Output Power Conversion Efficiency Research Articles

Fabrication and comprehensive investigations on NBD-based luminescent solar concentrator

The design and development of innovative chromophoric materials for luminescent solar concentrators (LSCs) is an emerging area of research in the pursuit of low-cost photovoltaic technology. In this study, we devised and developed the optically active fluorescent dye NBDNH2 based on the skeleton of a benzoxadiazole. In NBDNH2, the electron donating amino group and the electron-withdrawing nitro group are the responsible for intramolecular charge transfer transition as well as fluorescence upon photoexcitation. The structural and photophysical properties of NBDNH2 dye have been meticulously investigated. In addition, the solvent-property relationships also investigated through time-resolved fluorescence and 1H NMR measurements. The photophysical studies reveal that the dye has a moderate Stokes shift, a long fluorescence lifetime and provides guidance for the development of LSCs. NBDNH2 was doped in polymethyl methacrylate (PMMA) to fabricate LSC devices. Due to promising optical properties, the NBDNH2 based LSC (5 × 5 × 0.3 cm3) showed the internal and external photon efficiencies as high as 29.4 % and 3.84 %, respectively. When connected with the photovoltaic cell, the champion device yielded power conversion efficiency of 1.32 % and 0.64 % with scattering and black background, respectively. Based on the findings, we unequivocally envisaged that the benzoxadiazole-based ICT probe is a prospective optical material for LSC applications.

Laminated 2D-Ti3C2-MXenes as high-performance counter electrode for triiodide reduction in dye-sensitized solar cells

The different surface terminals, sizes, and sheet quality of laminated 2D-Ti3C2-MXenes were prepared by selective etching intermediate Al atoms layer form the strongly bonded compound Ti3AlC2 as precursor at low temperature using different etchants of HF, HF + HCl, LiF + HCl, and NH4HF2 for 24 h, respectively. Then, 2D-Ti3C2-MXenes were further instead of traditional Pt as counter electrodes (CEs) in triiodide reduction for dye-sensitized solar cells (DSSCs). The selection of different etchant directly affects the properties and performance of the laminated 2D-Ti3C2-MXenes catalyst. Herein, the DSSCs with 2D-Ti3C2-MXenes CEs yielded power conversion efficiencies (PCE) of 7.15 % (HF-), 6.06 % (HF + HCl-), 6.38 % (LiF + HCl-), and 6.05 % (NH4HF2-) for regenerate traditional I3−/I− shuttles via the photocurrent-voltage (J-V) test, respectively. The outstanding electrocatalytic performances of laminated 2D-Ti3C2-MXenes can be attributed to the formation of regular inter-stratification structures by etching to expose larger specific surface areas and further generate more catalytic reaction sites, as well as the acceleration of I3−/I− shuttle diffusion channels by adjusting the interlayer d-spacing, implying a potentially candidate of Pt catalyst for applications in the encapsulated DSSCs as Pt-free CEs.

Aspartate all-in-one doping strategy enables efficient all-perovskite tandems.

All-perovskite tandem solar cells hold great promise in surpassing the Shockley-Queisser limit for single-junction solar cells1-3. However, the practical use of these cells is currently hampered by the subpar performance and stability issues associated with mixed tin-lead (Sn-Pb) narrow-bandgap perovskite subcells in all-perovskite tandems4-7. In this study, we focus on the narrow-bandgap subcells and develop an all-in-one doping strategy for them. We introduce aspartate hydrochloride (AspCl) into both the bottom poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) and bulk perovskite layers, followed by another AspCl posttreatment. We show that a single AspCl additive can effectively passivate defects, reduce Sn4+ impurities and shift the Fermi energy level. Additionally, the strong molecular bonding of AspCl-Sn/Pb iodide and AspCl-AspCl can strengthen the structure and thereby improve the stability of Sn-Pb perovskites. Ultimately, the implementation of AspCl doping in Sn-Pb perovskite solar cells yielded power conversion efficiencies of 22.46% for single-junction cells and 27.84% (27.62% stabilized and 27.34% certified) for tandems with 95% retention after being stored in an N2-filled glovebox for 2,000 h. These results suggest that all-in-one AspCl doping is a favourable strategy for enhancing the efficiency and stability of single-junction Sn-Pb perovskite solar cells and their tandems.

Structural optimization of inverted CsPbI2Br perovskite solar cells for enhanced performance via SCAPS-1D simulation

The CsPbI2Br material benefits perovskite solar cells (PSCs) by balancing their efficiency with chemical and thermal stability. Herein, we performed numerical modeling of a p-i-n structured PSCs employing different electron transport layers (ETLs). In order to optimize the ETL, the simulation results showed bilayer ETL (PCBM/SnO2) yielded the best device performance. Then, by tweaking the absorber layer’s defect density, thickness, electron affinity, and band gap, we optimized the device performance utilizing this bilayer ETL and yielded power conversion efficiency (PCE) of 12.51%, fill factor (FF) of 73.60%, open circuit voltage (V OC ) of 0.94 V, and short circuit current density (J SC ) of 17.94 mA cm−2. These CsPbI2Br perovskite-based devices would have outstanding thermal stability in a range from 253 K to 323 K. Another important observation in these PSCs is that interfacial defect density plays a crucial for regulating the V OC. We, therefore, anticipate that this research will aid in the development of extremely effective and stable inverted all inorganic PSCs.

Metal‐free Organic Dyes Featuring an Azobenzene Bridge for Photochromic Dye‐Sensitized Solar Cells

AbstractWe report the facile synthesis of photochromic donor‐π‐acceptor (D‐π‐A) dyes featuring an azobenzene spacer with diphenylamine and dimethylamine as donor residues (DPAC and DMAC). We also investigate the spectroscopic and electrochemical properties of these dyes and their application to dye‐sensitized solar cells (DSSCs). The trans‐cis isomerization of the azobenzene bridge permits regulation of the photovoltaic behaviour in the DSSCs containing iodine‐ and cobalt‐based redox electrolytes. The iodidie/triiodidie redox shuttle is suitable for DMAC‐DSSCs, whereas the cobalt redox mediator is optimal for DPAC‐DSSCs. DMAC‐ and DPAC‐DSSCs yield power conversion efficiencies (PCEs) up to 1.99 % and 1.08 % under one sun illumination, when the solar cells are at the photostationary (PS) state.

Polyoxovanadate derived VN@C composite catalysts by different synthesis routes as Pt-free counter electrode for dye-sensitized solar cells

Vanadium-based nitrides have been applied as Pt-free counter electrodes (CEs) electro-catalysts for dye-sensitized solar cells (DSSCs) due to inexpensive cost and easy doping and modification. Herein, polyoxovanadate (NH4)2V6O16 assisted by melamine to prepare VN@C composites by five different synthesis routes, including solvothermal, sol–gel, hydrothermal, ball milling, and chemical mixing method. And then, five VN@C composites were assembled as CEs in the encapsulated DSSCs, and yielded power conversion efficiencies of 4.47, 5.04, 5.35, 5.49 and 6.11% for regenerate traditional I3−/I− shuttles by the photocurrent-photovoltage (J-V) test, respectively. The catalytic performances of VN@C composites CEs were assessed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Tafel polarization experiments, and the significant effects of different synthetic routes were confirmed. The results revealed that VN@C composite CEs prepared by chemical mixing method had higher catalytic performance in DSSCs, which is due to the improvement of conductivity and the high concentration of active sites.

Iodine‐Stabilized Organic Nanoparticle Dispersions for the Fabrication of 10% Efficient Non‐Fullerene Solar Cells

AbstractHigh‐performance organic solar cells are deposited from eco‐friendly semiconductor dispersions by applying reversible electrostatic stabilization while omitting the need for stabilizing surfactants. The addition of iodine fosters the oxidation (p‐doping) of the light‐harvesting polymer, effectively promoting the electrostatic repulsion of the nanoparticles and hence the colloidal stability of the respective dispersions. The oxidation of polymers with iodine is reversible: after thin‐film deposition and after thermal evaporation of the iodine, the corresponding polymer:non‐fullerene solar cells yield power conversion efficiencies of up to 10.6%.

Molten Salt Strategy for Reproducible Evaporation of Efficient Perovskite Solar Cells

AbstractVacuum evaporation is promising for the scalable fabrication of perovskite solar cells (PSCs). Nevertheless, the poor thermal conductivity of metal halide powder leads to unfavorable temperature inhomogeneity, which destabilizes the evaporation rate, posing a major challenge to the reproducible deposition of perovskite films, particularly by coevaporation. Herein, a molten salt strategy is reported for sequentially vacuum evaporation of PSCs. The molten salt increases the thermal conductivity of metal halides and greatly homogenizes the temperature, which stabilizes the evaporation rate and the composition of the resulting perovskite films. The PSCs yield power conversion efficiencies (PCEs) of ≈24% with exceptional reproducibility. The unencapsulated PSCs maintain 85% of the initial PCE after 3600 h of maximum power point tracking and maintain 85% of the initial PCE after being heated at 60 °C for 3000 h. The molten salt strategy opens a new avenue for the application of evaporation in perovskite optoelectronics.

Modeling and numerical simulation of high efficiency perovskite solar cell with three active layers

Recently, organic–inorganic metal halide perovskites, due to their promising optical properties, are widely used in solar cell applications yielding power conversion efficiencies (PCE) above 21%. In this study, using solar cell capacitance one-dimensional tool (SCAPS-1D), we have numerically simulated a novel solar cell consisting of three perovskite absorbers (MASnI3, MAPbI3 and FAMASnGeI3) as the active layer and achieved power conversion efficiency of 30.77%. We have also compared the performance of the proposed triple active layer perovskite solar cell (PSC) with single (MAPbI3) and double (MASnI3, MAPbI3) active layer PSCs and observed that the triple active layer PSC outperforms the single and double layer structures. Moreover, changing hole transport layer (HTL), it is found that inorganic Cu2O can be a suitable substitute for expensive prevalent organic Spiro-OMeTAD as HTL of our PSC and enhances the device PCE to 31.04%. In addition, by increasing the first absorber layer’s (MASnI3) thickness, while maintaining the total active layer thickness constant, a high PCE of 31.44% for triple active layer PSC is achieved. Furthermore, it is shown that materials with work functions more than 4.4 eV are not appropriate to be used as front contact of this structure. Finally, our simulations indicate that increase of defect density in absorber layers and working temperature of the cell monotonically degrade the efficiency of the device. We believe that the proposed triple active layer PSC can open a new route for realization of highly efficient PSCs.

A Self-Formed Stable PbI2 /NiOx Interface with Increased Ni3+ Centers for Perovskite Photovoltaics.

Nickel oxide (NiOx ) is a promising hole transport material (HTM) for perovskite photovoltaics owing to its chemical stability and low cost. However, most NiOx based solar cells deliver relatively weak performance because of its insufficient electrical property and interfacial contact. In this work, a self-formed PbI2 /NiOx interface was developed to stabilize the Ni3+ centers, which was beneficial for electrical transport and band alignment in perovskite solar cells. Combined with ultraviolet ozone treatment (UVO) and sequential deposition, the density of Ni3+ centers was greatly increased and could be stabilized by the PbI2 interface. These merits contributed coordinately to the fast hole extraction and low energy loss across the PbI2 /NiOx interface, yielding power conversion efficiencies (PCEs) of over 19 %.

Dopant-free Hole-transporting Materials for CH3NH3PbI3 Inverted Perovskite Solar Cells with an Approximate Efficiency of 20%

A D-π–A-π–A-π-D structure-based small organic molecule (YJ01) has been demonstrated as an efficient dopant-free hole-transporting material (HTM) for inverted perovskite solar cells (iPSCs). The conjugation and twisted angles are balanced by the 1,4-di((E)-styryl)benzene core that bears two electron-withdrawing cyan groups. The cyan positions on the central core have a significant impact on the HTM properties. The outstanding performance of the iPSC device employing indium-doped tin oxide/pristine HTM/CH3NH3PbI3/PCBM/BCP/Ag based on YJ01 yielded an efficiency of 19.85% with a Voc of 1.08 V, Jsc of 22.53 mA cm–2, and FF of 0.815. The device which was based on YJ02 yielded power conversion efficiency (PCE) of 17.5%. The devices retained 80% of their original PCE after 500 h in an ambient environment. The hole motilities of YJ01 and YJ02 were determined to be 5.68 × 10–3 cm2 V–1 s–1 and 1.55 × 10–3 cm2 V–1 s–1, respectively. The large efficiency difference between YJ01 and YJ02 is attributed to the enlargement of the substitution distance between the two cyan units given the much greater reduction of solid-state fluorescence emission for YJ01 compared with YJ02. Thus, it is hoped to provide a good strategy for the HTM design, facilitating highly efficient and stable iPSCs.

Regio‐Regular Polymer Acceptors Enabled by Determined Fluorination on End Groups for All‐Polymer Solar Cells with 15.2 % Efficiency

AbstractPolymerization sites of small molecule acceptors (SMAs) play vital roles in determining device performance of all‐polymer solar cells (all‐PSCs). Different from our recent work about fluoro‐ and bromo‐ co‐modified end group of IC‐FBr (a mixture of IC‐FBr1 and IC‐FBr2), in this paper, we synthesized and purified two regiospecific fluoro‐ and bromo‐ substituted end groups (IC‐FBr‐o & IC‐FBr‐m), which were then employed to construct two regio‐regular polymer acceptors named PYF‐T‐o and PYF‐T‐m, respectively. In comparison with its isomeric counterparts named PYF‐T‐m with different conjugated coupling sites, PYF‐T‐o exhibits stronger and bathochromic absorption to achieve better photon harvesting. Meanwhile, PYF‐T‐o adopts more ordered inter‐chain packing and suitable phase separation after blending with the donor polymer PM6, which resulted in suppressed charge recombination and efficient charge transport. Strikingly, we observed a dramatic performance difference between the two isomeric polymer acceptors PYF‐T‐o and PYF‐T‐m. While devices based on PM6:PYF‐T‐o can yield power conversion efficiency (PCE) of 15.2 %, devices based on PM6:PYF‐T‐m only show poor efficiencies of 1.4 %. This work demonstrates the success of configuration‐unique fluorinated end groups in designing high‐performance regular polymer acceptors, which provides guidelines towards developing all‐PSCs with better efficiencies.

Regio-Regular Polymer Acceptors Enabled by Determined Fluorination on End Groups for All-Polymer Solar Cells with 15.2 % Efficiency.

Polymerization sites of small molecule acceptors (SMAs) play vital roles in determining device performance of all-polymer solar cells (all-PSCs). Different from our recent work about fluoro- and bromo- co-modified end group of IC-FBr (a mixture of IC-FBr1 and IC-FBr2), in this paper, we synthesized and purified two regiospecific fluoro- and bromo- substituted end groups (IC-FBr-o & IC-FBr-m), which were then employed to construct two regio-regular polymer acceptors named PYF-T-o and PYF-T-m, respectively. In comparison with its isomeric counterparts named PYF-T-m with different conjugated coupling sites, PYF-T-o exhibits stronger and bathochromic absorption to achieve better photon harvesting. Meanwhile, PYF-T-o adopts more ordered inter-chain packing and suitable phase separation after blending with the donor polymer PM6, which resulted in suppressed charge recombination and efficient charge transport. Strikingly, we observed a dramatic performance difference between the two isomeric polymer acceptors PYF-T-o and PYF-T-m. While devices based on PM6:PYF-T-o can yield power conversion efficiency (PCE) of 15.2 %, devices based on PM6:PYF-T-m only show poor efficiencies of 1.4 %. This work demonstrates the success of configuration-unique fluorinated end groups in designing high-performance regular polymer acceptors, which provides guidelines towards developing all-PSCs with better efficiencies.

Comparative performances of nature-based dyes extracted from Baobab and Shea leaves photo-sensitizers for dye-sensitized solar cells (DSSCs)

Dye-sensitized solar cells (DSSCs) were fabricated using dye extracts from Baobab and Shea leaves as photo-sensitizers. The photoanode was made from spin-coating of titanium dioxide (TiO2) and annealed at 450°C for 1 ​h. The TiO2 shows good optical absorption capability in the ultraviolet region with a band gap of 3.3 ​eV and surface morphology that revealed grains that are spherical and randomly oriented with average particle size of (26±4.0) nm. The Shea and Baobab dyes have shown absorption at the blue-yellow region of the visible light with energy band gap of 1.66 ​eV and 1.89 ​eV respectively. The Shea-based DSSC (SDSSC) yielded power conversion efficiency (PCE) of (0.25±0.13) % with short current density, Jsc, open-circuit voltage, Voc and fill factor, FF of (2.66±1.61)mAcm−2, (0.158±0.0877) V and 0.596 ​± ​0.389, respectively while Baobab-based DSSCs (BDSSCs) gave lower PCE of (0.11±0.028) % with Jsc, Voc and FF of (0.286±0.0483)mAcm−2,0.676±0.0622 V and 0.592±0.0339. Light soaking tests show that SDSSCs are more stable in photoelectric performance than BDSSCs for 5 ​h. Hence, preferred as a sensitizer for better performance in dye-sensitized solar cells than Baobab dye extract.

Revealing the electronic structure, heterojunction band offset and alignment of Cu2ZnGeSe4: a combined experimental and computational study towards photovoltaic applications.

Cu2ZnGeSe4 (CZGSe) is a promising earth-abundant and non-toxic semiconductor material for large-scale thin-film solar cell applications. Herein, we have employed a joint computational and experimental approach to characterize and assess the structural, optoelectronic, and heterojunction band offset and alignment properties of a CZGSe solar absorber. The CZGSe films were successfully prepared using DC-sputtering and e-beam evaporation systems and confirmed by XRD and Raman spectroscopy analyses. The CZGSe films exhibit a bandgap of 1.35 eV, as estimated from electrochemical cyclic voltammetry (CV) measurements and validated by first-principles density functional theory (DFT) calculations, which predicts a bandgap of 1.38 eV. A fabricated device based on the CZGSe as a light absorber and CdS as a buffer layer yields power conversion efficiency (PCE) of 4.4% with VOC of 0.69 V, FF of 37.15, and Jsc of 17.12 mA cm-2. Therefore, we suggest that interface and band offset engineering represent promising approaches to improve the performance of CZGSe devices by predicting a type-II staggered band alignment with a small conduction band offset of 0.18 eV at the CZGSe/CdS interface.

Improving thin film solar cells performance via designing moth-eye-like nanostructure arrays

Herein, bioinspired moth-eye-like nanostructures are presented as a possible solution for overcoming the limitation of weak absorption by thin film silicon solar cells. The interaction mechanism between the incident wave and such an artificial nanostructure is revealed by using the finite-difference time-domain method. Optical simulations show that the addition of biomimetic nanostructured surface reduces the refractive indices difference from external media environment to cell devices, thereby leads more incident light propagated into the active material. The optical design yield power conversion efficiencies of 14.6% and 17.5% for 2 and 5 μm thick absorbing layers, respectively. Further analysis depended on the equivalent medium theory demonstrates that a smooth, non– abrupt effective refractive index curve plays a key role for the light harvesting. The proposed method of addressing the weak absorption problem by thin film solar cells shows great promise.

(Invited) Interfacial Engineering for High Voltage Performance of Perovskite Photovoltaic Cells

Since our first discovery of perovskite solar cell (PSC) in 2009, enormous efforts have been put into different aspects of PSCs and the progress has been incredibly fast on all fronts. The background, on-going R&Ds, and future direction of PSC research have been reported by our group as a comprehensive review.1 Although efficiency level has reached 25%, PSCs face serious challenges of practical stability and durability required for industrialization. Compositional engineering of lead halide perovskites by mixing different cations and anions, using modulator molecules and mixing 2D and 3D structures have improved the stability of perovskites against heat and moisture. However, organic cations in halide perovskites (methylammonium, etc.) and use of diffusible ionic dopants in hole transport materials (HTMs) are responsible for low stability of perovskites at high temperatures (>120oC). In this respect, use of all-inorganic perovskite materials and dopant-free HTMs is highly desired.2 We have conducted the device fabrication in this direction using CsPbI3 and CsPbI2Br as solution-processed perovskite films. The perovskite absorbers were made into junction with dopant-free HTMs to develop thermally stable PSCs.By chemical engineering to improve the quality of interfacial structure at the hetero-junction, all-inorganic and dopant-free PSCs yielded power conversion efficiency up to 15%. Further we could enhance the open-circuit voltage (Voc) of this PSC up to 1.42V, which is the highest Voc ever achieved with a single perovskite cell.3 In preparation of all-inorganic perovskites, a big challenge should also be directed to development of lead-free perovskite materials for environmental safety in practical applications.2 Among extensive applications of PSCs for outdoor and indoor power generation, use of PSCs in space environments is promising because thin perovskite photovoltaic films demonstrate high stability and tolerance against exposure to high energy particle irradiations (proton and electron beams).4 Thin absorbers (<500 nm) avoid accumulation of particles and due to intrinsic defect tolerant nature of perovskites, radiation-induced collision damage is highly suppressed. Our current efforts in making PSCs based on both lead and lead-free perovskites, and future perspectives of perovskite photovoltaics will be presented.

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.

Efficient inverted perovskite solar cells with CuSeCN as the hole transport material

We demonstrate herein a mixed solvent containing organic amines and water for the solution processing of CuSeCN and apply it as the hole-transport material for stable and efficient inverted perovskite solar cells for the first time. The obtained CuSeCN film is characterized with X-ray diffraction spectrum, X-ray photoelectron spectroscopy, scanning electron microscope, and current-potential characteristics. High-quality perovskite film can be formed on the CuSeCN film obtained from the spin-coating of CuSeCN solution in a mixture solvent of H2O, ethanolamine (ETA), ethylenediamine (EDA), diethanolamine (DTA) with volume ratio of 2:6:1:1. The CuSeCN-based perovskite solar cell yields power conversion efficiency of 15.61% at forward scan and 15.97% at reverse scan with negligible hysteresis and good stability. As compared to the typically used thioether-based solvents for the solution processing of CuSCN, the mixture solvent proposed in this work is less volatile and much cheaper, which is critical for practical applications of perovskite solar cells.

Hydrothermal Synthesis of Aqueous-Soluble Copper Indium Sulfide Nanocrystals and Their Use in Quantum Dot Sensitized Solar Cells.

A facile hydrothermal method to synthesize water-soluble copper indium sulfide (CIS) nanocrystals (NCs) at 150 °C is presented. The obtained samples exhibited three distinct photoluminescence peaks in the red, green and blue spectral regions, corresponding to three size fractions, which could be separated by means of size-selective precipitation. While the red and green emitting fractions consist of 4.5 and 2.5 nm CIS NCs, the blue fraction was identified as in situ formed carbon nanodots showing excitation wavelength dependent emission. When used as light absorbers in quantum dot sensitized solar cells, the individual green and red fractions yielded power conversion efficiencies of 2.9% and 2.6%, respectively. With the unfractionated samples, the efficiency values approaching 5% were obtained. This improvement was mainly due to a significantly enhanced photocurrent arising from complementary panchromatic absorption.