In-Situ Cyclized Polyacrylonitrile as an Electron Selective Layer for n-i-p Perovskite Solar Cell with Enhanced Efficiency and Stability.

In situ cyclized polyacrylonitrile (CPAN) is developed to replace n-type metal oxide semiconductors (TiO2 or SnO2) as an electron selective layer (ESL) for highly efficient and stable n-i-p perovskite solar cells (PSCs). The CPAN layer is fabricated via facile in situ cyclization reaction of polyacrylonitrile (PAN) coated on a conducting glass substrate. The CPAN layer is robust and insoluble in common solvents, and possesses n-type semiconductor properties with a high electron mobility of 4.13×10-3 cm2 V-1 s-1. With the CPAN as an ESL, the PSC affords a power conversion efficiency (PCE) of 23.12 %, which is the highest for the n-i-p PSCs with organic ESLs. Moreover, the device with the CPAN layer holds superior operational stability, maintaining over 90 % of their initial efficiency after 500 h continuous light soaking. These results confirm that the CPAN layer would be a desirable low-cost and efficient ESL for n-i-p PSCs and other photoelectronic devices with high performance and stability.

Facile Dimension Transformation Strategy for Fabrication of Efficient and Stable CsPbI3 Perovskite Solar Cells.

All-inorganic cesium lead triiodide (CsPbI3) perovskite has received increasing attention due to its intrinsic thermal stability and suitable band gap for photovoltaic applications. However, it is difficult to deposit high-quality pure-phase CsPbI3 films using CsI and PbI2 as precursors due to the rapid nucleation and crystal growth by the solution coating method. Here, a simple cation-exchange approach is employed to fabricate all-inorganic 3D CsPbI3 perovskite, where 1D ethylammonium lead (EAPbI3) perovskite is first solution-deposited and then transformed to 3D CsPbI3 via ion exchange between EA+ and Cs+ during thermal annealing. The large space between the PbI3- skeletons in 1D EAPbI3 favors the cation interdiffusion and exchange for the formation of pure-phase 3D CsPbI3 with full compactness and high crystallinity and orientation. The resulting CsPbI3 film exhibits a low trap density of state and high charge mobility, and the perovskite solar cell shows a power-conversion efficiency of 18.2% with enhanced stability. This strategy provides an alternative and promising fabrication route for the fabrication of high-quality all-inorganic perovskite devices.

Vacuum-Assisted Thermal Annealing of CsPbI3 for Highly Stable and Efficient Inorganic Perovskite Solar Cells.

Inorganic cesium lead iodide perovskite CsPbI3 is attracting great attention as a light absorber for single or multi-junction photovoltaics due to its outstanding thermal stability and proper band gap. However, the device performance of CsPbI3 -based perovskite solar cells (PSCs) is limited by the unsatisfactory crystal quality and thus severe non-radiative recombination. Here, vacuum-assisted thermal annealing (VATA) is demonstrated as an effective approach for controlling the morphology and crystallinity of the CsPbI3 perovskite films formed from the precursors of PbI2 , CsI, and dimethylammonium iodide (DMAI). By this method, a large-area and high-quality CsPbI3 film is obtained, exhibiting a much reduced trap-state density with prolonged charge lifetime. Consequently, the solar cell efficiency is raised from 17.26 to 20.06 %, along with enhanced stability. The VATA would be an effective approach for fabricating high-performance thin-film CsPbI3 perovskite optoelectronics.

Organic-inorganic hybrid perovskite for low-cost and high-performance xerographic photoreceptors.

Solution-processable organic-inorganic hybrid perovskites are being widely investigated for many applications, including solar cells, light-emitting diodes, photodetectors, and lasers. Herein, we report, for the first time, successful fabrication of xerographic photoreceptors using methylammonium lead iodide (CH3NH3PbI3) perovskite as a light-absorbing material. With the incorporation of polyethylene glycol (PEG) into the perovskite film, the ion migration inherent to the perovskite material can be effectively suppressed, and the resulting photoreceptor exhibits a high and panchromatic photosensitivity, large surface potential, low dark decay, and high environmental resistance and electrical cycling stability. Specifically, the energies required to photodischarge one half of the initial surface potential (E 0.5) are 0.074 µJ cm-2 at 550 nm and 0.14 µJ cm-2 at 780 nm, respectively. The photosensitivites outmatch those of the conventionally used organic pigments having narrow spectral responses. Our findings inform a new generation of highly efficient and low-cost xerographic photoreceptors based on perovskite materials.

Methylamine-assisted growth of uniaxial-oriented perovskite thin films with millimeter-sized grains.

Defects from grain interiors and boundaries of perovskite films cause significant nonradiative recombination energy loss, and thus perovskite films with controlled crystallinity and large grains is critical for improvement of both photovoltaic performance and stability for perovskite-based solar cells. Here, a methylamine (MA0) gas-assisted crystallization method is developed for fabrication of methylammonium lead iodide (MAPbI3) perovskite films. In the process, the perovskite film is formed via controlled release of MA0 gas molecules from a liquid intermediate phase MAPbI3·xMA0. The resulting perovskite film comprises millimeter-sized grains with (110)-uniaxial crystallographic orientation, exhibiting much low trap density, long carrier lifetime, and excellent environmental stability. The corresponding perovskite solar cell exhibits a power conversion efficiency (PCE) of ~ 21.36%, which is among the highest reported for MAPbI3-based devices. This method provides important progress towards the fabrication of high-quality perovskite thin films for low-cost, highly efficient and stable perovskite solar cells.

In Situ Deposition of CuBiS2 on Mesoporous TiO2 Film for Light Absorber in Solar Cells.

In this report, emplectite (CuBiS2) semiconductor has been deposited on mesoporous TiO2 using gas-solid reaction method. For the first time, CuCl2 and BiCl3 are solution-coated on mesoporous TiO2 films, and thereafter reacted with H2S gas in an H2S atmosphere. The CuBiS2 film is further confirmed using X-ray diffraction; thus, demonstrating the pure phase of CuBiS2. CuBiS2 film shows high spectral absorption with an energy gap (Eg) of 2.18 eV. Furthermore, devices have a structure consisting of FTO/compact-TiO2/mesoporous-TiO2/CuBiS2/P3HT/Ag have been fabricated and hence exhibit high photoresponse performance.

Ion Exchange/Insertion Reactions for Fabrication of Efficient Methylammonium Tin Iodide Perovskite Solar Cells.

The low toxicity, narrow bandgaps, and high charge-carrier mobilities make tin perovskites the most promising light absorbers for low-cost perovskite solar cells (PSCs). However, the development of the Sn-based PSCs is seriously hampered by the critical issues of poor stability and low power conversion efficiency (PCE) due to the facile oxidation of Sn2+ to Sn4+ and poor film formability of the perovskite films. Herein, a synthetic strategy is developed for the fabrication of methylammonium tin iodide (MASnI3) film via ion exchange/insertion reactions between solid-state SnF2 and gaseous methylammonium iodide. In this way, the nucleation and crystallization of MASnI3 can be well controlled, and a highly uniform pinhole-free MASnI3 perovskite film is obtained. More importantly, the detrimental oxidation can be effectively suppressed in the resulting MASnI3 film due to the presence of a large amount of remaining SnF2. This high-quality perovskite film enables the realization of a PCE of 7.78%, which is among the highest values reported for the MASnI3-based solar cells. Moreover, the MASnI3 solar cells exhibit high reproducibility and good stability. This method provides new opportunities for the fabrication of low-cost and lead-free tin-based halide perovskite solar cells.

Slot-Waveguide Silicon Nitride Organic Hybrid Distributed Feedback Laser.

One of the major barriers for a widespread commercial uptake of silicon nitride photonic integrated circuits for cost-sensitive applications is the lack of low-cost monolithically integrated laser light sources directly emitting into single-mode waveguides. In this work, we demonstrate an optically pumped organic solid-state slot-waveguide distributed feedback laser designed for a silicon nitride organic hybrid photonic platform. Pulsed optical excitation of the gain medium is achieved by a 450 nm laser diode. The optical feedback for lasing is based on a second-order laterally coupled Bragg grating with a slot-waveguide core. Optimized material gain properties of the organic dye together with the increased modal gain of the laser mode arising from the improved overlap of the slot-waveguide geometry with the gain material enable single-mode lasing at a wavelength of 600 nm. The straightforward integration and operation with a blue laser diode leads to a cost-effective coherent light source for photonic integrated devices.

Integrated silicon nitride organic hybrid DFB laser with inkjet printed gain medium.

The provision of a coherent light source is a prerequisite for a variety of photonic integrated circuits. The integration of semiconductor laser diodes in disposable photonic devices in fields such as biosensing is, however, impeded by the competitive pricing in this application area. In this work, we demonstrate lasing of an alternative laser light source, namely an integrated hybrid organic solid-state distributed feedback laser for a silicon nitride photonic platform. The laser is optically pumped with a high power 450 nm laser diode and emits in the visible at 630 nm into a waveguide taper to reduce the cross-section to a single mode geometry. Inkjet printing of the organic gain medium enables a local, cost-effective, and flexible processing technology. The fabrication of the presented coherent light source is CMOS compatible and therefore highly interesting for co-integrated sensing platforms.

A Cation-Exchange Approach for the Fabrication of Efficient Methylammonium Tin Iodide Perovskite Solar Cells.

Tin-based halide perovskite materials have been successfully employed in lead-free perovskite solar cells, but the overall power conversion efficiencies (PCEs) have been limited by the high carrier concentration from the facile oxidation of Sn2+ to Sn4+ . Now a chemical route is developed for fabrication of high-quality methylammonium tin iodide perovskite (MASnI3 ) films: hydrazinium tin iodide (HASnI3 ) perovskite film is first solution-deposited using presursors hydrazinium iodide (HAI) and tin iodide (SnI2 ), and then transformed into MASnI3 via a cation displacement approach. With the two-step process, a dense and uniform MASnI3 film is obtained with large grain sizes and high crystallization. Detrimental oxidation is suppressed by the hydrazine released from the film during the transformation. With the MASnI3 as light harvester, mesoporous perovskite solar cells were prepared, and a maximum power conversion efficiency (PCE) of 7.13 % is delivered with good reproducibility.

A Novel Strategy for Scalable High-Efficiency Planar Perovskite Solar Cells with New Precursors and Cation Displacement Approach.

Methylammonium iodide (MAI) and lead iodide (PbI2 ) have been extensively employed as precursors for solution-processed MAPbI3 perovskite solar cells (PSCs). However, the MAPbI3 perovskite films directly deposited from the precursor solutions, usually suffer from poor surface coverage due to uncontrolled nucleation and crystal growth of the perovskite during the film formation, resulting in low photovoltaic conversion efficiency and poor reproducibility. Herein, propylammonium iodide and PbI2 are employed as precursors for solution deposition of propylammonium lead iodide (PAPbI3 ) perovskite film. It is found that the precursors have good film formability, enabling the deposition of a large-area and homogeneous PAPbI3 perovskite film by a scalable dip-coating technique. The dip-coated PAPbI3 film is then subjected to an organic-cation displacement reaction, resulting in MAPbI3 film with high surface coverage and crystallinity. With the MAPbI3 film as the light absorber, planar PSCs are fabricated, and stabilized power conversion efficiencies of 19.27% and 15.68% can be achieved for the devices with active areas of 0.09 and 5.02 cm2 , respectively. The technology reported here provides a robust and efficient approach to fabricate large-area and high-efficiency perovskite cells for practical application.

Direct Conversion of CH3NH3PbI3 from Electrodeposited PbO for Highly Efficient Planar Perovskite Solar Cells.

Organic-inorganic hybrid perovskite materials have recently been identified as a promising light absorber for solar cells. In the efficient solar cells, the perovskite active layer has generally been fabricated by either vapor deposition or two-step sequential deposition process. Herein, electrochemically deposited PbO film is in situ converted into CH3NH3PbI3 through solid-state reaction with adjacent CH3NH3I layer, exhibiting a large-scale flat and uniform thin film with fully substrate coverage. The resultant planar heterojunction photovoltaic device yields a best power conversion efficiency of 14.59% and an average power conversion efficiency of 13.12 ± 1.08% under standard AM 1.5 conditions. This technique affords a facile and environment-friendly method for the fabrication of the perovskite based solar cells with high reproducibility, paving the way for the practical application.

Electrodeposition of PbO and its in situ conversion to CH3NH3PbI3 for mesoscopic perovskite solar cells.

The perovskite CH3NH3PbI3 was prepared on a mesoscopic TiO2 film, starting from electrodepositing PbO, to iodination to PbI2, and then interdiffusion reaction with CH3NH3I. The as-prepared film was used as a light absorber for the perovskite solar cells, exhibiting a high PCE of 12.5% under standard AM 1.5 conditions.

Molecular engineering of panchromatic isoindigo sensitizers for dye-sensitized solar cell applications.

A panchromatic dye was synthesized with an isoindigo core as a linker to bridge with a bis(4-tert-butylphenyl)phenylamine donor and a cyanoacetic acid acceptor for dye-sensitized solar cells, showing a broad spectral response and a high conversion efficiency of 7.55% under AM 1.5 conditions.

P3HT as hole transport material and assistant light absorber in CdS quantum dots-sensitized solid-state solar cells.

Regioregular poly(3-hexylthiophene) (P3HT) was employed as a hole transport material and assistant light absorber for the fabrication of a CdS quantum dot-sensitized solid-state solar cell, by which a power-conversion efficiency of 1.42% was achieved under an AM1.5 G (100 mW cm(-2)) condition.

Solid-state dye-sensitized solar cells fabricated by coupling photoelectrochemically deposited poly(3,4-ethylenedioxythiophene) (PEDOT) with silver-paint on cathode.

A PEDOT-based dye-sensitized solar cell (DSC) is successfully improved by coupling photoelectrochemically deposited PEDOT layer with an Ag paste-paint on the cathode. With a 9.3 µm thick mesoscopic nanocrystalline TiO(2) film, a maximum cell performance of 3.2% with relatively high V(oc) of around 780 mV is achieved.

Benzothiadiazole containing D-pi-A conjugated compounds for dye-sensitized solar cells: synthesis, properties, and photovoltaic performances.

Two D-pi-A conjugated molecules, BzTCA and BzTMCA, were developed through facile synthetic approaches for dye-sensitized solar cells. The investigation of the photophysical properties of BzTCA and BzTMCA both in dilute solutions and in thin films indicates that their absorption exhibits a wide coverage of the solar spectrum. The absorption features for BzTCA and BzTMCA commence at about 710 nm in solution, and at about 800 nm in the solid state. The absorption maxima (lambda(max)) for both BzTCA and BzTMCA on TiO(2) film are almost the same as those in dilute solution. Their HOMOs and LUMOs were found to partly overlap at the center of these dyes, which guarantees appreciable interactions between the donors and acceptors. The investigation of the performance of dye-sensitized solar cells fabricated from BzTCA and BzTMCA indicated that the power-conversion efficiencies are 6.04 % and 4.68 %, respectively, which could be comparable with the normal sensitizer N3. BzTMCA showed lower incident photon-to-electron conversion efficiency (IPCE) and J(sc) values relative to BzTCA, which is probably because of the weaker driving force of dye regeneration and electron injection process of BzTMCA. The IPCE responsive area reached nearly 800 nm, which provides great potential for further improvement of the photocurrent density and power-conversion efficiency. Our investigations demonstrate that both dyes BzTCA and BzTMCA could be promising candidates for dye-sensitized solar cells.

Novel TPD-based organic D-pi-A dyes for dye-sensitized solar cells.

A novel class of organic D-pi-A dyes employing a N,N,N',N'-tetraphenylbenzidine (TPD) unit as donor was designed and synthesized for dye-sensitized solar cells, which achieved a solar-to-electricity conversion efficiency (eta) of 5.63% in preliminary tests as compared to 6.42% for N3 dye under the same experimental conditions.

Novel organic dyes for efficient dye-sensitized solar cells.

Two novel metal-free organic dyes containing thienothiophene and thiophene segments have been synthesized. Nano-crystalline TiO2 dye-sensitized solar cells were fabricated using these dyes as light-harvesting sensitizers, and a high solar energy-to-electricity conversion efficiency of 6.23% was achieved.