coordinate of (0.3339, 0.3617).

Hybrid perovskite and all-inorganic perovskite have attracted much attention in recent years owing to their successful use in the photovoltaic field. Usually the perovskite is used in its bulk form, although recently, perovskites' nanocrystalline form has received increased attention. Recent developments in the evolving research field of nanomaterial-based perovskite are reviewed. Both hybrid organic-inorganic and all-inorganic perovskite nanostructures are discussed, as well as approaches to tune the optical properties by controlling the size and shape of perovskite nanostructures. In addition, chemical modifications can change the perovskite nanostructures' band-gap, similar to their bulk counterpart. Several applications, including light-emitting diodes, lasers, and detectors, demonstrate the latent potential of perovskite nanostructures.

Recent developments in the evolving research field of nanomaterial-based perovskite are reviewed. Both hybrid organic-inorganic and all-inorganic perovskite nanostructures are discussed, as well as approaches to tune the optical properties by controlling the size and the shape of the perovskite nanostructures. Several applications, including light-emitting diodes, lasers, and detectors, demonstrate the latent potential of perovskite nanostructures.

Rapidly evolving fields of biomedical, energy, and (opto)electronic devices bring forward the need for deformable conductors with constantly rising benchmarks for mechanical properties and electronic conductivity. The search for conductors with improved strength and strain have inspired the multiple studies of nanocomposites and amorphous metals. However, finding conductors that defy the boundaries of classical materials and exhibit simultaneously high strength, toughness, and fast charge transport while enabling their scalable production, remains a difficult materials engineering challenge. Here, composites made from aramid nanofibers (ANFs) and gold nanoparticles (Au NPs) that offer a new toolset for engineering high strength flexible conductors are described. ANFs are derived from Kevlar macrofibers and retain their strong mechanical properties and temperature resilience. Au NPs are infiltrated into a porous, free-standing aramid matrix, becoming aligned on ANFs, which reduces the charge percolation threshold and facilitates charge transport. Further thermal annealing at 300 °C results in the Au-ANF composites with an electrical conductivity of 1.25 × 10⁴ S cm⁻¹ combined with a tensile strength of 96 MPa, a Young's modulus of 5.29 GPa, and a toughness of 1.3 MJ m⁻³. These parameters exceed those of most of the composite materials, and are comparable to those of amorphous metals but have no volume limitations. The plasmonic optical frequencies characteristic for constituent NPs are present in the composites with ANFs enabling plasmon-based optoelectronic applications.

A composite based on aramid nanofibers and gold nanoparticles reveals high mechanical properties and conductivity, being competitive with the best nanocomposites and amorphous metals. Gold nanoparticles are self-assembled in chains on aramid nanofibers, which reduces the percolation threshold. Thermal annealing further facilitates charge transport. The scalable fabrication of the free-standing composites sheets leads to ground-breaking materials for wearable electronics and plasmonics.

The charge-carrier balance strategy by interface engineering is employed to optimize the charge-carrier transport in inverted planar heterojunction perovskite solar cells. N,N-Dimethylformamide-treated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and poly(methyl methacrylate)-modified PCBM are utilized as the hole and electron selective contacts, respectively, leading to a high power conversion efficiency of 18.72%.

The extent to which the soft structural properties of metal halide perovskites affect their optoelectronic properties is unclear. X-ray diffraction and micro-photoluminescence measurements are used to show that there is a coexistence of both tetragonal and orthorhombic phases through the low-temperature phase transition, and that cycling through this transition can lead to structural changes and enhanced optoelectronic properties.