High-efficiency Hybrid Solar Cells Research Articles

An Aggregation-Suppressed Polymer Blending Strategy Enables High-Performance Organic and Quantum Dot Hybrid Solar Cells.

Solution-processing hybrid solar cells with organics and colloidal quantum dots (CQDs) have drawn substantial attention in the past decade. Nevertheless, hybrid solar cells based on the recently developed directly synthesized CQD inks are still unexplored. Herein, a facile polymer blending strategy is put forward to enable directly synthesized CQD/polymer hybrid solar cells with a champion efficiency of 13%, taking advantage of the conjugated polymer blends with finely optimized aggregation behaviors. The spectroscopic and electrical investigations on carrier transport and recombination indicate that polymer blends can endow fast carrier transport and less recombination over the single counterparts. Moreover, the blending strategy offers a "dilution effect" for top-notch photovoltaic polymers with excessively strong aggregation tendency, resulting in moderate feature domain size and surface roughness, which afford fast hole transport and therefore high photovoltaic performance. The effectiveness of this strategy is successfully validated using two pairs of photovoltaic polymers. Accordingly, the relationships between polymer morphology, carrier transport, and photovoltaic performance are established to advance the progress of CQD/polymer hybrid solar cells. Such progress stresses that the utilization of aggregation-suppressed polymer blends is a facile approach toward the fabrication of high-efficiency organic-inorganic hybrid solar cells.

Encapsulation of poly(m-aminobenzodioxol)-Fe3O4 superparamagnetic nanorods and iron (III) thiocyanate complex in hydrogel toward hybrid solar cells

In this proof-of-concept study, a nanocomposite of poly(m-aminobenzodioxol) with Fe3O4 magnetic nanorods (PABD-Fe3O4NRs) was synthesized using a one-pot synthesis. The nanocomposite was characterized using transmission electron microscopy (TEM), environmental scanning electron microscopy (ESEM), and Fourier-transform infrared spectroscopy (FT-IR), which all displayed successful synthesis. The PABD-Fe3O4NRs were then incorporated within a graphite-implanted polyacrylamide (PAA-G) hydrogel matrix to develop an innovative nanocomposite-polymer solar cell. The additional Fe3+ was then used to form a metal thiocyanate complex, [FeSCN]2+, within the pores of the hydrogel. To the best of our knowledge, this study is the first to report the use of a conductive hydrogel nanocomposite for the encapsulation of the active layer within a hybrid solar cell. The incorporation of this material as a single layer enabled storage of the [FeSCN]2+ solution as well as increased the formation of interconnected channels for faster electron transfer and diminished charge transfer resistance, and therefore, significantly enhanced the overall efficiency of the solar cell. Under simulated solar irradiation, the final FTO│TiO2 / PAA-G-PABD-Fe3O4NRs gel [FeSCN]2+ │Al solar cell demonstrated a power conversion efficiency (PCE or η) of 6.08% and a significant enhancement of 2100% in comparison with the solar cells fabricated with PABD-Fe3O4NRs in the absence of the PAA-G and [FeSCN]2+ complex. Our preliminary results exhibited high thermal stability and displayed superior photovoltaic properties when compared to other similar solar cells in literature. We envisage that the synthesis of hydrogel nanocomposites using various nanomaterials will significantly enhance the development of high-efficiency hybrid solar cells.

Efficiency enhancement of Si nanostructure hybrid solar cells by optimizing non-radiative energy transfer from Si quantum dots

Non-radiative energy transfer (NRET) from silicon quantum dots (SiQDs) terminated with ligands is an effective way to improve solar cell efficiency. The NRET effect can be enhanced by minimizing the distance between SiQDs and the solar cell surface. SiQDs were inserted between poly (3,4-ethylene dioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) and Si nanostructures of hybrid heterojunction solar cells. To clarify dependence on ligand length, three different ligands of different lengths were investigated. 1-octene, which has the shortest ligand length, showed the greatest enhancement of NRET, resulting in the highest solar cell efficiency. The non-radiative energy transfer (NRET) effect in Si quantum dots (SiQDs) can be enhanced by shortening the ligand length, resulting in enhanced short circuit current, thus significantly improving the energy conversion efficiency of solar cells. • High-efficiency hybrid solar cells were fabricated by inserting SiQDs into hybrid solar cell with Si nanotips and PEDOT:PSS. • Non-radiative energy transfer from SiQDs terminated with ligands effectively enhanced conversion efficiency of solar cells. • SiQDs with shorter ligands had a higher conversion efficiency. • The highest conversion efficiency of 12.4% was given by hybrid solar cells with 1-octene terminated SiQDs.

Enhanced Photovoltaic Performance of Hybrid Solar Cells with a Calcium Interfacial Metal Electrode

A better understanding of how the interfacial layer influences charge carrier recombination would benefit the development of high-efficiency hybrid solar cells (HSCs). HSCs based on poly(3-hexylthiophene) (P3HT)/Si nanoparticles (Si NPs) with three identical electrodes were used as reference system to investigate the interfacial layer effects on device performance. The standard solar-grade silicon was produced using rice husk ash (RHA) as a biogenic source. The RHA was purified by using a low-cost and simple method followed by modified magnesiothermic reduction reaction to produce crystalline Si NPs. Prepared Si NPs as an acceptor material with different percentages of Ca interface layer metal electrodes on HSCs were studied. A highly conductive electrode was one of the important factors for enhancing the fill factor and power conversion efficiency (PCE). For fabrication and characterization of P3HT/Si NP HSCs with three identical thermally evaporated electrodes, Al (100 nm), Ca/Al (10 nm/90 nm), and Ca/Al (20 nm/80 nm) were used as top electrode. The device with a Ca/Al (10 nm/90 nm) electrode exhibited a lower recombination, while its efficiency was 20% and 10% higher than the devices with the Al (100 nm) and Ca/Al (20 nm/80 nm) electrodes, respectively.

Modeling of High-Efficiency Multi-Junction Polymer and Hybrid Solar Cells to Absorb Infrared Light.

In this paper, we present our work on high-efficiency multi-junction polymer and hybrid solar cells. The transfer matrix method is used for optical modeling of an organic solar cell, which was inspired by the McGehee Group in Stanford University. The software simulation calculates the optimal thicknesses of the active layers to provide the best short circuit current (JSC) value. First, we show three designs of multi-junction polymer solar cells, which can absorb sunlight beyond the 1000 nm wavelengths. Then we present a novel high-efficiency hybrid (organic and inorganic) solar cell, which can absorb the sunlight with a wavelength beyond 2500 nm. Approximately 12% efficiency was obtained for the multi-junction polymer solar cell and 20% efficiency was obtained from every two-, three- and four-junction hybrid solar cell under 1 sun AM1.5 illumination.

Improved device performance stability of bulk-heterojunction hybrid solar cells with low molecular weight PCPDPTB

The molecular weight effect of low band-gap conjugated polymer, poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)], PCPDTBT, with an optical energy gap of Eg ∼1.4eV, on the device stability of quantum dot polymer hybrid solar cells has been studied. The PCPDTBT is integrated into hybrid polymer/QDs solar cells, where PCPDTBT acts as electron donor and CdSe QDs as electron acceptor. Morphology investigation and results on device performance over time indicate that low molecular weight PCPDTBT is preferable to fabricate high efficiency hybrid solar cells with long-term stability. An average power conversion efficiency of 2% was measured for PCPDTBT-CdSe QD devices with a molecular weight of <12kDa. The long-term stability of the photovoltaic performance of the devices was investigated and found superior compared to devices with PCPDTBT of higher molecular weight. About 96% of the PCE remained after a week of storage of solar cell devices without any further encapsulation in a glove-box. It is assumed that the improvement is mainly due to the better distribution of CdSe QDs within the polymer matrix of low molecular weight PCPDTBT in hybrid solar cells and an improved preservation of the nanomorphology of the hybrid film over time.

Low-Pressure-Assisted Coating Method To Improve Interface between PEDOT:PSS and Silicon Nanotips for High-Efficiency Organic/Inorganic Hybrid Solar Cells via Solution Process.

PSS) on nanostructures. Here we demonstrate low-pressure-assisted coating method of PSS on surface-modified silicon nanotips with broadband light-trapping characteristics to improve interface property and to achieve high-efficiency hybrid solar cells through a solution process. The approach enhances the effective minority-carrier lifetime and the coverage of PSS on the surface of nanostructures. Hybrid solar cells fabricated with surface-modified nanotips exhibit a high fill factor of 70.94%, short-circuit current density of 35.36 mA/cm(2), open-circuit voltage of 0.528 V, and power conversion efficiency of 13.36%. The high efficiency and the high fill factor are achieved because of conformal coating of PSS via a low-pressure-assisted coating process, excellent light harvesting without sacrificing the minority-carrier lifetime, and efficient charge separation/collection of photogenerated carriers.

High-efficiency aqueous-processed hybrid solar cells with an enormous Herschel infrared contribution.

Aqueous-processed solar cells have evolved into a new generation of promising and renewable energy materials due to their excellent optical, electrical, and low-cost properties. In this work, Cd0.75Hg0.25Te colloid quantum dots (CQDs) were incorporated into a water-soluble conjugated polymer with broad absorption and high charge-carrier-mobility (5 × 10(-4) cm(2) V(-1) s(-1)) to obtain a composite with an absorption spectrum ranging from 300 to 1200 nm. The matched energy level between polymer and CQDs ensured the effective electron transfer, while the interpenetrating network structure formed via heat treatment guaranteed the quick electron transport. Moreover, the formation process of the interpenetrating network was systematically monitored by using AFM and TEM instruments and further confirmed through the measurement of charge-carrier-mobility of the active layers. In combination with the surface modification of a single Cd0.75Hg0.25Te layer, this aqueous-processed solar cell showed excellent photovoltaic response and the power conversion efficiency (PCE) reached 2.7% under AM 1.5 G illumination (100 mW cm(-2)). Especially, the contribution of the Herschel infrared region (780-1100 nm) to the photocurrent was as high as 15.04%. This device showed the highest PCE among organic-inorganic hybrid solar cells (HSCs) based on CdxHg1-xTe CQDs and the highest near infrared (NIR) contribution among aqueous-processed HSCs, indicating the enormous potential of taking advantage of NIR energy in a solar spectrum and a promising application in solar cells especially used in cloudy weather.

Multi-branched CdSe nanocrystals stabilized by weak ligand for hybrid solar cell application.

In this article, multi-branched CdSe nanocrystals were produced by a facile colloidal approach stabilized by oleylamine at a relative low temperature. The as-prepared multi-branched CdSe nanocrystals after simple washing process were used in the fabrication of poly(3-hexylthiophene)/CdSe bulk heterojunction photovoltaic device. The effective charge separation in the poly(3-hexylthiophene)/ CdSe nanocomposites have been confirmed by the strong photoluminescence quenching. The films of the blends of P3HT and simply-washed CdSe nanocrystals show more uniform morphology and flatter surface than the film of the bends of P3HT and pyridine-refluxed CdSe nanocrystals. The corresponding power conversion efficiency under 1 sun is about 0.66% for the P3HT/pyridine-washed CdSe hybrid device. Our work did a preliminary study in the hybrid solar cell application of branched blenze CdSe nanocrystals prepared by an easier way, and will be interesting and helpful for making the high-efficiency hybrid solar cells with branched CdSe acceptors.

High efficiency silicon nanohole/organic heterojunction hybrid solar cell

High efficiency hybrid solar cells are fabricated based on silicon with a nanohole (SiNH) structure and poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). The SiNH structure is fabricated using electroless chemical etching with silver catalyst, and the heterojunction is formed by spin coating of PEDOT on the SiNH. The hybrid cells are optimized by varying the hole depth, and a maximum power conversion efficiency of 8.3% is achieved with a hole depth of 1 μm. The SiNH hybrid solar cell exhibits a strong antireflection and light trapping property attributed to the sub-wavelength dimension of the SiNH structure.

High-efficiency hybrid solar cells by nanostructural modification in PEDOT:PSS with co-solvent addition

Conducting polymer poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) is gaining technological importance for the fabrication of organic and organic–inorganic heterostructure devices. The conductivity of PEDOT:PSS can be improved by the addition of co-solvents. Here, we show that the simple addition of a suitable wt% of a co-solvent, either ethylene glycol (EG) or dimethyl sulfoxide (DMSO), in PEDOT:PSS can significantly enhance the performance of hybrid solar cells. We provide a morphological model to explain the influence of the co-solvents in PEDOT:PSS, in which the co-solvent modifies the internal crystalline ordering of individual PEDOT nanocrystals that increases the crystal size and forms closely packed nanocrystals, and it also facilitates rearrangement of PSS that reduces its surface chain networks to enhance the polymer conductivity and hybrid solar cell properties. A hybrid solar cell made of EG 7 wt% modified PEDOT:PSS on planar Si exhibits an exceptionally high power conversion efficiency exceeding 12% for the first time.

Highly efficient poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/Si hybrid solar cells with imprinted nanopyramid structures

High-efficiency hybrid solar cells based on nanostructured silicon and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), which were fabricated via a simple nanoimprint fabrication process, demonstrated an excellent power conversion efficiency of 10.86%. The complex and costly high-temperature photolithography and masking steps were replaced by techniques that are low-cost and capable of mass production. The nanopyramid structures fabricated on the silicon surface provided an antireflective effect and have a radial junction architecture that enhanced the light absorption and carrier collection efficiency. The short-circuit current density (Jsc) of the hybrid solar cell with nanopyramid structures was greatly improved from 24.5 mA/cm2 to 32.5 mA/cm2 compared with that of a flat surface device. The highest solar cell efficiency was achieved on a 525 μm-thick 2.3 Ω cm n-type Czochralski process (CZ) Si substrate with a designated area of 4 cm2.

Protic Ionic Liquids as p-Dopant for Organic Hole Transporting Materials and Their Application in High Efficiency Hybrid Solar Cells

Chemical doping is a powerful method to improve the charge transport and to control the conductivity in organic semiconductors (OSs) for a wide range of electronic devices. We demonstrate protic ionic liquids (PILs) as effective p-dopant in both polymeric and small molecule OSs. In particular, we show that PILs promote single electron oxidation, which increases the hole concentration in the semiconducting film. The illustrated PIL-doping mechanism is compatible with materials processed by solution and is stable in air. We report the use of PIL-doping in hybrid solar cells based on triarylamine hole transporting materials, such as 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9'-spirobifluorene (spiro-OMeTAD). We show improved power conversion efficiency by replacing lithium salts, typical p-dopants for spiro-OMeTAD, with PILs. We use photovoltage-photocurrent decay and photoinduced absorption spectroscopy to establish that significantly improved device performance is mainly due to reduced charge transport resistance in the hole-transporting layer, as potentiated by PIL-doping.

High Efficiency Solar Cells As Fabricated by Sb2S3-Modified TiO2 Nanofibrous Networks

High-efficiency hybrid solar cells (HSCs) based on electrospun titanium dioxide (TiO2) nanofibers plus poly(3-hexylthiophene) (P3HT) are fabricated by means of both the pretreatment using tetrahydrofuran (THF) vapor and the surface modification using n-type antimony chalcogenide (Sb2S3) on the TiO2 nanofibrous networks. It is revealed that the THF pretreatment not only reinforces the interfacial physical contact but also suppresses the interfacial recombination. The Sb2S3 modification improves the light absorption and charge transfer. Given that the active layer of the HSCs is as thin as 300 nm, it is demonstrated that the power conversion efficiency (PCE) is enhanced over 175%, exhibiting a PCE of 2.32%.

Optical and electrical effects of plasmonic nanoparticles in high-efficiency hybrid solar cells

Plasmonics have been proven to be an effective way to harness more incident light to achieve high efficiency in photovoltaic devices. Herein, we explore the possibility that plasmonics can be utilized to enhance light trapping and power conversion efficiency (PCE) for polymer-quantum dot (QD) hybrid solar cells (HSCs). Based on a low band-gap polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) and a CdSe QD bulk-heterojunction (BHJ) system, gold nanoparticles were doped at different locations of the devices. Successfully, an improved PCE of 3.20 ± 0.22% and 3.16 ± 0.15% was achieved by doping the hole transporting layer and the active layer, respectively, which are among the highest values reported for CdSe QD based HSCs. A detailed study of processing, characterization, microscopy, and device fabrication is conducted to understand the underlying mechanism for the enhanced device performance. The success of this work provides a simple and generally applicable approach to enhance light harnessing of polymer-QD hybrid solar cells.

Hybrid solution-processed bulk heterojunction solar cells based on bismuth sulfide nanocrystals

High efficiency organic and hybrid solar cells create demand for novel electron acceptor materials that possess appropriate energetic band levels and bandgap for efficient solar energy harnessing. We present hybrid bulk heterojunction devices based on P3HT and bismuth sulfide nanocrystals, a semiconductor based on environmentally friendly compounds, with a power conversion efficiency of 1% and NIR sensitization at 700 nm of 30%, among the highest ever reported for P3HT.

Enhanced Conversion Efficiency for Si Nanowire–Organic Hybrid Solar Cells through the Incorporation of Organic Small Molecule

We demonstrate high-efficiency hybrid solar cells based on heterojunctions formed between n-type silicon nanowires (SiNWs) and p-type organic semiconductors fabricated using a simple solution-based approach. Two types of devices have been fabricated with different organic materials used, namely poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and a small molecule, 2,2',7,7'-tetrakis(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (Spiro-OMeTAD). The cells are characterized and compared in terms of their physical characteristics and photovoltaic performance. Using SiNWs of the same length of 0.35 µm, it is found that the SiNWs/Spiro cells exhibit a power conversion efficiency of 10.3%, which is higher than the 7.7% of SiNWs/PEDOT cells. The results are interpreted in terms of the ability of the two organic semiconductors to fill the gaps between the SiNWs and the optical reflectance of the samples. The degradation of the SiNWs/Spiro cells is also studied and presented.

Si Nanowires Organic Semiconductor Hybrid Heterojunction Solar Cells Toward 10% Efficiency

High-efficiency hybrid solar cells are fabricated using a simple approach of spin coating a transparent hole transporting organic small molecule, 2,2',7,7'-Tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (Spiro-OMeTAD) on silicon nanowires (SiNWs) arrays prepared by electroless chemical etching. The characteristics of the hybrid cells are investigated as a function of SiNWs length from 0.15 to 5 μm. A maximum average power conversion efficiency of 9.92% has been achieved from 0.35 μm length SiNWs cells, despite a 12% shadowing loss and the absence of antireflective coating and back surface field enhancement. It is found that enhanced aggregations in longer SiNWs limit the cell performance due to increased series resistance and higher carrier recombination in the shorter wavelength region. The effects of the Si substrate doping concentrations on the performance of the cells are also investigated. Cells with higher substrate doping concentration exhibit a significant drop in the incident photons-to-current conversion efficiency (IPCE) in the near infrared region. Nevertheless, a promising short circuit current density of 19 mA/cm(2) and IPCE peak of 57% have been achieved for a 0.9 μm length SiNWs cell fabricated on a highly doped substrate with a minority-carrier diffusion length of only 15 μm. The results suggest that such hybrid cells can potentially be realized using Si thin films instead of bulk substrates. This is promising towards realizing low-cost and high-efficiency SiNWs/organic hybrid solar cells.

High efficiency hybrid solar cells using post-deposition ligand exchange by monothiols

High-performance hybrid solar cells (HSCs) based on P3HT : CdSe QD blends are achieved through post-deposition ligand exchange by n-butanethiol (n-BT) with a high power conversion efficiency of 3.09%. The mechanism by which n-BT modifies the surface structures of CdSe QDs and thus improves the HSCs performance is investigated.

Simple Approach of Fabricating High Efficiency Si Nanowire/Conductive Polymer Hybrid Solar Cells

We present a simple approach of fabricating high-efficiency hybrid solar cells based on silicon nanowires (SiNWs) and a conductive polymer, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). PEDOT:PSS is directly spin coated on vertical SiNW arrays fabricated by electroless chemical etching to form a core-sheath heterojunction. A silver grid is used as the top anode. Compared to a planar Si/PEDOT:PSS cell, the power conversion efficiency of a 1-cm2 SiNW/PEDOT:PSS cell increases greatly from 6.2% to 9%. Cells with different SiNW lengths are also studied, and it is found that enhanced aggregation of longer SiNWs leads to poor surface coverage by PEDOT and, hence, degraded solar cell characteristics.