Hybrid organic–inorganic halide perovskite crystals exhibit potential applications in amplified spontaneous emission (ASE) devices. The enhancement of the photoluminescence (PL) and full width at half maximum (FWHM) with the temperature dependent phase transition are beneficial to investigate the low threshold of ASE devices. However, the ASE performance and temperature dependent transition characteristics of perovskite films critically depend on morphology and crystallinity. In this paper, we propose vacuum-assisted thermal treatment to effectively prepare smooth, condense and well-crystalline MAPbI3 perovskite films. An obvious temperature dependent phase transition occurs in the vacuum annealed MAPbI3 perovskite films, leading to an increase in PL intensity, which could non-monotonically lower the threshold for ASE. Investigating the transient performance at the temperature dependent phase transition underlines an important step in optimizing these novel materials.

We demonstrate the use of TiO2 nanorods with well-controlled lengths as excellent electron extraction materials for significantly improving the performance of inverted polymer solar cells. The cells containing long nanorods outperform the devices using amorphous TiO2 particles as the electron extraction layer, mainly by a 2-fold increase in short-circuit current and fill factor. The enhanced charge extraction is attributed to the high electron mobility in crystalline nanorods and their preferential alignment during film formation. Furthermore, transient photocurrent studies suggest the presence of fewer interfacial and internal defects in the nanorod interlayers, which can effectively decrease carrier recombination and suppress electron trapping.

Organic–inorganic tri-halide perovskites (MAPbX3, where MA = CH3NH3, and X = Cl, Br, I) have shown promise as laser gain media. The laser characteristics of perovskite films are susceptible to their crystallinity and morphology. Herein, we demonstrate the morphology and crystallinity of perovskite films could be well-controlled in a modified sequential deposition process by using binary solvent mixtures involving N,N-dimethylmethanamide (DMF) and dimethylsulfoxide (DMSO). The highly crystalline and notably smooth MAPbI3 films on glass substrates yield outstanding amplified spontaneous emission (ASE) performance. The binary solvent engineering approach opens up new opportunities for the development of low-cost and high-efficient ASE devices based on perovskite materials.

A photocatalytic strategy has been developed to synthesize colloidal Ag-TiO2 nanorod composites in which each TiO2 nanorod contains a single Ag nanoparticle on its surface. In this rational synthesis, photoexcitation of TiO2 nanorods under UV illumination produces electrons that reduce Ag(I) precursor and deposit multiple small Ag nanoparticles on the surface of TiO2 nanorods. Prolonged UV irradiation induces an interesting ripening process, which dissolves the smaller nanoparticles by photogenerated oxidative species and then redeposits Ag onto one larger and more stable particle attached to each TiO2 nanorod through the reduction of photoexcited electrons. The size of the Ag nanoparticles can be precisely controlled by varying the irradiation time and the amount of alcohol additive. The Ag-TiO2 nanorod composites were used as electron transport layers in the fabrication of organic solar cells and showed notable enhancement in power conversion efficiency (6.92%) than pure TiO2 nanorods (5.81%), as well as higher external quantum efficiency due to improved charge separation and transfer by the presence of Ag nanoparticles.

This study reported a novel fluorinated copolymer (FTQ) and shown it to exhibit a significantly higher open circuit voltage (VOC) in bulk heterojunction solar cells with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) compared to the low band-gap polymer Thiophene–Quinoxaline (TQ). Fluorination lowers the polymer HOMO level effectively which pushes down the highest occupied molecular orbital (HOMO) level of the TQ from −5.36 eV to −5.51 eV and increases the relative dielectric constant from 4.2 to 5.5, resulting in a high VOC. The highest VOC of 950 mV was achieved in the FTQ/PCBM solar cell device. For these optimized blends, the device made of FTQ:PC71BM with a 1:1 weight ratio yielded a high power conversion efficiency of 5.3% after a very short time thermal annealing process. These findings will be of importance for achieving high-performance of polymer solar cells by functional group substitution in low band gap polymers.

Porous Y2O3:Er plates with enhanced upconversion luminescence properties have been synthesized through a hydrothermal method, followed by a post thermal treatment. The as-obtained products exhibit red (650–670 nm,4F9/2→4I15/2) and green emission bands (520–570 nm, 2H11/2, 4S3/2→4I15/2) under 980 nm pumping. The shape and size of the pores in the plates can be tuned by controlling the reaction time in the autoclave. Moreover, the porous structure induces surface defects, which greatly affect the upconversion luminescence intensity and decay time. The potential mechanism for the effects of surface defects on the upconversion intensity and decay time was investigated, which could be a new complement for upconversion luminescence.Highlights► The upconversion material with porous structure Y2O3:Er has been hydrothermally synthesized. ► The pore size and shape can be tuned by controlling the reaction time in the autoclave. ► The mechanism of surface defects effect the upconversion intensity and life time.was analyzed. ► They could be a new complement for UC luminescence.

•We report the alleviation of EL efficiency rolling off attributing to phosphorescent sensitization.•We show the principle for management of triplet and singlet excitons to produce a high efficient white light emission.•We show how the EL efficiency changed as NPB layer thickness increasing.•The triplet lifetime of Ir(ppy)3decreased as DCJTB dopant increasing.We report efficient and color-stable white organic light-emitting diodes (WOLEDs) by an approach combining the concepts of exciton management and phosphorescent sensitization to achieve 100% internal quantum efficiency and reduce efficiency roll-off. The approach employs a layer of 4-bis-(1-naphthyl-N-phenylamino)-biphenyl (NPB) as a fluorescent blue emitter to collect all singlet excitons for blue emission, and fac-tris(2-phenylpyridine) iridium(III) (Ir(ppy)3) as a phosphorescent emitter and sensitizer in other layer to harvest all triplet excitons for generating green light and sensitizing a fluorescent dye 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4Hpyran (DCJTB) for orange–red emission. By carefully adjusting the concentration of DCJTB and the thickness of the NPB layer, efficiency roll-off has been reduced and efficient balanced white light has been produced from the device ITO/PEDOT:PSS (30 nm)/poly(vinylcarbazole) (PVK):Ir(ppy)3:DCJTB (100:5:0.4 in wt.) (60 nm)/NPB (4 nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) (10 nm)/tris(8-hydroxyquinoline)aluminum (Alq3) (20 nm)/LiF (1 nm)/Al. The operating principles have been studied and the results show that the long diffusion length of triplet excitons and long-range nonradiative energy transfer between the triplets of the phosphorescent emitter and the singlets of the fluorescent dye are crucial to realize white light emission.

The surface plasmonic effect and scattering effect of gold nanorods (AuNRs) on the performance of bulk heterojunction photovoltaic devices based on the blend of polythiophene and fullerene are investigated. AuNRs enhance the excitation since the plasmonic effect increases the electric field, mainly in the area near the interface between the active layer and AuNRs. The results show that the incident photo-to-electron conversion efficiency (IPCE) obviously increases for the device with a layer of gold nanorods, resulting from the plasmonic effect of AuNRs in the range of 500–670 nm and the scattering effect in the range of 370–410 nm. The power conversion efficiency (PCE) is increased by 7.6% due to the near field effect of the localized surface plasmons (LSP) of AuNRs and the scattering effect. The short circuit current density is also increased by 9.1% owing to the introduction of AuNRs. However, AuNRs can cause a little deterioration in open circuit voltage.

In this paper, the morphology evolution of [6,6]-phenyl-C-61(or 71)-butyric acid methyl ester (PC61BM or PC71BM) in poly(3-hexylthiophene) (P3HT) annealed at different temperatures was investigated. One result which was observed is that PCBM clusters aggregate more readily at higher annealing temperatures. The aggregation of PCBM could be avoided after coating the Al layer on the active layer, which is due to the hindering effect of the Al layer for the formation of PCBM clusters. SEM images show that the active layer with Al coating is smoother than that without Al layer. The performance of so-fabricated devices was analyzed with different annealing temperatures. Open-circuit voltage, fill factor and power conversion efficiency (PCE) of the devices were improved subsequently with increased annealing temperatures, while the absorption intensity of the devices was also improved. The P3HT:PC61BM and P3HT:PC71BM blend devices had highest PCEs of 4.55% and 4.84%, respectively. Crystallinity of the active layer is raised with higher annealing temperatures, which may result in the increased performance of devices.Highlights► PCBM clusters aggregate more readily at higher annealing temperatures. ► The aggregation of PCBM could be avoided after coating the Al layer on the active layer. ► PCE of the devices were improved subsequently with increased annealing temperatures. ► The P3HT:PC61BM and P3HT:PC71BM blend devices had obtained the PCE of 4.55% and 4.84%, respectively.

Hybrid solar cells using monodisperse Cu2S nanodisks compositing with the mixture of poly (3-hexylthiophene):1-(3-methoxycarbonyl) propyl-1-pheny [6,6] C61 (P3HT:PC60BM) as the active layer have been fabricated and characterized. The hybrid solar cells exhibit the highest efficiency of 1.35% when the weight ratio of P3HT:PC60BM:Cu2S is 1:0.8:0.224. The power conversion efficiency (PCE) of nanocomposite device is increased 22.7% comparing with that of the device based on pure P3HT/PC60BM. It is due to that the effect of high-quality Cu2S nanodisks with good dispersity contributes the increased electronic transportation in the active layer and results in the enhancement in photovoltaic performance. We also investigated the morphology of photoactive layer by microscope; it is found that the dispersity of nanomaterial in active layer is very important for device performance and improvement of carrier mobility.

We report the electrical bistability of cadmium sulfide (CdS) nanoparticles (NPs) capped by dodecanethiol, which are sandwiched between aluminum tris (8-hydroxyquinoline) (Alq3) layers. The current density–voltage (J–V) characteristics of the device with Al/Alq3/CdS NPs/Alq3/Al structures show the high- and low-conducting state at the same voltage, and the two states are reproducible by applying different negative sweeping voltages. The Ohmic model and the space–charge limited model are proposed and supported by the current density–voltage results, which give a possible transport mechanism for the electrical bistability of our devices.

The photovoltaic properties of solar cell based on the blends of poly[2-methoxy-5-(2-ethylhexoxy-1,4-phenylenevinylene) (MEH-PPV), fullerene (C60), and ZnCdTe-alloyed nanocrystals were investigated. Comparing the spectral response of photocurrent of the MEH-PPV:C60(+ZnCdTe) nanocomposite device with that of the devices based on MEH-PPV:C60and pristine MEH-PPV, one can find that the nanocomposite device exhibits an enhanced photocurrent. In comparing the composite devices with different ZnCdTe:[MEH-PPV + C60] weight ratios of 10 wt% (D1–1), 20 wt% (D1–2), 40 wt% (D1–3), and 70 wt% (D1–4), it was found that the device D1–3exhibits the best performance. The power conversion efficiency (η) is improved doubly compared with that of the MEH-PPV:C60device.

Transport mechanism of photogenerated carriers in composite films based on Poly [2-methoxy,5-(2′-ethylhexyloxy)-1,4,-phenylene-vinylene] (MEH-PPV) doped with fullerene (C60) is investigated by double-light-pulse induced photocurrent responses. Charge accumulation is found in low concentration ranges of C60, while at high C60 concentration (50 wt%), the same feature is completely absent. Charge accumulation at the interface between MEH-PPV and C60 directly reduces the external quantum efficiency of composite devices.

In this paper, we synthesized a novel type II cuprous sulfide (Cu2S)–indium sulfide (In2S3) heterostructure nanocrystals with matchstick-like morphology in pure dodecanethiol. The photovoltaic properties of the heterostructure nanocrystals were investigated based on the blends of the nanocrystals and poly(2-methoxy-5-(2′-ethylhexoxy)-p-phenylenevinylene) (MEH-PPV). In comparison with the photovoltaic properties of the blends of Cu2S or In2S3nanocrystals alone and MEH-PPV, the power conversion efficiency of the hybrid device based on blend of Cu2S–In2S3and MEH-PPV is enhanced by ~3–5 times. This improvement is consistent with the improved exciton dissociation or separation and better charge transport abilities in type II heterostructure nanocrystals.

The photocurrent spectral responses of poly[2-methoxy-5-(2′-ethyl-hexoxy-p-phenylene vinylene]:fullerene (C60) composites are measured as a function of C60 concentration. At low concentration, the relationship between the external quantum efficiency (EQE) and absorption spectra is exhibited as the strengthened antibatic effect, and the EQE of the composite devices declines with increasing concentration of C60. At higher concentration, however, the maximum EQE gradually coincides with the absorption peak (symbatic response) and the EQE of composite devices begins to increase with increasing C60 concentration. It is proposed that at low concentration, dopant C60 increases the self-absorption rate of composite films, and charge trapping by C60 molecules causes the loss of efficiency. At high C60 concentration, the large-scale aggregations in composite films build pathways for charge carrier transport to respective electrodes, inhibiting the self-absorption effect and charge recombination on C60.

The insertion layer of cadmium sulfide (CdS) between polymer–fullerene blend and Al electrode is used to enhance the short-circuit current (Isc) and the power conversion efficiency (PCE). The solar cells based on the blend of poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and C60 with the function layer of CdS (∼10 nm) shows the open-circuit voltage (Voc) of ∼0.7 V, short-circuit current (Isc) of ∼4.6 mA/cm2, filling factor (FF) of ∼0.28, and the power conversion efficiency (PCE) of ∼5.3% under monochromatic light (532 nm) photoexcitation of about 16.7 mW/cm2. Compared to cells without the CdS layer, the power conversion efficiency increases about an order of magnitude. The thickness of CdS layer was varied from 10 to 40 nm using e-beam deposition, and we obtained optimum current density–voltage characteristics for 10 nm thick CdS layer.

This study reported a novel fluorinated copolymer (FTQ) and shown it to exhibit a significantly higher open circuit voltage (VOC) in bulk heterojunction solar cells with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) compared to the low band-gap polymer Thiophene–Quinoxaline (TQ). Fluorination lowers the polymer HOMO level effectively which pushes down the highest occupied molecular orbital (HOMO) level of the TQ from −5.36 eV to −5.51 eV and increases the relative dielectric constant from 4.2 to 5.5, resulting in a high VOC. The highest VOC of 950 mV was achieved in the FTQ/PCBM solar cell device. For these optimized blends, the device made of FTQ:PC71BM with a 1:1 weight ratio yielded a high power conversion efficiency of 5.3% after a very short time thermal annealing process. These findings will be of importance for achieving high-performance of polymer solar cells by functional group substitution in low band gap polymers.