Hybrid Organic-inorganic Solar Cells Research Articles

Electron-Selective Epitaxial/Amorphous Germanium Stack Contact for Organic-Crystalline Silicon Hybrid Solar Cells

ABSTRACT: Carrier transport properties can be improved through suppressing the charge carrier recombination and decreasing the contact resistance using the proper carrier-selective contact. In this work, an epitaxial/amorphous germanium (epi/a-Ge) stack thin film is introduced into the rear surface of organic-inorganic hybrid (OIH) solar cells as an efficient electron-selective contact. This novel electron-selective stack contact simultaneously contributes low recombinative and resistive losses through a three-material system composed of n-type silicon (n-Si), epitaxial silicon germanium (epi-SiGe), and amorphous germanium (a-Ge), which promotes the tailoring of band structures, the passivation of surface dangle bond defects and the formation of Ohmic contact. The results result in obvious improvement in the open-circuit voltage (Voc) (from 549.5 mV to 643.0 mV) and fill factor (FF) (from 70.5% to 75.4%), corresponding to the increase in the power conversion efficiency (PCE) of OIH solar cells (from 10.3%...

Doped silicon nanoparticles for enhanced charge transportation in organic-inorganic hybrid solar cells

In this work, we have added p-type and n-type Si nanoparticles (NPs) obtained from cryomilling, in poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) organic photovoltaic cell at different weight ratios and their effect on organic-inorganic hybrid solar cell device parameters has been evaluated. It is observed that the addition of p-type nanoparticles tailors the energy band alignment at the P3HT/NP interface which provides efficient charge carrier transport enhancing the photo-conversion efficiency by more than 21%. Enhancement is reflected by an improvement in short-circuit current by ∼35% with respect to reference P3HT:PC61BM device without Si NPs. However, for n-type NPs where the optimum cascading band alignment does not occur, only 10% improvement in photo-conversion efficiency is observed. This work provides insight into how the performance of organic solar cells can be tailored by size factor as well as byenergy level tuning of the added nanoparticles.

Effect of localized surface plasmon resonance from incorporated gold nanoparticles in PEDOT:PSS hole transport layer for hybrid solar cell applications

We report optical and structural properties of poly (3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) incorporated gold nanoparticles capped by citrates (Au-citrates) as hole transport layer for hybrid organic-inorganic solar cell applications. PEDOT:PSS and Au-citrates both are water solution and the mixed are done in 2.378 wt%, 2.978 wt% and 3.144 wt% of Au-citrates. Plasmonic peak in the wavelength area of ∼525 nm for Au-citrates is found quite stable after addition of iso-propanol for wettability purpose. In our result, enhanced absorbance spectra of PEDOT:PSS incorporated Au-citrates indicates the effect of localized surface plasmon resonance from Au-citrates and it is estimated to enhance performance of hybrid solar cell efficiency. Optical properties of the thin films in hybrid solar cell device are done in the structure of ITO/ZnO/P3HT:PCBM(active layer)/(PEDOT:PSS:Au-citrates). The complete layer structure shows the enhancement of optical property in all UV-vis region in comparison to that structure without Au-citrates.

Effective charge collection area during conductive and photoconductive atomic force microscopy

Conductive atomic force microscopy (C-AFM) has been widely used to map the nanoscale electrical properties of conducting polymers, nanomaterials, and organic electronic devices. While these measurements provide valuable insight into the spatial dependence of electrical performance, reported current densities and electrical conductivities measured by C-AFM are consistently much higher than those measured at the macroscopic scale. Here, we demonstrate that these anomalously high current densities and conductivities arise from ignoring current spreading and hence underestimating the current-carrying area. We present a simple experimental means of estimating the effective charge collection area during C-AFM measurements. Using semiconducting polymer poly(3-hexylthiophene) films as a test case, we find that the effective charge collection area can be as much as three orders of magnitude larger than the mechanical contact area between the probe and the film. Calibrated conductivity maps are obtained, with a quantitative correspondence with accepted values, and C-AFM photocurrent measurements of a nanostructured hybrid organic-inorganic solar cell active layer yield short-circuit current densities that match those reported for macroscopic devices. Finally, we address the observation that current spreading increases the effective charge collection area beyond the size of the probe-sample contact but does not preclude an imaging resolution below 10 nm.

(Invited) Improved Interfaces in Multilayered Organic-Inorganic Hybrid Solar Cells with π-Conjugated Polymers-Antimony Sulfide-Strontium Titanate-Titanium Oxide

Organic-inorganic hybrid solar cells composed of glass/F-doped SnO2/TiO2/ SrTiO3/Sb2S3/ poly[(3-hexylthiophene)-2,5-diyl]/poly[3-(3-carboxypropyl)thiophene-2,5-diyl]/Au have been prepared and evaluated their photovoltaic performance. Insertion of SrTiO3 layer between TiO2 and Sb2S3 interface resulted in the enhancement of the open circuit voltage (Voc ) from 0.61 V to 0.70 V. The thickness, surface roughness, and sea-island structures of the Sb2S3 layer were optimized in terms of transmittance, reflectivity, short circuit current density (Jsc ), fill factor (FF) and power conversion efficiency (PCE) by changing the precursor concentration and rotation speed for spin-coating of the Sb2S3 layer. Through the above optimization, enhancements of Jsc from 8.6 mA cm-2 to 13.6 mA cm-2 and FF from 0.56 to 0.61 in addition to the improvement of PCE from 3.0% to 6.1% as compared with the device without the SrTiO3 layer were achieved.

Surface plasmon resonance effect of silver nanoparticles on the enhanced efficiency of inverted hybrid organic–inorganic solar cell

We investigate the effects of silver nanoparticles capped by 1-octanethiol (AgSC8) incorporated into the active layer of regioregular poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) in the fabrication of an inverted hybrid solar cell. The localized surface plasmon resonance (LSPR) excited in AgSC8 is expected to enhance the photon absorption as well as improve the efficiency of exciton generation and dissociation in this type of solar cell. The measured UV–visible absorption spectra show that photoactive polymer (P3HT:PCBM) layers with 2.09[Formula: see text]wt.% and 3.34[Formula: see text]wt.% AgSC8 incorporations remain homogeneous, while it appears aggregated with 5.02[Formula: see text]wt.% AgSC8 incorporation. Under the illumination of 100[Formula: see text]mW/cm2 simulated solar irradiation, the fabricated device exhibits an increased open circuit voltage ([Formula: see text] from 0.327[Formula: see text]V to 0.665[Formula: see text]V for the case with 3.34[Formula: see text]wt.% AgSC8 incorporation and an improved device power conversion efficiency (PCE) from 1.01% to 1.92%. These results suggest the favorably role of AgSC8 in photo-generation of exciton and its dissociation at the LSPR frequency of AgSC8. The decrease of short circuit current density ([Formula: see text] from 10.316[Formula: see text]mA/cm2 to 8.668[Formula: see text]mA/cm2 nevertheless implies reduced conductivity due to AgSC8 incorporation.

Recent progress in synthetic methods and applications in solar cells of Ag2S quantum dots

Ag2S quantum dot is a semiconductor with narrow band-gap, high chemical stability, broad light absorption, photovoltaic effect and photoluminescence, which makes it a good photovoltaic material for fabricating solar cells. Many works have been conducted to demonstrate the synthesis of Ag2S nanostructure, as well as their applications in solar cells. In this article, the recent development of methods for synthesizing Ag2S quantum dots and Ag2S-based solar cells is reviewed. Especially metal oxide/Ag2S-based solar cells, Ag2S quantum dots, dye co-sensitized solar cells and inorganic-organic hybrid solar cells have been detailed. Ag2S quantum dots, with broad light absorption band and extensive absorption coefficient, have shown large potential in fabricating quantum dot-sensitized solar cells as well as polymer solar cells.

Enhanced photovoltaic performance of PEDOT:PSS/Si solar cells using hierarchical light trapping scheme

Organic-inorganic hybrid solar cells have attracted tremendous research attention in recent years owing to their low fabrication cost and potentially high performance. In the present study, hierarchical structures consisting of nanostructures made over micro-textured pyramidal (MPs) silicon surface are used in PEDOT:PSS/Si heterojunction solar cells to achieve a power conversion efficiency (PCE) up to 10.26%. The combined micro-nanostructuring concept provides a superior light trapping ability (compared to only micro-textured Si), mechanical stability (compared to only Si nanowire arrays concept), increased junction area and hence improved photovoltaic (PV) characteristics including short-circuit photocurrent and PCE. Silver assisted electroless wet chemical etching is used to produce nanostructures of different length over the micro-pyramidal Si. The hierarchically structured surfaces have one-fourth reflectance in broad spectral range (300–1100 nm) as compared to micro-pyramidal Si (∼13%) arising from the enhanced light trapping properties of nanostructures owing to multiple interaction of incident light and dimensions equivalent to sub-wavelength structures. Moreover, the hierarchical structures exhibit excellent omnidirectional light trapping ability at wide range of angle of incidence of light and spectral wavelength, which is essential for practical PV applications. This has been demonstrated using solar weighted reflectance corresponding to AM 1.5G solar flux and compared with that of MPs surface. Influence of nanostructuring time on reflectance and PV performance of the solar cell has been investigated. A significant enhancement in PCE up to 0.78% (absolute) and over 8.0% (relative) could be achieved as compared to MPs-Si based hybrid solar cell (control cell) for an optimized hierarchically structured Si surfaces. It is established that an optimal trade-off between reduced reflectance of such surfaces and solar cell performance parameters is essential. Longer nano-structuring despite exhibiting a better light trapping properties results in poor cell efficiency as the nano-structuring also leads to increased surface area and non-conformal coating of the polymer. Hence, increase in photocurrent is also accompanied by a simultaneous deterioration of other cell parameters such as open circuit voltage and fill factor of the device. Nevertheless, a properly designed hierarchical-structured device paves a promising way for developing low-cost and efficient PV applications in the future.

(Invited) Improved Interfaces in Multilayered Organic-Inorganic Hybrid Solar Cells with π-Conjugated Polymers-Antimony Sulfide-Strontium Titanate-Titanium Oxide

We have developed various organic-inorganic hybrid solar cells using Sb2S3-based composites with π-electronic molecules [1,2]. For examples, utilization of zinc phthalocyanine (ZnPC) for the hybrid solar cell composed of glass/indium-tin-oxide (ITO)/TiO2/Sb2S3/ZnPC/Au achieved long durability with keeping the relative power conversion efficiency (PCE) of 90% after the stability test under 1 sun at 63 °C at a relative humidity of 50% for 1,500 h [1]. Using La-decorated Sb2S3 for hybrid solar cell composed of glass/F-doped SnO2 (FTO)/TiO2/La-decorated Sb2S3/poly[(3-hexylthiophene)-2,5-diyl] (P3HT)/poly[3-(3-carboxypropyl)thiophene-2,5-diyl] (P3CT)/Au resulted in 33% improvement of PCE as compared to that of the non-decorated Sb2S3 because of lowering the resistance at the interface, which was confirmed by the impedance analyses [2]. While doping of Zn into Sb2S3 attained 57% enhancement of PCE. This result is ascribed to the effective lowering the bulk-resistance [2]. In this context, we newly inserted SrTiO3 layer between TiO2 and Sb2S3 interface and found the enhancement of the open circuit voltage (VOC ) from 0.61 V to 0.74 V. Temperature dependence of VOC for SrTiO3-inserted device indicated the maximum voltage was 1.7 V, which had been estimated by extrapolation of the line to 0 K. For further improvement of the photovoltaic performance, we modified the thin-film making process for Sb2S3 layer from the previously reported procedures [1,2]. After the spin-coating of the precursor solution of SbCl3-thiourea complex in DMF onto the SrTiO3 layer, heat treatment at 220 °C under vacuum was newly performed. The thickness, surface roughness, and sea-island structure were optimized by their uv-vis measurement, AFM, TEM observations, and current density-voltage (J-V) characteristics in terms of transmittance, reflectivity, and short circuit current density (JSC ) by changing the spin-coating speed, duration of heating, and so on. Through the optimization, remarkable enhancement of JSC from 10.7 mA cm-2 to 13.6 mA cm-2 and improvement of PCE from 4.7% to 6.1% were achieved. [1] A. Hayakawa, M. Yukawa, and T. Sagawa, ECS J. Solid-State Technology, 6(4), Q35-Q38 (2017). [2] M. Yukawa, A. Hayakawa, and T. Sagawa, ECS Trans., 77(11), 653-659 (2017).

Determination of Carrier Lifetimes in Organic-Inorganic Hybrid Solar Cells Based on Sb2S3 by Using the Time-Resolved Photocurrent

This paper presents organic-inorganic hybrid solar cells (SCs) based on ZnO/Sb2S3/P3HT heterojunctions. The ZnO and the Sb2S3 layers were grown using atomic layer deposition (ALD). Although four cells were fabricated on one substrate by using the same process, their open-circuit voltages (V OC ) and short-circuit current densities (J SC ) were different. The SC with a high V OC has a low J SC . The causes of the changes in the V OC and the JSC were investigated by using photoluminescence (PL) spectroscopy and optically-biased time-resolved photocurrent (TRPC) measurements. The PL results at 300 K showed that the emission positions of the Sb2S3 layers in all cells were similar at approximately 1.71 eV. The carrier lifetime of the SCs was calculated from the TRPC results. The lifetime of cell 4 with the highest J SC decreased drastically with increasing intensity of the continuous-wave optical bias beam. Therefore, the defect states in the ZnO layer contribute to the J SC , but degrade the V OC .

Comprehensive investigation of core-shell dimer nanoparticles size, distance and thicknesses on performance of a hybrid organic-inorganic halide perovskite solar cell

Significant performance enhancement in an ultrathin perovskite (CH3NH3PbI3) solar cell is done using plasmonic embedded core–shell dimer nanoparticles. Three-dimensional finite difference time-domain (FDTD) method is used. A perovskite absorber with a volume of 400 × 400 × 200 nm3 is considered. At first, a cell with one embedded nanoparticle is simulated. Absorptance of CH3NH3PbI3 absorber and gold nanoparticle are obtained. An optimization is done. Then a cell with embedded dimer nanoparticles is evaluated. The results show higher photocurrent enhancement for that in compared to a cell with one embedded nanoparticle. To further photocurrent enhancement, gold-SiO2 core–shell nanoparticles are used. Photocurrents of 23.37 mA cm−2, 23.3 mA cm−2, 22.5 mA cm−2 and 21.47 mA cm−2 are obtained for a cell with two embedded core–shell nanoparticles with core radius of 60 nm and shell thickness of 2 nm, 5 nm, 10 nm and 20 nm, respectively. It is important to mention that the photocurrent is 17.9 mA cm−2 for reference cell and 19.8 mA cm−2 for a cell with one embedded nanoparticle. Higher photocurrent is due to the near-field plasmonic effect.

Bulk-heterojunction hybrid solar cells with non-toxic, earth abundant stannite phase CuZn2AlS4 nanocrystals

Here we report the application of stable stannite phase CuZn2AlS4 (CZAS) nanocrystals (NCs), prepared by using a facile hydrothermal approach, as electron acceptor and photo-active material in organic-inorganic hybrid solar cells, for the first time. The photovoltaic (PV) performance of devices have been investigated in both inverted and classical device architectures with Poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and Poly(3-hexylthiophene-2,5-diyl) (P3HT) electron donor materials. First, PV devices of inverted architectures have been fabricated using MEH-PPV and CZAS NCs and their blending ratio has been optimized for optimum power conversion. Furthermore, devices of classical architecture have been also fabricated using optimized ratio of the CZAS NCs. A significant improvement in device efficiency has been observed on blending CZAS NCs in photoactive layer. Devices without CZAS NCs exhibited 1.72% whereas on incorporation of CZAS NCs 3.25% device efficiency has been observed.

A combined experimental and theoretical investigation of donor and acceptor interface in efficient aqueous-processed polymer/nanocrystal hybrid solar cells

As a route to improving the energy conversion of organic-inorganic hybrid-solar cells, we have tested the performance of poly (phenylene vinylene) (PPV), poly(2,5-thienylene vinylene) (PWTV) polymers and CdTe nanocrystal devices produced via aqueous-processing. It is found that small differences in the conformation of the sensitizer lead to dramatic effects on the solar cell efficiency. Using a combination of UV-Vis absorption spectroscopy and first-principles non-adiabatic molecular dynamics (NAMD) based on time-dependent density-functional theory (TDDFT), PPV is found to have a longer electron injection and recombination time despite seeming to have a better energy alignment with the substrate, which leads to a higher devices performance than PWTV. The present results shed new light on the understanding of organic-inorganic hybrid-solar cells and will trigger further experimental and theoretical investigations.

Possibility to Use Hydrothermally Synthesized CuFeS2 Nanocomposite as an Acceptor in Hybrid Solar Cell

Here we have approached the plausible use of CuFeS2 nanocomposite as an acceptor in organic–inorganic hybrid solar cell. To produce CuFeS2 nanocomposite, hydrothermal strategy was employed. The room-temperature XRD pattern approves the synthesized material as CuFeS2 with no phase impurity (JCPDS Card no: 37-0471). The elemental composition of the material was analyzed from the TEM-EDX data. The obtained selected area electron diffraction (SAED) planes harmonized with the XRD pattern of the synthesized product. Optical band gap (4.14 eV) of the composite from UV–Vis analysis depicts that the synthesized material is belonging to wide band gap semiconductor family. The HOMO (− 6.97 eV) and LUMO (− 2.93 eV) positions from electrochemical study reveal that there is a possibility of electron transfer from MEH-PPV to CuFeS2. The optical absorption and photoluminescence spectra of MEH-PPV:CuFeS2 (donor:acceptor) composite were recorded sequentially by varying weight ratios. The monotonic blue shifting of the absorption peak position indicated the interaction between donor and acceptor materials. The possibility of electron transfer from donor (MEH-PPV) to acceptor (CuFeS2) was approved with photoluminescence analysis. Subsequently, we have fabricated a hybrid solar cell by incorporating CuFeS2 nanocomposite with MEH-PPV in open atmosphere and obtained 0.3% power conversion efficiency.

Time‐Resolved Studies of Energy Transfer in Thin Films of Green and Red Fluorescent Proteins

AbstractBiologically derived fluorescent proteins are attractive candidates for lasing and sensing due to their excellent optical properties, including their high quantum yield, spectral tunability, and robustness against concentration quenching. Here, a time‐resolved study of the fluorescence dynamics of protein thin films is reported for the enhanced green fluorescent protein (EGFP), the red‐emitting tandem‐dimer protein tdTomato, and blends of EGFP and tdTomato. The exciton dynamics are characterized by using spectrally and time‐resolved measurements of fluorescence and a threefold reduction in lifetime is observed when going from solution to thin film, down to 1 and 0.6 ns for EGFP and tdTomato, respectively. This finding is attributed to a dipole–dipole nonradiative Förster resonant energy transfer (FRET) in solid state. The temporal characteristics of FRET in blended thin films are also studied and increased nonradiative transfer rates are found. Finally, efficient sensitization of a semiconductor surface with a protein thin film is reported. Such a configuration may have important implications for energy harvesting in hybrid organic–inorganic solar cells and other hybrid optoelectronic devices.

High Efficiency (>17%) Si‐Organic Hybrid Solar Cells by Simultaneous Structural, Electrical, and Interfacial Engineering via Low‐Temperature Processes

AbstractHighly efficient organic–inorganic hybrid solar cells of Si‐poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) have been demonstrated by simultaneous structural, electrical, and interfacial engineering with low processing temperature. Si substrate has been sculpted into hierarchical structure to reduce light reflection loss and increase interfacial junction area at the same time. Regarding the electrical optimization, highly conductive organic PEDOT:PSS layer has been formulated with low sheet resistance. It is argued that the sheet resistance, rather than conductivity, is the primary parameter for the high efficiency hybrid cells, which leads to the optimization of thickness, i.e., thick enough to have low sheet resistance but transparent enough to pass the incident sunlight. Finally, siloxane oligomers have been inserted into top/bottom interfaces by contact‐printing at room ambient, which suppresses carrier recombination at interfaces and reduces contact resistance at bottom electrode. Contrary to high‐temperature doping (for the formation of front surface or back surface fields), wet solution processes or vacuum‐based deposition, the contact‐printing can be done at room ambient to reduce carrier recombination at the interfaces. The high efficiency obtained with low processing temperature can make this type of cells be a possible candidate for post‐Si photovoltaics.

Planar n-Si/PEDOT:PSS hybrid heterojunction solar cells utilizing functionalized carbon nanoparticles synthesized via simple pyrolysis route

Herein, we present a facile and simple strategy for in situ synthesis of functionalized carbon nanoparticles (CNPs) via direct pyrolysis of ethylenediaminetetraacetic acid (EDTA) on silicon surface. The CNPs were incorporated in hybrid planar n-Si and poly(3,4-etyhlenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solar cells to improve device performance. We demonstrate that the CNPs-incorporated devices showed increased electrical conductivity (reduced series resistance) and minority carrier lifetime (better charge carrier collection) than those of the cells without CNPs due to the existence of electrically conductive sp2-hybridized carbon at the heterojunction interfaces. With an optimal concentration of CNPs, the hybrid solar cells exhibited power conversion efficiency up to 11.95%, with an open-circuit voltage of 614 mV, short-circuit current density of 26.34 mA cm−2, and fill factor of 73.93%. These results indicate that our approach is promising for the development of highly efficient organic–inorganic hybrid solar cells.

On the light-induced enhancement in photovoltaic performance of PEDOT:PSS/Si organic-inorganic hybrid solar cells

Light-induced degradation has been identified to be a critical issue for most silicon-based solar cell technologies. This study presents an observation of an opposite light-induced enhancement (LIE) effect in photovoltaic performance in poly(3,4-ethylthiophene):polystyrenesulfonate/n-Si organic-inorganic hybrid solar cells. The reduced density of interface states under light soaking (LS) is found to be responsible for the LIE of the hybrid solar cells. An increased minor carrier lifetime under LS and a switchable photoluminescence intensity while applying a voltage bias are observed, providing evidence for the underlying physical mechanism.

Zr-doped TiO2 as a thermostabilizer in plasmon-enhanced dye-sensitized solar cells

Harvesting solar energy is a promising solution toward meeting the world’s ever-growing energy demand. Dye-sensitized solar cells (DSSCs) are hybrid organic–inorganic solar cells with tremendous potential for commercial application, but they are plagued by inefficiency due to their poor sunlight absorption. Plasmonic silver nanoparticles (AgNPs) have been shown to enhance the absorptive properties of DSSCs, but their plasmonic resonance can cause thermal damage resulting in cell deterioration. Hence, the influence of Zr-doped TiO2 on the efficiency of plasmon-enhanced DSSCs was studied, showing that 5 mol.% Zr-doping of the photoactive TiO2 material can improve the photovoltaic performance of DSSCs by 44%. By examining three different DSSC designs, it became clear that the efficiency enhancing effect of Zr strongly depends on the proximity of the Zr-doped material to the plasmonic AgNPs.

Electrical Properties of Ultra-thin TiO2 Compact Layer on FTO for Perovskite Solar cells

A TiO2 compact layer or blocking layer plays a crucial role in a hybrid organic-inorganic lead halide perovskite solar cell because it can prevent the carrier recombination at the interface of fluorine-doped tin oxide (FTO) and perovskite layers. There are several methods to fabricate this layer such as spray pyrolysis or spin-coating which is solution-based synthesis that is difficult to avoid pinholes in the surface of the blocking layer. In this work, TiO2 blocking layers are fabricated by radio-frequency (RF) magnetron sputtering using Ti metallic target with O2 partial pressure in Ar atmosphere on FTO coated glasses. The controlled parameters for the deposition of TiO2 compact layer are RF power, O2 partial pressure, and deposition time. The optimization of the TiO2 compact layers are found from the diode I-V characteristics between the TiO2/FTO interfaces. The resistance between the TiO2/FTO interfaces deviates from an ohmic contact towards a diode behavior when the thickness of TiO2 is increased. The thickness of the films is directly measured by surface profilometer. In addition, the UV-VIS-NIR spectroscopy is used to observe the optical transmission of the films.