Higher Jsc Research Articles

Improving the efficiency of organic sensitizers with various anchoring groups for solar energy applications

Acceptor electron groups play a key role in sensitizer proficiency in the DSSCs. To study this effect, a variety of acceptor electron groups were placed on a common scaffold. In this way, various intermediates and dyes were engineered, synthesized, purified and identified. Titanium dioxide and Na-doped TiO2 were employed to prepare of nanocrystalline layer of the photovoltaic devices. The blue movement was beholden in the UV–Visible test the coated photosensitizers on nanoparticle due to the J-type aggregation. To predict the usability of dyes in the structure of the solar cells, two methods, DFT and CV were employed. Finally, the DSSCs devices were prepared based on synthesized dyes and Na-doped TiO2 or TiO2. The photovoltaic device, which contains Dye 2, has the highest Jsc. The operation of photovoltaic device based on titanium dioxide is lower than that of Na-doped TiO2.

Novel Conjugated Polymers Containing 3-(2-Octyldodecyl)thieno[3,2-b]thiophene as a π-Bridge for Organic Photovoltaic Applications.

3-(2-Octyldodecyl)thieno[3,2-b]thiophen was successfully synthesized as a new π-bridge with a long branched side alkyl chain. Two donor-π-bridge-acceptor type copolymers were designed and synthesized by combining this π-bridge structure, a fluorinated benzothiadiazole acceptor unit, and a thiophene or thienothiophene donor unit, (PT-ODTTBT or PTT-ODTTBT respectively) through Stille polymerization. Inverted OPV devices with a structure of ITO/ZnO/polymer:PC71BM/MoO3/Ag were fabricated by spin-coating in ambient atmosphere or N2 within a glovebox to evaluate the photovoltaic performance of the synthesized polymers (effective active area: 0.09 cm2). The PTT-ODTTBT:PC71BM-based structure exhibited the highest organic photovoltaic (OPV) device performance, with a maximum power conversion efficiency (PCE) of 7.05 (6.88 ± 0.12)%, a high short-circuit current (Jsc) of 13.96 mA/cm2, and a fill factor (FF) of 66.94 (66.47 ± 0.63)%; whereas the PT-ODTTBT:PC71BM-based device achieved overall lower device performance. According to GIWAXS analysis, both neat and blend films of PTT-ODTTBT exhibited well-organized lamellar stacking, leading to a higher charge carrier mobility than that of PT-ODTTBT. Compared to PT-ODTTBT containing a thiophene donor unit, PTT-ODTTBT containing a thienothiophene donor unit exhibited higher crystallinity, preferential face-on orientation, and a bicontinuous interpenetrating network in the film, which are responsible for the improved OPV performance in terms of high Jsc, FF, and PCE.

Reactive ion etched, self-aligned, selective area poly-Si/SiO2 passivated contacts

Front/back poly-Si/SiO2 contact devices suffer from low short-circuit current density, Jsc, due to parasitic optical absorption in the front poly-Si layer. Thin poly-Si (~20 nm) allows for high Jsc but is not compatible with screen-printed fire-through contacts. We therefore study the effects of post-deposition etching of a thick poly-Si (200 nm) front layer by reactive ion etching (RIE) using the metal grid lines as a self-aligned mask. We show that passivation is maintained in the device during RIE and that Jsc is increased by a gain in the blue quantum efficiency response. However, our specific etching parameters cause non-uniform etching of the poly-Si leading to premature loss of passivation without optimal gain in Jsc. Etched, unpassivated layers can be re-passivated with a H-containing dielectric layer leading to a gain in Jsc, open circuit voltage,Voc, Fill-Factor, FF, and efficiency.

Textile dyes as photo-sensitizer in the dye sensitized solar cells

Abstract Exploring the cost-effective alternative materials to replace the synthetic dyes for application in dye sensitized solar cells (DSSC) could help in reducing the overall cost of the devices. Herein, we investigate two cost-effective textile dyes, namely hot reactive dye and vat dye for application in the DSSC. Morphology, domain size, and crystalline phase of the TiO2 nanoparticles in dye loaded TiO2 films are examined in detail by FESEM and X-ray diffraction measurements. Modifications in the absorption spectra of dyes upon adsorption into TiO2 are investigated by UV–Vis analysis. Fourier transform infrared spectroscopy analysis allows us to identify the various functional groups present in the dyes. By comparing the photovoltaic performance, we found that hot reactive dye based DSSC yield power conversion efficiency (PCE) of 1.20%, which is significantly higher than the vat dye based DSSC (0.51%). This is mainly due to superior short-circuit current density (Jsc) and open circuit voltage generated in the hot reactive dye relative to the vat dye based DSSC. The higher Jsc in the hot reactive dye-based device is mainly attributed to the favorable morphology, better crystallinity and superior absorption features of hot reactive dye coated TiO2 film. However, a slightly less fill factor is noticed for hot reactive dye-based devices owing to the lesser shunt resistance in comparison to the vat dye-based device. Although the PCE attained by these devices is far below that of standard DSSC, the present study can be helpful in the development of more eco-friendly and cost-effective solar cells.

Benzoselenadiazole‐core asymmetric D‐A‐A small molecule for solution processed bulk heterojunction organic solar cells

The present work is accounted on the designing of a new and efficient asymmetric organic chromophore, named 4-(3,5-bis [trifluoromethyl] phenyl)-7-(5′-hexyl-[2,2′-bithiophen]-5-yl)-benzo[c [1, 2, 5]selenadiazole, (RT-BSe-F), based on benzoselenadiazole central acceptor building blocks. The acceptor unit of 3,5-bis (trifluoromethyl) benzene and donor unit of alkyl bithiophene attached with benzoselenadiazole central unit showed large impacts on the optical and electrochemical properties. The reasonable optical band gap of ~2.02 eV and HOMO of −5.33 eV were obtained by RT-BSe-F chromophore due to a strong electron accepting nature of fluorine based compound. With 3,5-bis(trifluoromethyl) benzene unit, the absorption of RT-BSe-F chromophore was considerably increased to higher wavelength which might enhance the crystallinity of thin film with high hole mobility. RT-BSe-F chromophore was effectively applied to fabricate the solution-processed bulk-heterojunction organic solar cells (BHJ-OSCs) and attained a high power conversion efficiency (PCE) of ~3.75% accompanying high JSC of ~12.56 mA cm−2, FF of ~0.42 and VOC of ~0.71 V. The obtained high PCE might be associated to a high surface energy of TiO2 layer as buffer and the use of high mobility organic RT-BSe-F chromophore.

Non-edible oil based polyurethane acrylate with tetrabutylammonium iodide gel polymer electrolytes for dye-sensitized solar cells

Polyurethane acrylate (PUA) gel polymer electrolytes were prepared with tetrabutylammonium iodide (TBAI) as the complex salt. Fourier transform infrared spectroscopy results confirmed that the NH, CO, CN and COC polar functional groups formed the coordination with TBA+ cations of salt observed from the bands shift. The maximum ionic conductivity of (1.88 ± 0.02) × 10-4 S cm−1 was obtained for the electrolyte with composition of 67.94 wt% PUA–30.00 wt% TBAI–2.06 wt% I2 (S3 electrolyte) which influenced by the highest charge mobility of (6.24 ± 0.12) × 10-7 cm2 V−1 s−1 and number density of (1.93 ± 0.04) × 1021 cm−3 estimated from fitting the Nyquist plots. The S3 electrolyte was electrochemically stable up to 1.64 V and capable of performing up to 2000 cycles steadily. Triiodide ion diffusivity obtained was 1.70 × 10-8 cm2 s−1. The electrolyte performance in dye-sensitized solar cells (DSSCs) was tested and cell with S3 electrolyte showed the highest solar conversion efficiency of (1.97 ± 0.21)% with short-circuit current density (Jsc) of (7.15 ± 0.74) mA cm−2 and open-circuit voltage (Voc) of (0.55 ± 0.01) V when exposed under 1000 W m−2 light illumination. The highest efficiency obtained was influenced by the high electrons driving force in DSSCs. Low reduction resistance (Rpt) of (2.46 ± 0.08) Ω at the electrolyte/counter electrode interface along with low charge transfer resistance (Rct) of (24.97 ± 0.14) Ω at TiO2/dye/electrolyte interface and charge diffusion resistance (Rd) of (34.14 ± 0.11) Ω in redox electrolyte increase the electrons dynamic, thus resulting high Jsc and hence high DSSC efficiency. This work shows that PUA-based electrolytes have potential for DSSC applications.

Asymmetric ITIC acceptor for asymmetric benzodithiophene polymer solar cells

In this work, one novel asymmetric non-fullerene acceptor ITIC-3T was designed and synthesized. ITIC-3T molecule shows 1.58 eV Eg, with −3.95 eV LUMO level. Utilizing P3 (one asymmetric 2D conjugated benzodithiophene polymer) as donor material, bulk heterojunction solar cells were fabricated. The optimal device yields a PCE of 6.47% with a VOC of 0.64 V, a FF of 55.5% and a high JSC of 18.18 mA cm−2, which may be attributed to the complementary optical absorption of active blend (P3 and ITIC-3T). In general, this work demonstrates that asymmetric polymer donor and non-fullerene acceptor active layer blend is potential for fabricating efficient photovoltaic cells.

The enhancement in cell performance of CdTe-based solar cell with Si/SiO2 distributed Bragg reflectors

In this study, the very effective design that is Distributed Bragg Reflectors (DBRs) technique and Back Surface Field (BSF) layer are used to fabricate the high-efficiency CdTe-based solar cells. The CdTe-based thin-film solar cells are fabricated as SiO2/Si(DBR)/ZnTe (BSF)/CdTe/CdS/ZnO/FTO. Then, the effects of different number of DBRs layers on CdTe-based solar cell are investigated. 68.77% reflection intensity can be obtained even in 1 period and reflection intensity can reach 99.28% in 3 periods. Significant improvement in cell output parameters are observed with increasing DBRs up to 3 periods. The highest JSC, FF and η values are obtained as 109.82 A/m2, 82.03% and 10.39%, respectively. With the rise in the DBR period, the long wavelength tail of the reflection spectrum is drawn into the center of the reflection band and the long wavelength reflectivity is reduced. This narrowing reduces the rate of reflection of low-energy photons that cannot be absorbed by CdTe layer.

A stable gel electrolyte based on poly butyl acrylate (PBA)-co-poly acrylonitrile (PAN) for solid-state dye-sensitized solar cells

This work deals the preparation of a new polymer gel electrolyte using an efficient poly (acrylonitrile)-co-poly (butyl acrylate) (PAN-co-PBA) for solid-state DSSCs. Prepared PAN-co-PBA exhibited the superabsorbent behavior as seen the carboxylate group in copolymer. An excellent gelation with iodide couple and high ionic conductivity of 3.86 mS/cm were recorded for PAN-co-PBA gel electrolyte. Fabricated DSSC with 7% PAN-co-PBA attained the highest overall conversion efficiency of ~5.23% along with high JSC = 13.16 mA/cm2, VOC = 0.646 V and FF = 0.62. Improved DSSC performance might be related to excellent gelation and high ionic conductivity of PAN-co-PBA gel electrolyte, resulting in improving interfacial contact and pore filling.

Improved short-circuit current density in bulk heterojunction solar cells with reduced graphene oxide-germanium dioxide nanocomposite in the photoactive layer

In the quest to improve the optical absorption and electrical transport of poly-3-hexylthiophene (P3HT) and (6-6) phenyl-C61-butyric acid methyl ester (PCBM) blend film, reduced graphene oxide-germanium dioxide nanocomposite (rGO-GeO2) was employed in the photoactive layer of thin film organic solar cells. Bulk heterojunction solar cells (BHJ SCs) with rGO-GeO2 composite in the active layer exhibited an increase in power conversion efficiency (PCE) of up to 53%. Significant improvement in the measured photocurrent is achieved by the incorporation of rGO-GeO2 in the active layer. High short-circuit current density (Jsc) of up to 17 mA/cm2 is attained in the BHJ SCs. The high Jsc shows that the inlay of rGO-GeO2 in the active layer facilitates exciton separation and creates percolation pathways for charge transport to the electrodes. Charge separation is energetically favoured by a built-in potential difference between the donor and acceptor phases of the active layer. Hence, the incorporation of rGO-GeO2 composite in the active layer improves its charge photogeneration, separation and transport to yield high Jsc and enhanced PCE.

Side-chain engineering of A-D-D-A-type small-molecule electron acceptors for high-performance polymer solar cells with Jsc exceeding 22 mA cm−2

One of the effective ways to improve the short-circuit current density (Jsc) of polymer solar cells (PSCs) is to develop near-infrared (NIR) nonfullerene small molecule acceptors (SMAs). Herein, a novel NIR acceptor-donor-donor-acceptor (A-D-D-A)-type SMAs, C6-IDT2-DFIC which is derived from previously reported IDT2-DFIC, was designed and synthesized. By replacing the phenylhexyl group with the hexyl side-chain, the C6-IDT2-DFIC exhibits a wide absorption range in the 550–900 nm, strong intermolecular interactions, higher and more balanced charge mobilities. The device with the PBDB-T:C6-IDT2-DFIC blend film showed a power conversion efficiency (PCE) of 12.33% with a Jsc of 22.57 mA cm−2, which is higher than that of the PBDB-T:IDT2-DFIC device (10.06% with a Jsc of 16.06 mA cm−2). More interestingly, the Jsc of the PBDB-T:C6-IDT2-DFIC device is one of the highest current densities from PBDB-T-based PSCs with optoelectronic response below 900 nm. Our work clearly indicate that side chain engineering is useful to achieve high Jsc of PSCs.

High performance organic solar cells based on ZnO: POT2T as an effective cathode interfacial layer

Interface engineering in organic solar cells (OSCs) plays an important role in improving electron extraction and suppressing carrier recombination. In this article, the improvement of device was achieved by doping POT2T into ZnO as a new electron transport layer (ETL). For PTB7-Th: PC71BM system, the device fabricated by using ZnO as ETL achieved a PCE of 9.03% with a JSC of 17.33 mA/cm2, a VOC of 0.783V and a FF of 64.17%. After doping 5wt% POT2T in ZnO, the JSC increased to 18.01 mA/cm2 and the FF increased slightly to 69.87%, as a result, the PCE increased to 9.84% with about 10% enhancement. The enhancement is attributed to the improved electron transport and conductivity, optimized ZnO surface morphology after adding POT2T, resulting in higher JSC and FF. Therefore, doping POT2T into ZnO as an ETL is a simple and effective method for obtaining high efficient OSCs.

Transparent Thin-Film Silicon Solar Cells for Indoor Light Harvesting with Conversion Efficiencies of 36% without Photodegradation.

With the development of the Internet of Things (IoT), indoor photovoltaics are attracting considerable interest owing to their potential to benefit various IoT-related fields. Therefore, this study investigates the use of transparent hydrogenated amorphous silicon (a-Si:H) solar cells for a broad range of applications, including indoor light harvesting. High-gap triple layers were employed in the a-Si:H solar cells to obtain a high shunt resistance and high short-circuit current, JSC, and open-circuit voltage, VOC, under indoor illumination. Additionally, multiple color-adjusting layers were added without noticeable costs to the conversion efficiency. The maximum efficiency of 36.0% was obtained at a transmittance of 20.44% under white LED light (3000 lx and 0.92 mW cm-2). Furthermore, the fabricated transparent solar cells show excellent long-term performance, sustaining over 99% of original efficiency under continuous indoor light illumination for 200 h. These cells could accelerate the progress of energy harvesting in IoT applications and facilitate the construction of integrated photovoltaics.

Improved Sensitivity of Indirect Organic X-ray Detector Using Ag Nanoparticles Blended in Bulk-Heterojunction Active Layer

Blending effect of Ag nanoparticles (NPs) in bulk-heterojunction P3HT:PC70BM layer was studied to improve the sensitivity of indirect X-ray detector. Scintillator-decoupled detectors with different contents (1, 3, 5 and 7 wt%) of Ag NPs were fabricated and tested using a solar simulator. Compared with the detector having pristine P3HT:PC70BM layer, the detector with 3 wt% Ag NPs blended in the P3HT:PC70BM layer showed 26% higher PCE and 19% higher Jsc. CsI(Tl) scintillator-coupled detectors were then tested under irradiation of X-ray source. The detector with 3 wt% Ag NPs-blended P3HT:PC70BM layer showed the highest CCD of 350.51 nA/cm2 and the highest sensitivity of 2.20 mA/Gy · cm2. At optimal Ag NPs blending condition, Ag NPs in the P3HT:PC70BM layer can enhance charge-generation by improving absorption of visible-photons and charge-extraction by improving carrier-mobility while lowering resistance.

A thiophene-fused benzotriazole unit as a “π-bridge” in A-π-D-π-A type acceptor to achieve more balanced JSC and VOC for OSCs

As known, to balance the open-circuit voltage (VOC) and short-circuit current density (JSC) is one of the effective strategies to improve the photovoltaic performances of OSCs. In this work, a thiophene-fused benzotriazole (BTAZT) unit acts as a “π-bridge” to build an acceptor (A3) with A-π-D-π-A structure for OSCs. Compared with a thiophene-fused benzothiadiazole (BTT) unit as a “π-bridge” in our previous acceptor (A2), BTAZT unit exhibits relatively weak electron-withdrawing ability that results in a significant uplift of LUMO energy level to favor for enhancement of VOC. Also, the fusion of a thiophene ring onto BTAZ unit strengthens the intramolecular charge transfer to maintain the relatively high JSC. Therefore, the PTB7-Th:A3 OSC device shows higher PCE of 11.0% with more balanced device parameters (VOC = 0.959 V, JSC = 17.30 mA cm−2, FF = 66.2%) as well as smaller energy loss (Eloss) of 0.63 eV than the PTB7-Th:A2 device with PCE of 8.20% (VOC = 0.701 V, JSC = 19.47 mA cm−2, FF = 60.1% and Eloss = 0.67 eV). This work indicates that the rational structural modification of a “π-bridge” for A-π-D-π-A type acceptor is an effective approach to achieve the balanced VOC and JSC for the OSCs.

Effects of oxidation state on photovoltaic properties of reactively magnetron sputtered hole-selective WOx contacts in silicon heterojunction solar cells

The stoichiometry value x of WOx, or its oxidation state, is crucial for improving performances of the hole-selective contact heterojunction silicon solar cell. However, it is challenging to tune the films’ oxidation state using the well-known evaporation method. In this study, a simulation was performed to analyze the effect of x on short-circuit current (Jsc) loss, attributed to the hole-selective contact in the device. Compared to the thickness of WOx layer, x has a more important role in minimizing Jsc loss. Based on the simulation, the WOx/c-Si heterojunction solar cells having hole-selective WOx contacts with tuned x to vary its oxidation state were fabricated using reactive magnetron sputtering. The relationships of the open-circuit voltage (Voc) and Jsc with respect to x were similar. The experimentally determined Jsc increased from 34.7 to 36.6 mA cm−2 when x was increased from 2.72 to 2.77; this result is consistent with the simulation. Nevertheless, fill factor (FF) reduced with the increase of x, owing to the reduced conductivity of WOx. Both oxidation state and film conductivity must be as high as possible to simultaneously achieve high Voc, Jsc, and FF. The lowest x yielded a solar cell efficiency of 13.3%.

Maximizing Short Circuit Current Density and Open Circuit Voltage in Oxygen Vacancy-Controlled Bi1-xCaxFe1-yTiyO3-δ Thin-Film Solar Cells.

Designing solid-state perovskite oxide solar cells with large short circuit current (JSC) and open circuit voltage (VOC) has been a challenging problem. Epitaxial BiFeO3 (BFO) films are known to exhibit large VOC (>50 V). However, they exhibit low JSC (≪μA/cm2) under 1 Sun illumination. In this work, taking polycrystalline BiFeO3 thin films, we demonstrate that oxygen vacancies (VO) present within the lattice and at grain boundary (GB) can explicitly be controlled to achieve high JSC and VOC simultaneously. While aliovalent substitution (Ca2+ at Bi3+ site) is used to control the lattice VO, Ca and Ti cosubstitution is used to bring out only GB-VO. Fluorine-doped tin oxide (FTO)/Bi1-xCaxFe1-yTiyO3-δ/Au devices are tested for photovoltaic characteristics. Introducing VO increases the photocurrent by four orders (JSC ∼ 3 mA/cm2). On the contrary, VOC is found to be <0.5 V, as against 0.5-3 V observed for the pristine BiFeO3. Ca and Ti cosubstitution facilitate the formation of smaller crystallites, which in turn increase the GB area and thereby the GB-VO. This creates defect bands occupying the bulk band gap, as inferred from the diffused reflection spectra and band structure calculations, leading to a three-order increase in JSC. The cosubstitution, following a charge compensation mechanism, decreases the lattice VO concentration significantly to retain the ferroelectric nature with enhanced polarization. It helps to achieve VOC (3-8 V) much larger than that of BiFeO3 (0.5-3 V). It is noteworthy that as Ca substitution maintains moderate crystallite size, the lattice VO concentration dominates GB-VO concentration. Notwithstanding, both lattice and GB-VO contribute to the increase in JSC; the former weakens ferroelectricity, and as a consequence, undesirably, VOC is lowered well below 0.5 V. Using optimum JSC and VOC, we demonstrate that the efficiency ∼0.22% can be achieved in solid-state BFO solar cells under AM 1.5 one Sun illumination.

Novel Nitrogen-Containing Heterocyclic Non-Fullerene Acceptors for Organic PhotovoltaicCells: Different End-Capping Groups Leading to a Big Difference of Power Conversion Efficiencies.

Novel cores for high performance nonfullerene acceptors (NFAs) remain to be developed. In this work, two new n-type nitrogen-containing organic heterocyclic NFAs, namely, BDTN-BF and BDTN-Th, were designed and synthesized based on a new seven fused-ring core (BDTN) with two different end-capping groups. As a result, BDTN-BF possessed similar absorption spectra in solution and solid state to BDTN-Th, but a slightly higher maximum molar extinction coefficient. Manufacturing the polymer solar cells with PM6 as the donor, the photovoltaic performance of BDTN-BF and BDTN-Th was investigated. The PM6:BDTN-BF-based device achieved the highest power conversion efficiency (PCE) of 11.54% with a high Jsc of 20.20 mA cm-2, a fill factor (FF) of 61.46%, and a large Voc of 0.93 V, and the energy loss (Eloss) was calculated to be 0.48 eV. Comparatively, the PM6:BDTN-Th-based device achieved the maximum PCE value of only 3.53% because of inadequate Jsc and FF. The higher Jsc and FF for the PM6:BDTN-BF-based device was mainly due to the effective electron transfer from PM6 to BDTN-BF, more balanced μh/μe, higher electron mobility of the neat film, better charge collection and dissociation efficiency, and more favorable morphology. These results demonstrate that the acceptors with nearly identical absorption spectra could result in a significant difference in photovoltaic performance, which stress the importance of end-capping units. Furthermore, few NFA-based devices achieve large Voc and high Jsc simultaneously as one based on PM6:BDTN-BF, indicating that nitrogen hybridization of NFAs may be an efficient strategy to realize high and balanced Voc and Jsc.

Simultaneously improving the photovoltaic parameters of organic solar cells via isomerization of benzo[b]benzo[4,5]thieno[2,3-d]thiophene-based octacyclic non-fullerene acceptors

Three isomeric FREAs were synthesized and applied in organic solar cells. The OSC devices based on Z1-bb exhibited a PCE of 12.66%. The isomerization of a fused-ring core could be achieve high-performance OSCs with high Jsc, Voc, and FF.

Over 14% efficiency all-polymer solar cells enabled by a low bandgap polymer acceptor with low energy loss and efficient charge separation

A low bandgap polymer acceptor PF5-Y5 was synthesized and its all-PSCs achieved an impressive device efficiency of 14.45% with both high Voc and Jsc due to the excellent absorption coverage, small energy loss, and efficient charge separation.