wangzhaowei

A low-cost carbon cloth is applied in perovskite solar cells (PSC) as a collector composite and degradation inhibitor. This study incorporates carbon fibers as a back contact in perovskite solar cells, which results in enhancement in all photovoltaic parameters. This material is suitable for large-scale fabrication of PSCs as it has shown an improved long-term stability when compared to the gold counterpart under elevated temperatures.

A family of porphyrins and benzoporphyrins bearing phenyl, thiophenyl, or bithiophenyl groups at their meso-positions are synthesized and systematically investigated for their potential use in bulk heterojunction solar cells (BHJ-SCs). Comparative studies of these compounds show that the introduction of the thiophenyl and bithiophenyl groups, and the extension of the porphyrin π-conjugated system significantly affect both photophysical and electrochemical properties. Binary conventional and ternary converted BHJ-SCs based on these compounds are fabricated and studied. Results show that remarkable enhancement of the device efficiency is achieved by using the thiophene-containing benzoporphyrin derivatives as additives for a poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester blend in the inverted BHJ-SCs. The optimum BHJ-SC exhibits a maximum energy conversion efficiency of 4.3%, corresponding to 19% enhancement of the conversion efficiency as compared with the benchmark BHJ-SCs.

Systematic structural modification of a series of porphyins and benzoporphyrins bearing phenyl, thiophenyl, or bithiophenyl meso-substituents enables understanding of structure–property relationship and fine-tuning of photophysical and electrochemical properties of the compounds. Device conversion efficiency can be improved by 19% when thiophene-substituted benzoporphyrin is used as an additive for ternary converted bulk heterojunction solar cells.

Portable electronic devices have become increasingly widespread. Because these devices cannot always be tethered to a central grid, powering them will require low-cost energy harvesting technologies. As a response to this anticipated demand, this study demonstrates transparent organic solar cells fabricated on flexible substrates, including plastic and paper, using graphene as both the anode and cathode. Optical transmittance of up to 69% at 550 nm is achieved by combining the highly transparent graphene electrodes with organic polymers that primarily absorb in the near-IR and near-UV regimes. To address the challenge of transferring graphene onto organic layers as the top electrode, this study develops a room temperature dry-transfer technique using ethylene-vinyl-acetate as an adhesion-promoting interlayer. The power conversion efficiency achieved for flexible devices with graphene anode and cathode devices is 2.8%–3.8% at for optical transmittance of 54%–61% across the visible regime. These results demonstrate the versatility of graphene in optoelectronic applications and it is important step toward developing a practical power source for distributed wireless electrical systems.

A visibly transparent, flexible solar cell with all-graphene electrodes is fabricated by combining the high optical transmittance of graphene with organic polymers that absorb primarily in the near-IR and near-IV regimes. The fabrication process is enabled by developing a universal room temperature dry graphene transfer method. The devices exhibit exceptional optical transmittance and mechanical flexibility.

Poly(Phenylene vinylene) anionic polyelectrolyte (PVBT-SO₃) was found to be an efficient hole extraction layer for inverted perovskite solar cells. It can be cast from an aqueous solution and does not require thermal annealing for improved device performance. The devices show maximum solar cell efficiency of 15.9% and exhibit improved stability under ambient conditions and enhanced charge extraction.

The typical broad absorption features have enabled halide perovskite to be a promising candidate of the next generational solar cell materials. However, the fundamental properties, upon which the photoelectric performance of perovskite device is based, are currently still not clear. Herein, the photovoltaic efficiencies in perovskite films with various thicknesses have been investigated to reveal a direct correlation between internal structure factors, such as crystal orientation, grain size, and photoelectric performance of perovskite films. It is found that the photovoltaic efficiency of perovskite films, especially with the optimal thickness around 300 nm, is significantly increased, which can be ascribed to the improved carrier transport properties resulting from the preferred crystal structure. When the film thickness diverges from 300 nm, the extra charge recombination with decreasing mobility leads to the reduction of photovoltaic efficiency again in perovskite solar cells. These results demonstrate crystal structure as one of the decisive roles in device properties, which are helpful to improve photovoltaic performance of perovskite solar cells.

The photovoltaic efficiency in perovskite films with various thicknesses has been investigated. It is shown that the photovoltaic efficiency of perovskite films can be significantly changed by the absorber layer thickness. By the analysis of the electron transfer mechanisms, a strong correlation between the internal structure factors of the perovskite layer and the photoelectric performance is revealed.

Organometal halide perovskite solar cells (PSCs) have shown much promise to be made semitransparent (ST) for a variety of applications. However, charge separation and collection are still inefficient from the ultrathin absorber layer and thus limit the ST-PSCs performance. Herein a type of hierarchical dual scaffolds is first reported to tackle this problem consisting of a quasi-mesoscopic inorganic (TiO₂) layer and a percolating organic (phenyl-C61-butyric acid methyl ester) manifold throughout the capped or filled perovskite bulk. It is demonstrated that the soft PCBM scaffold affords efficient charge separation due to the formation of a penetrating network intimately interfaced with perovskite crystals, meanwhile the quasi-mesoporous hard TiO₂ scaffold strongly based on the substrate further offers a continuous electron transport. As a result, the ST-PSCs based on the ultrathin perovskite layer (≈100 nm) with the dual-scaffolds have achieved an internal quantum efficiency of ≈100%, boosting the device efficiency to 12.32%. Furthermore, the real ST-PSCs fabricated by replacing the Ag electrode with a PEDOT:PSS transparent electrode have reached an efficiency of 8.21% with an average visible transmittance of 23%, placing among the highest performing devices of the kind reported to date.

Hierarchical organic phenyl-C61-butyric acid methyl ester–inorganic (TiO₂) dual scaffolds are constructed inside semitransparent perovskite solar cells with an ultrathin absorber layer (≈100 nm). The advanced strategy can improve the charge separation and collection of in perovskite solar cells and reach the efficiency of 12.32% with a 4.4% absolute increase.

It is shown that in the formamidinium (FA) lead iodide/titania heterostructure α-HC(NH₂)₂PbI₃/TiO₂ the organic layer-mediated interface, i.e., FAI/TiO₂, can induce photovoltaic diode effect via positive bias poling. The band gap of the heterostructure is reduced to zero upon the positive poling due to combined effects of ion diffusion, rotation of organic moieties, and ferroelectric redistribution. The perovskite part in the organic layer-mediated interface FAI/TiO₂ gives rise to a strong polarization of 18.69 μC cm⁻², compared to that (0.89 μC cm⁻²) in the inorganic layer-mediated interface PbI₂/TiO₂. The strong polarization of the organic layer-mediated interface is closely related to the diode effect associated with the reordering of the ferroelectric polarization and charge distribution, as a consequence of the mobility and rotation of organic moieties in FAI/TiO₂ upon the positive bias poling. The latter effect also provides an explanation on why the FAPbI₃-based devices can largely reduce the scanning hysteresis in the J–V curves (Yang et al., Science 2015, 348, 1234) and why the organic layer-mediated halide perovskite heterostructure is one of the most promising candidates for the fabrication of highly efficient solar cells or optoelectronic devices.

In the formamidinium (FA) lead iodide/titania heterostructure the organic layer-mediated interface, i.e., FAI/titania interface, can induce photovoltaic diode effect via positive bias poling due to combined effects of ion diffusion, rotation of organic moieties, and ferroelectric redistribution.

As demonstrated by Yabing Qi and co-workers in Okinawa Institute of Science and Technology Graduate University in article 1600117, mercury drop electrode current-voltage measurements reveal that moisture in ambient air causes Li-bis(trifluoromethanesulfonyl)-imide dopants to re-distribute across spiro-MeOTAD hole transport layer in perovskite solar cells, thereby significantly improving hole transport properties. These findings suggest that moisture-induced dopant redistribution is most likely the major cause responsible for the efficiency enhancement in perovskite solar cells when exposed to ambient air for several hours after fabrication, a common practice in the field.

Molecular hydrogen can be generated renewably by water splitting with an “artificial-leaf device”, which essentially comprises two electrocatalyst electrodes immersed in water and powered by photovoltaics. Ideally, this device should operate efficiently and be fabricated with cost-efficient means using earth-abundant materials. Here, a lightweight electrocatalyst electrode, comprising large surface-area NiCo₂O₄ nanorods that are firmly anchored onto a carbon–paper current collector via a dense network of nitrogen-doped carbon nanotubes is presented. This electrocatalyst electrode is bifunctional in that it can efficiently operate as both anode and cathode in the same alkaline solution, as quantified by a delivered current density of 10 mA cm⁻² at an overpotential of 400 mV for each of the oxygen and hydrogen evolution reactions. By driving two such identical electrodes with a solution-processed thin-film perovskite photovoltaic assembly, a wired artificial-leaf device is obtained that features a Faradaic H₂ evolution efficiency of 100%, and a solar-to-hydrogen conversion efficiency of 6.2%. A detailed cost analysis is presented, which implies that the material-payback time of this device is of the order of 100 days.

An artificial-leaf device is constructed by driving two carbon-based, bifunctional, and lightweight catalyst electrodes immersed in water with an assembly of solution-processed perovskite photovoltaics. The device delivers hydrogen gas at 100% Faradaic efficiency and with a solar-to-hydrogen efficiency of 6.2%, and a cost analysis suggests that the material-payback time can be of the order of 100 days.

Semitransparent perovskite solar cells based on smooth perovskite films and ultrathin Cu (1 nm)/Au (7 nm) metal electrode demonstrate an efficiency of 16.5%. When illuminated through the semitransparent perovskite cell, a near-infrared-enhanced silicon heterojunction solar cell operates with 6.5% efficiency, leading to a total perovskite/silicon four-terminal tandem efficiency of 23.0%.

Organic-inorganic metal halide perovskite solar cells show hysteresis in their current–voltage curve measured at a certain voltage sweep rate. Coinciding with a slow transient current response, the hysteresis is attributed to a slow voltage-driven (ionic) charge redistribution in the perovskite solar cell. Thus, the electric field profile and in turn the electron/hole collection efficiency become dependent on the biasing history. Commonly, a positive prebias is beneficial for a high power-conversion efficiency. Fill factor and open-circuit voltage increase because the prebias removes the driving force for charge to pile-up at the electrodes, which screen the electric field. Here, it is shown that the piled-up charge can also be beneficial. It increases the probability for electron extraction in case of extraction barriers due to an enhanced electric field allowing for tunneling or dipole formation at the perovskite/electrode interface. In that case, an inverted hysteresis is observed, resulting in higher performance metrics for a voltage sweep starting at low prebias. This inverted hysteresis is particularly pronounced in mixed-cation mixed-halide systems which comprise a new generation of perovskite solar cells that makes it possible to reach power-conversion efficiencies beyond 20%.

Inverted hysteresis is observed in mixed cation mixed halide perovskite solar cells, which show a power-conversion efficiency of 20%. It is attributed to charge accumulation and dipole formation at the perovskite/TiO₂ interface changing extraction barrier and recombination lifetimes in and close to the mesoporous scaffold.

Solution-processed few-layer MoS₂ flakes are exploited as an active buffer layer in hybrid lead–halide perovskite solar cells (PSCs). Glass/FTO/compact-TiO₂/mesoporous-TiO₂/CH₃NH₃PbI₃/MoS₂/Spiro-OMeTAD/Au solar cells are realized with the MoS₂ flakes having a twofold function, acting both as a protective layer, by preventing the formation of shunt contacts between the perovskite and the Au electrode, and as a hole transport layer from the perovskite to the Spiro-OMeTAD. As prepared PSC demonstrates a power conversion efficiency (η) of 13.3%, along with a higher lifetime stability over 550 h with respect to reference PSC without MoS₂ (Δη/η = −7% vs. Δη/η = −34%). Large-area PSCs (1.05 cm² active area) are also fabricated to demonstrate the scalability of this approach, achieving η of 11.5%. Our results pave the way toward the implementation of MoS₂ as a material able to boost the shelf life of large-area perovskite solar cells in view of their commercialization.

MoS₂ flakes are proposed as an active buffer layer in hybrid lead halide perovskite solar cells. By preventing the formation of shunt contacts between the perovskite and the metal electrode, MoS₂ flakes act as a protective layer to increase the cell stability, while also easing the hole collection at the anode. Such approach leads to efficient and stable perovskite solar cells.