Yurong Jiang

Passivated perovskite crystallization and stability in organic–inorganic halide solar cells by doping a donor polymer

Photovoltaic performance of planar perovskite hybrid solar cells (pero-HSCs) has been improved by mixing CH3NH3PbIxCl3−x and an electron donor polymer [N-9′′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiaz-ole)] (PCDTBT). PCDTBT contains lone pairs of electrons due to the presence of S and N atoms, which could passivate the trap states of the perovskite layer and thus reduce the number of film defects. A Stonehenge-like structure could be formed by the interaction of CH3NH3PbIxCl3−x and PCDTBT, developing more ordered orientation crystallization and a high quality film morphology. The doped solar cells are characterized by their excellent photovoltaic properties and enhanced stability. When the doping concentration is 0.3 mg mL−1, the fabricated solar cell device exhibits an outstanding power conversion efficiency (PCE) of 15.76%, which represents a significant improvement with respect to the magnitude of 16% obtained for the reference device.

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)–molybdenum oxide composite films as hole conductors for efficient planar perovskite solar cells

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)–molybdenum oxide (MoOx) composite films are used as hole transport layers in planar perovskite solar cells (PSCs) by simply incorporating solution-processed MoOx powders into a PEDOT:PSS solution. Compared to PEDOT:PSS based PSCs, the PEDOT:PSS–MoOx based PSC exhibits an obvious improvement in conversion efficiency, open circuit voltage, and fill factor. The morphology of perovskite films indicates that the film coverage has been improved due to the introduction of MoOx nanospots into the underlayer, which are regarded as the growing sites of the crystal nucleus of the perovskites during annealing. A PEDOT:PSS–MoOx based device with a power conversion efficiency of over 15% has been achieved, suggesting that the PEDOT:PSS–MoOx film is efficient as a hole transport layer in obtaining highly efficient planar perovskite solar cells.

Fine-tuning of polymer photovoltaic properties by the length of alkyl side chains

This paper reports the synthesis and characteristics of a series of alkyl-substituted planar polymers. The physical properties are carefully tuned to optimize their photovoltaic performance. Depending on the length of soluble alkyl side chains which modify the structural order and orientation substantially in polymer backbones, the device performance can be improved significantly. The tuning of HOMO energy levels optimized polymers’ spectral coverage of absorption and their hole mobility, as well as miscibility with fullerene; all these efforts enhanced polymer solar cell performances. The short-circuit current, Jsc for polymer solar cells was increased by adjusting polymer chain packing ability. It was found that films with well distributed polymer/fullerene interpenetrating network exhibit improved solar cell conversion efficiency. Enhanced efficiency up to 5.8% has been demonstrated. The results provide important insights about the roles of flexile chains in structure-property relationship for the design of new polymers to be used in high efficient solar cells.

Hybrid tapered silicon nanowire/PEDOT:PSS solar cells

A tapered silicon nanowire array (TSiNWs)/poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) hybrid solar cell was obtained based on alkali treatment processing. TSiNWs are engineered by combining electroless etching and an alkali solution in which the morphology of the tapered nanowire can be controlled by changing the immersing time. The results show that the alkali treatment could taper the silicon nanowires so that the polymer could conformally infiltrate into SiNWs via spin-coating. The experimental results demonstrate that the length and morphology of the SiNWs are key factors for improving the cell performance. Compared to the SiNWs/polymer hybird device, the TSiNWs/polymer hybrid solar cell can achieve a high power conversion efficiency of 6.87% and short-circuit current density of 26.7 mA cm−2. Therefore, tapered silicon nanowires are promising structures for realizing economically viable hybrid solar cells based on a very simple, scalable, and low-cost solution route.

Ferroelectric field effect of the bulk heterojunction in polymer solar cells

A ferroelectric field effect in the bulk heterojunction was found when an external electric field (EEF) was applied on the active layer of polymer solar cells (PSCs) during the annealing process of the active layer spin-coated with poly (3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester (P3HT:PCBM). For one direction field, the short circuit current density of PSCs was improved from 7.2 to 8.0 mA/cm2, the power conversion efficiency increased from 2.4 to 2.8%, and the incident photon-to-current conversion efficiency increased from 42 to 49% corresponding to the different EEF magnitude. For an opposite direction field, the applied EEF brought a minus effect on the performance mentioned above. EEF treatment can orientate molecular ordering of the polymer, and change the morphology of the active layer. The authors suggest a explanation that the ferroelectric field has been built in the active layer, and therefore it plays a key role in PSCs system. A needle-like surface morphology of the active film was also discussed.

Efficient and stable perovskite solar cells based on high-quality CH3NH3PbI3−xClx films modified by V2Ox additives

The method of preparing perovskite films in ambient air is of great importance to commercializing high-performance planar perovskite solar cells (PSCs). Herein, an efficient and stable inverted planar PSC has been prepared via a simple solution method in ambient air. A suitable vanadium oxide (V2Ox) aqueous solution is mixed with a CH3NH3PbI3−xClx precursor solution, resulting in an improvement in the CH3NH3PbI3−xClx film. Perovskite films with large crystal sizes could be obtained using V2Ox additives. The improvement in the performance of perovskite films is conducive to the separation and transmission of charge carriers. For PSCs, the highest power conversion efficiency (PCE) of 16.14% was obtained by controlling the proportion of V2Ox additives in ambient air. It is via a physical mechanism that V2Ox particles are dispersed in the perovskite crystal boundary, and the heterogeneous structure between CH3NH3PbI3−xClx and V2Ox is formed. In addition, the slow migration of iodide ions and stability of the perovskite films are also achieved. What merits more attention is that the PSCs with CH3NH3PbIxCl3−x:V2Ox (2.5 wt%) still maintain a high PCE after being stored for 1000 h, more than 70% of the initial one.

Efficiency Enhancement Mechanism for Poly(3, 4-ethylenedioxythiophene):Poly(styrenesulfonate)/Silicon Nanowires Hybrid Solar Cells Using Alkali Treatment

The efficiency enhancement mechanism of the alkali-treated Si nanowire (SiNW) solar cells is discussed and analyzed in detail, which is important to control the useful photovoltaic process. All the results demonstrate that the photovoltaic performance enhancement of alkali-treated SiNW device steps from the formation of the good core-shell heterojunction, which consequently enhances the junction area, promotes fast separating and transporting of electron and hole pairs, and reduces the carrier surface combination. It also indicates that alkali treatment for SiNWs is a promising processing as an economical method for the formation of good core-shell SiNW/polymer heterojunction.

Visible-light self-driven photodetector with enhanced performance based on CdS /Si nanowire heterojunction

In this article, the appealing application of the CdS/Si nanowire heterostructure as the self-driven photodetector was presented based on a facile successive ionic layer absorption and reaction. Compared to CdS /Si planar based device, photocurrent illuminated with light (532 nm) to dark-current ratio was enhanced significantly for CdS/Si nanowire based detector. Measurements of time resolved responses at zero bias were conducted, and the result also demonstrated that CdS/Si nanowire heterostructure had a high photosensitivity and fast photo-response as the self-driven visible light photodetector. Additionally, the corresponding mechanism for the phenomenon was discussed, and it is believed that such a high photoresponse comes from the improved optical absorption as well as the good carrier transfer and collection capability. The present CdS/Si core-shell heterojunction architectures are envisaged as potentially valuable candidates for next-generation photodectors.

Laser-Induced Morphology Change Based on Small Molecular Model Compounds Photo-Detector

Three small molecules furnished with a planar core, (5,6-bis(octyloxy) benzo[c][1,2,5] thiadiazole-4,7-diyl)bis(thiophene-5,2-diyl), and two wings, thieno [3,2-b]indole or carbazoles, were synthesized and used as sensing layer to make photo-detectors. The devices can detect photons at a wavelength band of 300–700 nm and exhibit a sensitive photo-response under on/off modulation. Near UV (405 nm) and visible (532 nm) laser beam were the light source in this work. The corrected responsivity reached up to 498 mA W-1 at 532 nm and 411 mA W-1 at 405 nm. Laser induced photo-current escalation was observed and investigated. For longer molecules, the photo-current was easy to be constant than the shorter reference counterpart. This special photo response mechanism was studied by alternating current impedance spectroscopy (IS) measurements and X-ray diffraction (XRD) exprements. Possible relations between molecular weight and various figures of merit for photo detectors were discussed.

Direct Growth of Feather-Like ZnO Structures by a Facile Solution Technique for Photo-Detecting Application

The feather-like hierarchical zinc oxide (ZnO) was synthesized via successive ionic layer adsorption and reaction without any seed layer or metal catalyst. A possible growth mechanism is proposed to explain the forming process of ZnO feather-like structures. Meanwhile, the photo-electronic performances of the feather-like ZnO have been investigated with the UV-vis-NIR spectroscopy, I-V and I-tmeasurements. The results indicate that feather-like ZnO hierarchical structures have good anti-reflection and excellent photo-sensitivity. All results suggest that the direct growth processing of novel feather-like ZnO is envisaged to have promising application in the field of photo-detector devices.