Performance Of Hybrid Solar Cells Research Articles

Structural Design and Simple Posttreatment of the Hole Transport Layer to Improve Performance of Hybrid Solar Cells

The performance of organic‐inorganic hybrid solar cells (HSCs) can be improved by modifying the hole transport layer (HTL). Poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is the most active HTL material in organic‐inorganic HSCs and has been widely studied. Nevertheless, charge transfer in PEDOT:PSS is limited and inefficient due to the presence of the weak ionic conductor PSS. Moreover, the working function of the PEDOT:PSS film and the passivation of the PSS at the Si/PEDOT:PSS interface play a crucial role in carrier separation. The focus of this work is to explore a universal modification method to simultaneously achieve improved charge transport and interfacial passivation capability when using PEDOT:PSS as HTL. By combining bilayer design and simple solution posttreatment, the direct current conductivity (σdc) and work function of the HTL based on PEDOT:PSS are increased to 765 S cm−1 and 5.00 eV, respectively. The organic‐inorganic HSCs prepared using this approach achieve a photovoltaic conversion efficiency (PCE) of 12.33%, achieving a 16.54% improvement over untreated devices.

Studying the impact of Mg doping on the physical properties of CdS nanocrystals for the fabrication of hybrid solar cells–based organic P3HT : PCBM polymers and inorganic Mg‐doped CdS nanocrystals

Herein, the influence of Mg-doped CdS nanocrystals (NCs) on the performance of hybrid solar cells (HSCs) is investigated for the first time. Pristine and Mg-doped CdS NCs at different concentrations (0.25, 0.5, and 0.75 mol%) are synthesized using the heating up method. The effect of Mg on structural, compositional, morphological, optical, and electrical properties of CdS NCs is examined. The structural analysis showed a peak shift toward a higher wavelength, while lattice parameters a and c are decreased. As the Mg concentration increases, the shape and size of the CdS NCs are considerably changed, while the bandgap is tuned from 2.66 to 2.44 eV. Besides, the resistivity of CdS is significantly decreased while carrier concentration increases. Then, the device is fabricated with a configuration of FTO/TiO2/P3HT:PC61BM/MoO3/Ag, wherein the influence of different concentrations of undoped and Mg-doped CdS NCs on the performance of HSCs is explored. The Mg-doped CdS NCs exhibited a power conversion efficiency of 2.92%, 2.5 times higher than the polymer device. Thus, the results revealed that the Mg doping significantly improved the properties of CdS NCs and the performance of HSCs. Henceforth, this work would provide a new path to enhance the power conversion efficiency of the HSCs in a low-cost approach.

Performance enhancement through optimization of metal oxide electron transport layer in hybrid solar cell

This work deals with analysis and optimization of PEDOT:PSS-Si-SnO2 hybrid solar cell performance. The effect of interface defect and temperature on such device are analysed and calibrated with the experimental work in the literature. The performance of such solar cell is boosted using SnO2 as back side electron bypass layer and considerable optimization is done. The outcome of this work indicates suitable range for electron affinity of such bypass layer within 3.9 eV to 4.7 eV. Beyond these, the interface recombination current limits the open circuit voltage and efficiency is degraded. The energetic position of the interface defect state at the Si-SnO2 also affects the efficiency in such device. Moreover, allowed work function of back contact material for optimum performance in such device finds in the range 4 eV to 4.7 eV.

Mitigating the charge trapping effects of D-sorbitol/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) polymer blend contacts to crystalline silicon

Abstract Solution-processable conductive polymers are advantageous materials for making inexpensive, electrical junctions to crystalline semiconductors. We have investigated methods to improve the device performance of hybrid solar cells made from n-type silicon and a conductive polymer glue based on a blend of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and D-sorbitol. The PEDOT:PSS blend behaves like a high work function metal creating a Schottky-type junction. The addition of D-sorbitol increases PEDOT:PSS conductivity and provides adhesive properties, allowing the top contact of the solar cell to be laminated onto the silicon substrate. Unfortunately, the addition of the D-sorbitol to the PEDOT:PSS significantly alters the shape of the measured current-voltage performance curve of a crystalline silicon (n-Si)/PEDOT:PSS junction. Under illumination, this results in a decline in the fill factor (FF) and a drop in photocurrent density (J sc) compared to PEDOT:PSS-only devices. We have discovered that the decline in device performance is likely due to surface trap states caused by D-sorbitol/silicon interaction and/or silicon oxidation. X-ray photoelectron spectroscopic (XPS) analysis shows that surface oxidation quickens, and possible silicon surface functionalization with D-sorbitol occurs while processing the D-sorbitol/PEDOT:PSS contact on H-terminated surfaces. To overcome these interface issues, the silicon surface was chemically modified using surface methylation, making it insensitive to D-sorbitol/silicon interactions and surface oxidation during the processing of the PEDOT:PSS polymer blend contact. This also enabled the crystalline silicon (n-Si)/s-PEDOT:PSS device performance to be maintained for longer periods. Using a silicon surface methylation strategy, good device performance could be achieved without changing the adhesive properties of D-sorbitol/PEDOT:PSS polymer blend.

Hybrid Perovskite Quantum Dot/Non‐Fullerene Molecule Solar Cells with Efficiency Over 15%

AbstractOrganic‐inorganic hybrid film using conjugated materials and quantum dots (QDs) are of great interest for solution‐processed optoelectronic devices, including photovoltaics (PVs). However, it is still challenging to fabricate conductive hybrid films to maximize their PV performance. Herein, for the first time, superior PV performance of hybrid solar cells consisting of CsPbI3 perovskite QDs and Y6 series non‐fullerene molecules is demonstrated and further highlights their importance on hybrid device design. In specific, a hybrid active layer is developed using CsPbI3 QDs and non‐fullerene molecules, enabling a type‐II energy alignment for efficient charge transfer and extraction. Additionally, the non‐fullerene molecules can well passivate the QDs, reducing surface defects and energetic disorder. The champion CsPbI3 QD/Y6‐F hybrid device has a record‐high efficiency of 15.05% for QD/organic hybrid PV devices, paving a new way to construct solution‐processable hybrid film for efficient optoelectronic devices.

Exploring the performance of hybrid solar cells based on organic polymers/inorganic CdS nanostructures

Herein, different shapes of CdS nanostructures such as irregular, spherical nanoparticles (NPs) and nanorods (NRs) are reported using facile heating up method by tuning the solvent ratio between oleic acid and oleylamine. This is the first report deals with the synthesis of CdS NRs at relatively low reaction temperature as well as investigating the effect of different shapes of CdS on the hybrid solar cells (HSCs) performance. From the structural analysis, a hexagonal crystal structure of CdS is observed. The optical analysis exhibits absorption in the visible region and the calculated bandgap is found to be 2.52 eV. The irregular and agglomerated CdS NPs showed inferior power conversion efficiency (PCE) while CdS NRs have demonstrated maximum PCE of 2.42% in comparison with the standard device. Thus, the research outcomes strongly highlight the impact of various CdS nanostructures on the HSCs performance and open-up new avenue to accomplish the utmost PCE of HSCs in low-cost approach.

Binary-Structured Si Surface Modification by an Alkaline Treatment: Application to Poly(3,4-Ethylenedioxythiophene)-Poly(Styrene Sulfonate)/Silicon Heterojunction Solar Cells

In recent years, silicon-organic hybrid solar cells have attracted tremendous research attention owing to their low production cost and high performance. In the present work, tapered silicon nanowires (TSiNWs) were synthesized on random micro-pyramids (RM pyramids). On this binary structure, a poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) polymer was spin-coated. The tapering of SiNWs was performed by immersing the samples in NaOH solution. It was found that the tapering time affects significantly the reflectivity, the minority carriers lifetime and the coverage rate of Si surface by the PEDOT:PSS film. Indeed, an optimal tapering time of 6 s was determined. This time was sufficient to good incident light trapping and to reduce the surface defects. This simple and low-cost surface structuring technique holds high potential for improving the performance of hybrid solar cells with large junction area.

Recent advances in highly efficient organic-silicon hybrid solar cells

Organic-silicon hybrid solar cells (organic/Si HSCs) have drawn much attention in the development of modern low-cost photovoltaic solar cells. Due to simpler and less expensive fabrication processes at room temperature, the HSCs have many superiorities over conventional silicon solar cells, positioning the HSCs be a striking research topic. Recently, a significant amount of research has been done to improve the yield and efficiency of hybrid solar cells. The performance enhancement of hybrid solar cells highly depends on a combination of the electrical, optical, materials and structural aspects. This review is dedicated to the recent advances in the mechanism, fabrication processes and light management in organic/Si HSCs, highlighting the important device structures, the surface texturing, the transparent electrodes as well as the integration of metallic nanostructures to improve the performances of hybrid solar cells.

Effects of interfacial ligand type on hybrid P3HT:CdSe quantum dot solar cell device parameters

A series of CdSe quantum dot acceptors possessing six different ligand frameworks (i.e., pivalic acid, pyridine, butylamine, tert-butylthiol, thiophenol, and tetrahydrothiophene) were used as platforms for investigating the influence of quantum dot surface chemistry on the performance of hybrid poly(3-hexythiophene-2,5-diyl) (P3HT):CdSe quantum dot bulk heterojunction (BHJ) solar cells. We confirm that the device parameters used to evaluate solar cell performance are significantly influenced by the nature of the quantum dot surface ligand. The dependence of short circuit current density (JSC) on the CdSe ligand type was probed using ultrafast time-resolved photoluminescence (PL) measurements, and good correlations between the ligand-dependent trends in JSC and excited state lifetime were found, in which the P3HT:CdSe quantum dot BHJs with the shortest PL lifetimes possess the largest device current densities. The frontier energy levels of the quantum dot acceptors are significantly influenced by surface ligands, wherein the device open circuit potentials (VOC) were found to linearly correlate with the energy difference (ΔEDA) between the HOMO of the P3HT donor and the electrochemically determined LUMO of the CdSe quantum dot acceptors over a range of 220 mV. This work demonstrates the versatility of quantum dot ligand engineering for tuning the device parameters and performance of hybrid solar cells.

μSR Study with Light Irradiation of P3HT:ZnO Nanoparticles as Active Material of Hybrid Solar Cells

Recently, hybrid solar cell that consists of a combination of organic and inorganic materials offers promise in increasing efficiency. Combination of conjugated polymer of Poly (3-hexyl thiophene)/P3HT which has the highest hole mobility with inorganic materials which has high electron mobility, good physical and chemical stability of inorganic nanocrystals, shows a better performance of hybrid solar cells. We have conducted a measurement to investigate the charge carrier transport in active material of hybrid solar cells by using muon spin relaxation (μSR) with light irradiation. A bulk sample used in this study is hybrid organic-inorganic material consisting of regio-regular P3HT and ZnO nanoparticles. Longitudinal-field μSR measurements were performed in magnetic field ranging from 0 to 395 mT at temperature of 10 K, 15 K and 25 K. Based on μSR measurement with light irradiation, we found that for those temperatures, longitudinal field dependence of λ1 was proportional with C-H0.5 curve indicating three-dimensional inter-chain diffusion. We assume that light irradiation initiates the production of exciton that increases the number of charge carrier in the sample and transports not only along the chain of polymer (one-dimensional) but also perpendicular to other chain of polymer (three-dimensional). With light irradiation, the crossover temperature from one-dimensional to three-dimensional of regio-regular P3HT and ZnO nanoparticles bulk sample was obtained at lower temperature of 10 K compared to previous result at 25 K without light irradiation.

Fabrication and properties of P3HT: PCBM/Cu2SnSe3 (CTSe) nanocrystals based inverted hybrid solar cells

Thin film solar cells with ITO/ZnO/P3HT:PCM:CTSe NCs/Ag structure were fabricated employing a fast and cost-effective procedure using blended solution of P3HT:PCBM:CTSe NCs deposited by spin casting, followed by thermal annealing steps. The CTSe NCs are prepared via solvothermal method. An inverted architecture of device with structure ITO/ZnO/P3HT: PCBM:CTSe NCs/Ag have been fabricated with different concentration of CTSe NCs in poly(3-hexyle thiophene) (P3HT): [6,6]phenyl-C61-butyric-acid-methyl-ester (PCBM) matrix. The effect of CTSe NCs on the performance of hybrid solar cell with optimized blend ratio of P3HT:PCBM and CTSe NCs has been investigated for optimum power conversion. The charge carrier extraction and recombination at the interface of donor-acceptor material were studied using Electrochemical impedance spectroscopy (EIS) under dark condition. EIS study has demonstrated that the charge transfer rate was higher for the device having optimized wt% of CTSe NCs (10 wt%) in P3HT:PCBM active layer. A significant improvement in the device performances was observed on incorporation of CTSe NCs. The device exhibited open circuit voltage (Voc) of 0.475 V, short circuit current density (Jsc) of 6.95 mA/cm2, fill factor (FF) of 0.41 and power conversion efficiency (PCE) of 1.35%.

Tunable photoluminescence from interconnected graphene network with potential to enhance the efficiency of a hybrid Si nanowire solar cell

An interconnected graphene network (IGN) structure with excellent photoluminescence (PL) properties was synthesized using a one-pot microwave-assisted hydrothermal carbonization route. The material exhibited intense and excitation-wavelength dependent PL emission located mainly in the UV-blue light range (300-450 nm). The result demonstrates that graphene networks could also be included in the emerging class of tunable PL carbon nanomaterials. Furthermore, we have taken a first step towards their incorporation into solar cell devices by fabricating IGN/p-SiNWs radial heterojunctions using the versatile potentiostatic electrodeposition technique. The IGN modified p-SiNW solar cell showed the best performance with an overall enhancement of power conversion efficiency of 7.5 times higher than the reference cell. We emphasize that the structural and electronic characteristics of the as-prepared IGN combined with tapering effects are directly responsible for the tripled short circuit current density and 9% improvement of open circuit voltage with respect to the reference cell. Finally, we have demonstrated that the IGN successfully passivated the Si nanowires' surface using intensity modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS). These promising findings indicate that further IGN exploitation may help to gain efficiency in future energy conversion applications.

A scanning probe microscopy study of nanostructured TiO2/poly(3-hexylthiophene) hybrid heterojunctions for photovoltaic applications.

The nanoscale morphology of photoactive hybrid heterojunctions plays a key role in the performances of hybrid solar cells. In this work, the heterojunctions consist of a nanocolumnar TiO2 surface covalently grafted with a monolayer of poly(3-hexylthiophene) (P3HT) functionalized with carboxylic groups (–COOH). Through a joint analysis of the photovoltaic properties at the nanoscale by photoconductive-AFM (PC-AFM) and surface photovoltage imaging, we investigated the physical mechanisms taking place locally during the photovoltaic process and the correlation to the nanoscale morphology. A down-shift of the vacuum level of the TiO2 surface upon grafting was measured by Kelvin probe force microscopy (KPFM), evidencing the formation of a dipole at the TiO2/P3HT-COOH interface. Upon in situ illumination, a positive photovoltage was observed as a result of the accumulation of photogenerated holes in the P3HT layer. A positive photocurrent was recorded in PC-AFM measurements, whose spatial mapping was interpreted consistently with the corresponding KPFM analysis, offering a correlated analysis of interest from both a theoretical and material design perspective.

Wet Imprinting of Channel-Type Superstructures in Nanostructured Titania Thin Films at Low Temperatures for Hybrid Solar Cells.

Hierarchically structured titania films, exhibiting interconnected foam-like nanostructures and large-scale channel-type superstructures, were achieved in an energy-saving way at low temperatures by a polymer template-assisted sol-gel synthesis in combination with a wet-imprinting process. The surface morphology was probed with scanning electron microscopy and atomic force microscopy, whereas the inner morphology was characterized with grazing incidence small-angle X-ray scattering measurements. Compared to the initial hybrid films, the titania films showed reduced structure sizes caused by removal of the polymer template. UV/Vis measurements showed an additional light-scattering effect at various angles of light incidence in the hierarchically structured titania films, which resulted in higher light absorption in the wet-imprinted active layer. To give proof of viability, the titania films were evaluated as photoanodes for dye-free hybrid solar cells. The dye-free layout allowed for low-cost fabrication, avoided problems related to dye bleaching, and was a more environmentally friendly alternative to using dyes. Under different angles of light incidence, the enhancement in the short-circuit current density was in good agreement with the improvement in light absorption in the superstructured active layer, demonstrating a positive impact of the superstructures on the photovoltaic performance of hybrid solar cells.

Enhanced Performance of Nanoporous Titanium Dioxide Solar Cells Using Cadmium Sulfide and Poly(3-hexylthiophene) Co-Sensitizers.

This work reports the effect of co-sensitization of nanoporous titanium dioxide using Cadmium Sulfide (CdS) and poly(3-hexylthiophene) (P3HT) on the performance of hybrid solar cells. CdS nanolayer with different thicknesses was grown on Titanium Dioxide (TiO2) nanoparticles by chemical bath deposition technique with varying deposition times. Both atomic force microscopy (AFM) and UV–Vis–NIR spectroscopy measurements of TiO2 electrode sensitized with and without CdS layer confirm that the existence of CdS layer on TiO2 nanoparticles. AFM images of CdS-coated TiO2 nanoparticles show that the surface roughness of the TiO2 nanoparticle samples decreases with increasing CdS deposition times. Current density–voltage and external quantum efficiency (EQE) measurements were carried out for corresponding solar cells. Both short circuit current density (JSC) and fill factor were optimized at the CdS deposition time of 12 min. On the other hand, a steady and continuous increment in the open circuit voltage (VOC) was observed with increasing CdS deposition time and increased up to 0.81 V when the deposition time was 24 min. This may be attributed to the increased gradual separation of P3HT and TiO2 phases and their isolation at the interfaces. The higher VOC of 0.81 V was due to the higher built-in voltage at the CdS–P3HT interface when compared to that at the TiO2–P3HT interface. Optimized nanoporous TiO2 solar cells with CdS and P3HT co-sensitizers showed external quantum efficiency (EQE) of over 40% and 80% at the wavelengths corresponding to strong absorption of the polymer and CdS, respectively. The cells showed an overall average efficiency of over 2.4% under the illumination of 70 mW/cm2 at AM 1.5 condition.

Effect of Au nanoparticles on the performance of hybrid solar cells

Recently, organic/inorganic hybrid solar cells have been extensively studied as a means to fabricate low-cost, relatively high efficiency solar cell devices. Along this line of research, we report the observed enhancement in the power conversion efficiency of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) on planar silicon (Si) hybrid heterojunction solar cell devices when incorporating gold (Au) nanoclusters in the PEDOT:PSS blend. The Au nanoclusters of size 3–5 nm were synthesized by wet chemical methods, and capped with 4-mercaptobenzoic acid (p-MBA). The power conversion efficiency (PCE) of the described structures with Au nanoclusters was measured to be 8.2%, which compares well to the PCE value of 7.3% for similar devices without the nanoclusters. The increased PCE of the devices is attributed to the measured increased electrical conductivity as well as near field plasmonic effects of the aforementioned films due to the incorporation of the Au nanoclusters, which is directly reflected in the improved fill factor and external quantum efficiency of the devices produced.

Enhancement of efficiency by embedding ZnS and Mn-doped ZnS nanoparticles in P3HT:PCBM hybrid solid state solar cells

Zinc sulphide (ZnS) and Mn-doped ZnS nanoparticles were synthesized by wet chemical method. The synthesized nanoparticles were characterized by UV-visible, fluorescence, X-ray diffraction (XRD), fourier transform infra-red (FTIR) spectrometer, field emission scanning electron microscope (FESEM) and high resolution transmission electron microscope (HRTEM). Scanning electron microscope (SEM) was used to find particle size while chemical composition of the synthesized materials was investigated by EDAX. UV-visible absorption spectrum of Mn-doped ZnS was slightly shifted to lower wavelength with respect to the un-doped zinc sulphide with decrease in the size of nanoparticles. Consequently, the band gap was tuned from 3.04 to 3.13 eV. The photoluminescence (PL) emission positioned at 597 nm was ascribed to 4 T 1 → 6 A 1 transition within the 3 d shell of Mn 2+ . X-ray diffraction (XRD) analysis revealed that the synthesized nanomaterials existed in cubic crystalline state. The effect of embedding un-doped and doped ZnS nanoparticles in the active layer and changing the ratio of PCBM ([6, 6]-phenyl-C61-butyric acid methyl ester) to nanoparticles on the performance of hybrid solar cell was studied. The device with active layer consisting of poly(3-hexylthiophene) (P3HT), [6, 6]-phenyl-C61-butyric acid methyl ester (PCBM), and un-doped ZnS nanoparticles combined in the ratio of (1:0.5:0.5) attained an efficiency of 2.42% which was found 71% higher than the reference device under the same conditions but not containing nanoparticles. Replacing ZnS nanoparticles with Mn-doped ZnS had a little effect on the enhancement of efficiency. The packing behavior and morphology of blend of nanoparticles with P3HT:PCBM were examined using atomic force microscope (AFM) and XRD.

Effect of thickness on the performance of hybrid solar cells fabricated using surfactant free lead sulfide quantum dots and poly(3-hexylthiophene-2,5-diyl) polymer

Surfactant free lead sulfide (PbS) nanoparticles (NPs) had been synthesized by precipitation method using lead acetate and thiourea as precursor. Mechanical grinding using mortar pestle has been done to deagglomerate the NPs to obtain finer nanoparticles. Ground NPs were further sonicated using high power probe sonicator in chlorobenzene solution. The poly(3-hexylthiophene-2,5-diyl) (P3HT) polymer was added into the chlorobenzene solution containing well dispersed PbS quantum dots (QDs). The blends solution containing PbS QDs and P3HT polymer was spin coated at different rotation per minute to obtain an optimum thickness for efficient hybrid solar cells fabrication. Scanning electron microscopy, atomic force microscopy and transmission electron microscopy analysis showed a homogeneous distribution of PbS QDs in the P3HT matrix. Photoluminescence (PL) measurements performed on the blends solution showed strong PL quenching, which was very much dependent on the PbS QDs concentration, indicating that proper photoinduced electron and hole transfer occurred in PbS:P3HT blend. Hybrid solar cells with configuration indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)/PbS:P3HT/Al had been fabricated with different active layer thicknesses. The device with optimum thickness showed the highest efficiency of 1.75% under Air Mass 1.5G illumination with the irradiation of 100mW/cm2. Morphological and optical investigations showed that improvement in the performance was achieved for the optimum thickness of the active layer due to good distribution and interconnection of surfactant free PbS QDs in P3HT matrix.

(Invited) Microplasmas Technologies for Engineering of Silicon Based Quantum Dot Solar Cells

Silicon nanocrystals (Si-ncs) are fascinating candidates for numerous applications such as photovoltaic cells. Solar cell technologies are highly dependent on silicon materials and Si-ncs with optimal energy band gap present potential for further development high efficiency solar cells. Especially, the tunability of the Si energy bandgap by precisely controlling the size of Si-ncs due to quantum confinement effects is expected to increase the efficiency of third generation all silicon tandem solar cells. Among the different semiconductor nanocrystals, Si-ncs have a special value as they are generally non-toxic and have been widely used on an industrial scale. A crucial aspect for Si-ncs integration into PV devices is represented by the control of the surface characteristics. Since quantum confinement effects are observed for small nanocrystal sizes (<10 nm in diameter) and at these dimensions the Si-nc surface chemistry plays a critical role for the overall optoelectronic properties and device performance. While the use of bulky and/or long molecular passivation is frequent and it is effective in stabilizing the Si-nc properties in colloids, it is highly detrimental for transport and device-related properties. In particular, photon absorption and subsequently exciton dissociation and carrier transport suffer from the separation between Si-ncs due to the bulky surfactants and considerably decrease the performance of devices. Recently, plasma-based approaches have been successfully applied to induce non-equilibrium chemical reactions on the surface of Si-ncs directly in colloids and to achieve surface-engineered Si-ncs without any bulky surfactants. Such approaches led to the enhancement of the Si-nc transport properties and its electronic interaction with a polymer matrix [1] as well as Si-nc long-term stability in water based solutions [2]. Another important issue is the doping of the Si-ncs. A number of issues especially regarding the large impurity formation energy by doping and transport are still in controversial debate. Doping of quantum confined Si-ncs offers unique opportunities to control the bandgap and the Fermi energy level. Particularly, boron-doped and phosphorus-doped quantum confined silicon nanocrystals (Si-ncs) are surface-engineered in colloidal solution by an atmospheric pressure radio frequency microplasma a will be underlined in this talk. In particular, we have performed the surface engineering of electrochemically etched p- and n-type Si-ncs where the no-change position of the dopant in Si-ncs is assured by room temperature processing [3]. We report on how the microplasma induced surface engineering can lead to drastically different outcomes due to different doping and how this impacts the corresponding optical and transport properties [3]. Next we report on Fermi level for doped Si-ncs. Our measurements demonstrate that surface engineering can tune the band energy levels and in particular the Fermi level. Indeed, we fabricate solar cells to test p-/n-type Si-ncs and induced surface chemistry to demonstrate the resulting effects. In particular it is noted that band alignment, dissociation efficiency and transport are all directly affected by the interplay of varying surface chemistry and doping levels. We demonstrate that surface chemistries induced on the Si-ncs strongly depend on the type of dopants and implications for third generation solar cells are discussed in details [4, 5]. As a final point, surfactant free microplasma surface-engineered Si-ncs can be integrated into the device architecture to be only optically active and provide a means of effective down-conversion of blue photons into red photons leading to 24% enhancement of the photocurrent under concentrated sunlight. We also show that the down-conversion effect under 1-sun is enhanced in the case of hybrid solar cells where microplasma engineered Si-ncs are also beneficial in the active absorption layer of the solar cells.

A comparative study on the performance of hybrid solar cells containing ZnSTe QDs in hole transporting layer and photoactive layer

In this paper, ZnSTe quantum dots-based hybrid solar cells (HSC) with two different device architectures have been investigated. The improved performance of the poly(3-hexylthiophene) (P3HT) and [6,6]phenyl C71 butyric acid methyl ester (PC71BM)-based bulk heterojunction (BHJ) solar cells by the incorporation of ZnSTe quantum dots (QDs) with an average size of 2.96 nm in PEDOT:PSS layer and active layer that have been demonstrated. Although the efficiency of both types of devices is almost the same, a close comparison reveals different reasons behind their improved performance. The device prepared with QDs in the HTL has shown reduced series resistance, increased shunt resistance, and improved mobility. On the other hand, QDs in the photoactive layer demonstrates increased photo-generation leading to improved efficiency.