Separator-free Zn-ion Battery with Mn:V3O7·H2O Nanobelts and a Zn2+-Polyacrylamide Semisolid Electrolyte with Ultralong Cycle Life.

Vanadium based oxides are immensely suitable for zinc-ion-batteries (ZIBs) due to their layered and stable crystal structures. In this study, Mn doped V3O7·H2O nanobelts were synthesized and used as cathodes in ZIBs for the very first time and the doped oxide exhibited an enhanced capacity of 258 mAh g-1 compared to its undoped counterpart (208 mAh g-1) at the same current density of 40 mA g-1. Mn:V3O7·H2O outperforms the V3O7·H2O due to the superior bulk electrical conductivity as well as higher nanoscale current carrying capability imparted by a high proportion of mixed valent states of Mn3+, Mn2+, V5+, and V4+ and the smaller crystallite size that affords short diffusion lengths for Zn2+ ions. The Mn:V3O7·H2O cathode is coupled with a Zn2+ ion conducting polyacrylamide gel electrolyte and a Zn flakes/activated carbon (Zn Fs/C) composite anode to yield a unique separator free Mn:V3O7·H2O/Zn2+-PAM gel/Zn-Fs/C battery. The cell exhibits a capacity of ∼205 mAh g-1 (at 40 mA g-1) and retains 99% of its original capacity after 3500 cycles. The Zn2+-PAM gel shows a high ionic conductivity in the range of 5.9 to 28.2 S cm-1, over a wide temperature span of 0 to 70 °C, and a wide electrochemical potential stability window of -0.5 to +2.3 V, thus rendering it suitable for low temperature applications as well. The gel also inhibits dendritic growth of Zn over the Zn-Fs/C anode through regulated flow of Zn2+ ions during charging, prevents cathode dissolution, and improves cycle life via preservation of structural integrity of the Mn:V3O7·H2O cathode after 200 charge-discharge cycles. This is a highly scalable cell configuration and opens up opportunities to produce long lasting batteries completely free of costly separators with a semisolid free-standing electrolyte and a robust doped oxide.

Progress of Photocapacitors.

In response to the current trend of miniaturization of electronic devices and sensors, the complementary coupling of high-efficiency energy conversion and low-loss energy storage technologies has given rise to the development of photocapacitors (PCs), which combine energy conversion and storage in a single device. Photovoltaic systems integrated with supercapacitors offer unique light conversion and storage capabilities, resulting in improved overall efficiency over the past decade. Consequently, researchers have explored a wide range of device combinations, materials, and characterization techniques. This review provides a comprehensive overview of photocapacitors, including their configurations, operating mechanisms, manufacturing techniques, and materials, with a focus on emerging applications in small wireless devices, Internet of Things (IoT), and Internet of Everything (IoE). Furthermore, we highlight the importance of cutting-edge materials such as metal-organic frameworks (MOFs) and organic materials for supercapacitors, as well as novel materials in photovoltaics, in advancing PCs for a carbon-free, sustainable society. We also evaluate the potential development, prospects, and application scenarios of this emerging area of research.

Effect of Cuprous Oxide Nanocubes and Antimony Nanorods on the Performance of Silicon Nanowire-Based Quasi-Solid-State Solar Cell.

Antimony nanorods (SbNRs) anchored to vertically aligned SiNWs serve as cosensitizers and enhance the light absorption of NWs, and their favorably positioned valence band (VB) coupled with their p-type semiconducting nature allows fast hole extraction from SiNWs. Photocorrosion of SiNWs is effectively prevented by a monolayer of N-[3-(trimethoxysilyl)propyl]aniline (TMSPA). Upon assembling a quasi-solid-state solar cell with a SbNRs@TMSPA@SiNW photoanode, a triiodide-iodide (I3 -/I-) redox couple-based gel encompassing dispersed p-type cuprous oxide nanocubes (Cu2O NCs) as the hole transport material. and an electrocatalytic NiO as the counter electrode, a power conversion efficiency (PCE) of 4.7% (under 1 sun) is achieved, which is greater by 177% relative to an analogous cell devoid of the Cu2O NCs and SbNRs. SbNRs at the photoanode maximize charge separation and suppress electron-hole and electron-I3 - recombination at the photoanode/electrolyte interface, thereby improving the overall current collection efficiency. Concurrently, the Cu2O NCs facilitate hole scavenging from SbNRs or SiNWs and relay them rapidly to the I- ions in the electrolyte. Optically transparent and mesoporous NiO with a VB conducive to accepting electrons from FTO permits abundant interaction with I3 - ions. The high PCE is a cumulative outcome of the synergistic attributes of SbNRs, Cu2O NCs, and NiO. The SbNRs@TMSPA@SiNWs/Cu2O-gel/NiO solar cell also exhibits a noteworthy operational stability, for it endures 500 h of continuous 1 sun illumination accompanied by an ∼24.4% drop in its PCE. The solar cell architecture in view of the judiciously chosen components with favorable energy level offsets, semiconducting/photoactive properties, and remarkable stability opens up pathways to adapt these materials to other solar cells as well.

NiMoO4@NiMnCo2O4 Heterostructure: A Poly(3,4-propylenedioxythiophene) Composite-Based Supercapacitor Powers an Electrochromic Device.

The hierarchical heterostructure of NiMoO4@NiMnCo2O4 (NMO@NMCO) with furry structures of NMCO juxtaposed with NMO nanowires are endowed with multiple electrochemically active and accessible sites for ion storage, thus delivering an ultrahigh specific capacitance of 2706 F g-1, nearly two-fold times greater than that of sole NMCO. Electrodeposition of an overlayer of a highly robust and electrically conducting polymer, poly(3,4-propylenedioxythiophene) (PProDOT), not only improves the energy storage performance but also assists the binary oxide cathode in retaining its structural integrity during redox cycling. Coupling with an anode of porous flaky carbon (FC) derived from groundnut shells results in an asymmetric supercapacitor of FC//PProDOT@NiMoO4@NiMnCo2O4, which delivers an outstanding capacitance of 552 F g-1, energy and power density ranges of 172-40 Wh kg-1 and 0.75-10 kW kg-1, respectively, and a remarkable cycle life of 50 000 cycles, with ∼97.8% capacitance retention, over an operational voltage window of 1.5 V. From an application perspective, the charged supercapacitor was connected to a complementary coloring reversible electrochromic device (ECD) of Prussian blue//PProDOT, and the ECD state transformed from a pale-blue to a deep blue hue, thus signaling the efficient utilization of energy stored in the supercapacitor. The energy-saving attribute of the ECD was realized in terms of an integrated visible-light modulation of 39% that accompanied the optical transition. Deployment of low-cost devices at homes and commercial spaces, capable of storing and saving energy, is the way forward, and this is one significant step in this direction.

NiCo Metal-Organic Framework and Porous Carbon Interlayer-Based Supercapacitors Integrated with a Solar Cell for a Stand-Alone Power Supply System.

Nickel cobalt-metal-organic framework (NiCo-MOF), with a semihollow spherical morphology composed of rhombic dodecahedron nanostructures, was synthesized using a scalable and facile wet chemical route. Such a structure endowed the material with open pores, which enabled rapid ion ingress and egress, and the high effective surface area of the MOF allowed the uptake and release of a large number of electrolyte ions during charge-discharge. By combining this NiCo-MOF cathode with a highly porous carbon (PC) anode (derived from the naturally grown and abundantly available bio-waste, namely, palm kernel shells), the resulting PC//NiCo-MOF supercapacitor using an aqueous potassium hydroxide (KOH) electrolyte delivered a capacitance of 134 F g-1, energy and power densities of 24 Wh kg-1 and 0.8 kW kg-1 at 1 A g-1, respectively, over an operational voltage window of 1.6 V. By employing thin interlayers of PC coated over a Whatman filter paper (PC@FP), the modified supercapacitor configuration of PC/PC@FP//PC@FP/NiCo-MOF delivered greatly enhanced performance. This cell delivered a capacitance of 520 F g-1 and an energy density of 92 Wh kg-1, improved by nearly 4-fold, compared to the analogous supercapacitor without the interlayers (at the same power and current densities and voltage window), thus evidencing the role of the cost-effective, electrically conducting porous carbon interlayers in amplifying the supercapacitor's energy storage capabilities. Further, illumination of white light-emitting diodes (LEDs) using a three-series configuration and the photocharging of this supercapacitor with a solution-processed solar cell are also demonstrated. The latter confirms its ability to function as a stand-alone power supply system for electronic/computing devices, which can even operate under medium lighting conditions.

A poly(3,4-propylenedioxythiophene)/carbon micro-sphere-bismuth nanoflake composite and multifunctional Co-doped graphene for a benchmark photo-supercapacitor.

Efficient storage of sunlight in the form of charge is accomplished by designing and implementing a photo-supercapacitor (PSC) with a novel, cost-effective architecture. Sulfur (S)- and nitrogen (N)-doped graphene particles (SNGPs) are incorporated in a TiO2/CdS photoanode. The beneficial effects of SNGPs such as the high electrical conductance promoting fast electron transfer to TiO2, a suitably positioned conduction band that maximizes charge separation, and its' ability to absorb red photons translate into a power conversion efficiency of 9.4%, for the champion cell. A new composite of poly(3,4-propylenedioxythiophene)/carbon micro-sphere-bismuth nanoflakes (PProDOT/CMS-BiNF) is integrated with the photoanode to yield the PSC. The photocurrent produced under 1 sun irradiance is directed to the supercapacitor, wherein, the synergy between the faradaic and electrical double layer charge accumulation mechanisms of PProDOT and CMS-BiNF bestows storage parameters of an areal capacitance of 104.6 mF cm-2, and energy and power densities of 9 µW h cm-2 and 0.026 mW cm-2. An overall photo-conversion and storage efficiency of 6.8% and an energy storage efficiency of 72% exhibited by the PSC are much superior to those delivered by a majority of the PSCs reported in the literature on the otherwise highly efficient perovskite solar cell or the expensive Ru dye based solar cells.

A photoanode with plasmonic nanoparticles of earth abundant bismuth for photoelectrochemical reactions.

A wide range of technologies has been developed for producing hydrogen economically and in greener ways. Photoelectrochemical water splitting using photoelectrodes submerged in a bath electrolyte forms a major route of hydrogen evolution. The efficacy of water splitting is improved by sensitizing metal oxide photoelectrodes with narrow bandgap semiconductors that efficiently absorb sunlight and generate and transport charge carriers. Here we show that the efficiencies of photocurrent generation and photoelectrochemical hydrogen evolution by the binary TiO2/Sb2S3 anode increase by an order of magnitude upon the incorporation of the earth-abundant plasmonic bismuth nanoparticles into it. The ternary electrode TiO2/Bi nanoparticle/Sb2S3 illuminated with sunlight provides us with a photocurrent density as high as 4.21 mA cm-2 at 1.23 V, which is fourfold greater than that of the binary electrode and tenfold greater than that of pristine TiO2. By using bismuth nanoparticles, we estimate the incident photon to current conversion efficiency at 31% and solar power conversion efficiency at 3.85%. Here the overall impact of bismuth nanoparticles is attributed to increases in the open-circuit voltage (860 mV), which is by expediting the transfer of photogenerated electrons from Sb2S3 nanoparticles to the TiO2 electrode, and short-circuit current (9.54 mA cm-2), which is by the plasmonic nearfield effect. By combining the cost-effective plasmonic bismuth nanoparticles with the narrow bandgap Sb2S3 on the TiO2 electrode, we develop a stable, ternary photoanode and accomplish high-efficiency photocurrent generation and hydrogen evolution.

Carbon@Tellurium Nanostructures Anchored to a Si Nanowire Scaffold with an Unprecedented Liquid-Junction Solar Cell Performance.

Silicon nanowire (SiNW) arrays offer a range of exciting opportunities, from maximizing solar spectrum utilization for high-performance liquid-junction solar cells (LJSCs) to functioning as potential micro-supercapacitors in the near future. This work, contrasting strongly with the previously reported studies on SiNW-based LJSCs where electron-conducting nanoparticles of Pt or Au were employed to achieve high efficiencies, aims at tethering relatively inexpensive, hole-conducting, and photoresponsive carbon-coated tellurium nanorods (C@TeNRs) to SiNWs in the quest to achieve an outstanding solar cell performance. A SiNW LJSC (control cell) with a SiNWs/Br-, Br2/carbon-fabric architecture delivers a power conversion efficiency (PCE) of 4.8%. Further, by anchoring C@TeNRs, along the lengths of SiNWs via electrophoresis, a PCE of ∼11.6% is attained for a C@TeNRs@SiNWs/Br-, Br2/carbon-fabric-based LJSC. The multifunctionality of C@Te comes to the fore in this cell where (1) the p-type (hole) conducting nature of C@Te ensures efficient charge separation by rapidly collecting holes from SiNWs (and suppresses recombination), (2) the C@TeNRs are also photoresponsive and increase light-harvesting, and (3) the C coating restricts the chemical corrosion and photo-oxidation of SiNWs and the Te core by the acidic electrolyte, thereby improving the cell's operational lifetime. This LJSC also serves as an effective stand-alone energy-storage device giving an improved areal specific capacitance of 1605 µF cm-2 (at 1 mA cm-2). This study unravels the pivotal role played by C@TeNRs in controlling the performance of SiNW-based LJSCs.

Quantum Dot Donor-Polymer Acceptor Architecture for a FRET-Enabled Solar Cell.

Forster resonance energy-transfer (FRET)-based solution-processed solar cell is fabricated with cadmium sulfide (CdS) as the energy donor and poly[ N-9'-heptadecanyl-2,7-carbazole- alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) as the energy acceptor. Carbon dots (C-dots) deposited on carbon fabric are applied as a counter electrode. Although electron injection from CdS to PCDTBT is energetically disfavored, evidences for energy transfer between the two components of the cell are obtained in terms of FRET parameters with the relative quantum yield of donor CdS quantum dots (QDs) being ∼0.3, a Forster radius of ∼3.7 nm, and an energy-transfer efficiency of ∼55%. Power conversion efficiency (PCE) of the TiO2/PCDTBT cell without the donor is 0.23% and when coupled with donor CdS QDs, the ensuing TiO2/PCDTBT/CdS cell experiences a 23 time increment in PCE, reaching 5.3%. The complete FRET cell: TiO2/PCDTBT/CdS/ZnS-S2--C-dots/C-fabric produces a PCE of 7.42%, under 1 sun illumination. External quantum efficiency studies reveal an enhanced spectral response spanning from 300 to 670 nm, with 300 and 175% increases attained for the FRET-enabled TiO2/PCDTBT/CdS/ZnS photoanode compared with the TiO2/PCDTBT photoanode over the blue and green-red portions of the solar spectrum.

Nickel cobaltite@poly(3,4-ethylenedioxypyrrole) and carbon nanofiber interlayer based flexible supercapacitors.

Binder free flexible symmetric supercapacitors are developed with nickel cobaltite micro-flower coated poly(3,4-ethylenedioxypyrrole) (NiCo2O4@PEDOP) hybrid electrodes. The free standing films of carbon nano-fibers (CNFs), synthesized by electrospinning, were sandwiched between the NiCo2O4@PEDOP hybrid and the electrolyte coated separators on both sides of the cells. The CNF film conducts both ions and electrons, and confines the charge at the respective electrodes, to result in an improved specific capacitance (SC) and energy density compared to the analogous cell without the CNF interlayers. A high SC of 1775 F g-1 at a low current density of 0.96 A g-1 and an SC of 634 F g-1 achieved at a high current density of 38 A g-1 coupled with an SC retention of ∼95% after 5000 charge-discharge cycles in the NCO@PEDOP/CNF based symmetric supercapacitor, are performance attributes superior to those achieved with NCO and NCO/CNF based symmetric cells. The PEDOP coating serves as a highly conductive matrix for the NCO micro-flowers and also undergoes doping/de-doping during the charge-discharge, thus amplifying the overall supercapacitor response, compared to the individual components. The CNF interlayers show reasonably high ion-diffusion coefficients for K+ and OH- propagation, implying facile pathways available for the movement of ions across the cross-section of the cell, and they also serve as ion reservoirs. The electrode morphologies remain unaffected by cycling in the presence of the CNF interlayer. LED illumination and a largely unaltered charge storage response were achieved in a mutli-cell configuration, proving the potential for this approach in practical applications.

Enhanced photoelectrochemical activity of Co-doped ß-In2S3 nanoflakes as photoanodes for water splitting.

This work is primarily focused on indium sulfide (ß-In2S3) and cobalt (Co)-doped ß-In2S3 nanoflakes as photoanodes for water oxidation. The incorporation of cobalt introduces new dopant energy levels increasing visible light absorption and leading to improved photo-activity. In addition, cobalt ion centers in ß-In2S3 act as potential catalytic sites to promote electro-activity. 5 mol% Co-doped ß-In2S3 nanoflakes when tested for photoelectrochemical water splitting exhibited a photocurrent density of 0.69 mA cm-2 at 1.23 V, much higher than that of pure ß-In2S3.

Metal Oxide Interlayer for Long-Lived Lithium-Selenium Batteries.

A lithium-selenium (Li-Se)-alkali activated carbon hybrid cell with a tungsten oxide interlayer is implemented for the first time. The Se hybrid at a Se loading of 70 % in the full Li-Se cell delivers a large reversible capacity of 625 mA h gSe -1 , in comparison with 505.8 mA h gSe -1 achieved for the pristine Se cell. This clearly shows the advantage of the carbon in improving the capacity of the Li-Se cell. A tungsten oxide interlayer is drop-cast over the battery separator to further circumvent the issues of polyselenide dissolution and shuttle, which cause severe capacity fading. The oxide layer conducts Li ions, as evidenced from the Li-ion diffusion coefficient of 4.2×10-9  cm2 s-1 , and simultaneously blocks the polyselenide crossover, as it is impermeable to polyselenides, thereby reducing the capacity fading with cycling. The outcome of this unique approach is reflected in the reversible capacities of 808 and 510 mA h gSe -1 achieved for the Li-oxide@separator/Se-alkali activated carbon cell before and after 100 cycles, respectively, thus demonstrating that carbon and oxide can efficiently restrict the capacity fading and improve the performances of Li-Se cells.

Bifunctional Photo-Supercapacitor with a New Architecture Converts and Stores Solar Energy as Charge.

Photo-supercapacitors (PSCs) combine functions of energy harvesting and storage in a single device, and in this study, a new architecture for a PSC is designed and implemented. Cadmium sulfide (CdS) quantum dots/hibiscus (hb) dye co-sensitized TiO2 is used as the solar cell. Poly(3,4-ethylenedioxypyrrole) (PEDOP)@manganese dioxide (MnO2) is employed as the counter electrode (CE) for the solar cell and also as the electrodes for the symmetric supercapacitor. The two ends of a long flat current collector support two spatially separated PEDOP@MnO2 coatings, which serve as the CEs for the TiO2/hb/CdS photoanode and yet another PEDOP@MnO2 electrode in sandwich configurations. In this cell, under 1 sun (100 mW cm-2) illumination, the TiO2/hb/CdS photoanode undergoes charge separation and by channeling the photocurrent to the PEDOP@MnO2 electrodes, the symmetric cell part is charged to a voltage of 0.72 V. The PSC delivers a specific capacitance of 183 F g-1, an energy density of 13.2 Wh kg-1, and a power density of 360 W kg-1 at a discharge current density of 1 A g-1. During the self-discharge process, PEDOP@MnO2-based PSC retains a voltage of 0.72 V up to 500 s and maintains a stable voltage of 0.5 V thereafter. The TiO2/hb/CdS photoanode with the PEDOP@MnO2 CE in an aqueous polysulfide-silica gel electrolyte delivers a power conversion efficiency of 6.11%. This demonstration of a novel PSC opens up opportunities to develop new architectures for efficiently combining energy conversion and storage.

Dual function of molybdenum sulfide/C-cloth in enhancing the performance of fullerene nanosheets based solar cell and supercapacitor.

Quantum dot solar cells (QDSCs) with hexagonal fullerene nanosheets (C60-NS) embedded in a titanium oxide/cadmium sulfide (TiO2/CdS) photoanode coupled with a carbon-cloth (C-cloth) coated with molybdenum sulfide (MoS2) counter electrode (CE) are studied for the first time. C60-NS due to a favorable work function of 4.57 eV and a conductance of 1.44 µS, enable faster electron injection from the conduction band of cadmium sulfide to the current collector, in contrast to the bulk fullerene based TiO2/CdS solar cell. The champion cell with the TiO2/C60-NS/CdS photoanode and a MoS2/C-cloth CE exhibits a high power conversion efficiency of 5.6%, greater by ∼14% relative to its' analogue cell with bulk fullerene. A large area cell of 1 cm2 dimensions with TiO2/C60-NS/CdS gives a PCE of 2.9%. The effect of MoS2 in improving the efficiency of the cell with a TiO2/C60-NS/CdS photoanode is realized in terms of enhanced electrocatalytic activity for polysulfide reduction, and lower charge transfer resistance at the polysulfide/CE interface compared to a cell with the same photoanode but having pristine carbon-cloth as the CE. The ability of MoS2 for catalyzing the oxidized polysulfide species at the CE and C60-NS for improving the charge collection at the photoanode serve as indicators for their wider utilization in solar cells. It also serves as a good supercapacitor material. A MoS2/C-cloth based symmetric cell exhibits a specific capacitance of 645 F g-1 at 2 A g-1, which shows its' potential for energy storage as well. By integrating the QDSC and the supercapacitor, the resulting integrated device acquires a photovoltage of 0.7 V, under 1 sun illumination.

New Antimony Selenide/Nickel Oxide Photocathode Boosts the Efficiency of Graphene Quantum-Dot Co-Sensitized Solar Cells.

A novel assembly of a photocathode and a photoanode is investigated to explore their complementary effects in enhancing the photovoltaic performance of a quantum-dot solar cell (QDSC). While p-type nickel oxide (NiO) has been used previously, antimony selenide (Sb2Se3) has not been used in a QDSC, especially as a component of a counter electrode (CE) architecture that doubles as the photocathode. Here, near-infrared (NIR) light-absorbing Sb2Se3 nanoparticles (NPs) coated over electrodeposited NiO nanofibers on a carbon (C) fabric substrate was employed as the highly efficient photocathode. Quasi-spherical Sb2Se3 NPs, with a band gap of 1.13 eV, upon illumination, release photoexcited electrons in addition to other charge carriers at the CE to further enhance the reduction of the oxidized polysulfide. The p-type conducting behavior of Sb2Se3, coupled with a work function at 4.63 eV, also facilitates electron injection to polysulfide. The effect of graphene quantum dots (GQDs) as co-sensitizers as well as electron conduits is also investigated in which a TiO2/CdS/GQDs photoanode structure in combination with a C-fabric CE delivered a power-conversion efficiency (PCE) of 5.28%, which is a vast improvement over the 4.23% that is obtained by using a TiO2/CdS photoanode (without GQDs) with the same CE. GQDs, due to a superior conductance, impact efficiency more than Sb2Se3 NPs do. The best PCE of a TiO2/CdS/GQDs-nS2-/Sn2--Sb2Se3/NiO/C-fabric cell is 5.96% (0.11 cm2 area), which, when replicated on a smaller area of 0.06 cm2, is seen to increase dramatically to 7.19%. The cell is also tested for 6 h of continuous irradiance. The rationalization for the channelized photogenerated electron movement, which augments the cell performance, is furnished in detail in these studies.

Solar cells with PbS quantum dot sensitized TiO2-multiwalled carbon nanotube composites, sulfide-titania gel and tin sulfide coated C-fabric.

Novel approaches to boost quantum dot solar cell (QDSC) efficiencies are in demand. Herein, three strategies are used: (i) a hydrothermally synthesized TiO2-multiwalled carbon nanotube (MWCNT) composite instead of conventional TiO2, (ii) a counter electrode (CE) that has not been applied to QDSCs until now, namely, tin sulfide (SnS) nanoparticles (NPs) coated over a conductive carbon (C)-fabric, and (iii) a quasi-solid-state gel electrolyte composed of S2-, an inert polymer and TiO2 nanoparticles as opposed to a polysulfide solution based hole transport layer. MWCNTs by virtue of their high electrical conductivity and suitably positioned Fermi level (below the conduction bands of TiO2 and PbS) allow fast photogenerated electron injection into the external circuit, and this is confirmed by a higher efficiency of 6.3% achieved for a TiO2-MWCNT/PbS/ZnS based (champion) cell, compared to the corresponding TiO2/PbS/ZnS based cell (4.45%). Nanoscale current map analysis of TiO2 and TiO2-MWCNTs reveals the presence of narrowly spaced highly conducting domains in the latter, which equips it with an average current carrying capability greater by a few orders of magnitude. Electron transport and recombination resistances are lower and higher respectively for the TiO2-MWCNT/PbS/ZnS cell relative to the TiO2/PbS/ZnS cell, thus leading to a high performance cell. The efficacy of SnS/C-fabric as a CE is confirmed from the higher efficiency achieved in cells with this CE compared to the C-fabric based cells. Lower charge transfer and diffusional resistances, slower photovoltage decay, high electrical conductance and lower redox potential impart high catalytic activity to the SnS/C-fabric assembly for sulfide reduction and thus endow the TiO2-MWCNT/PbS/ZnS cell with a high open circuit voltage (0.9 V) and a large short circuit current density (∼20 mA cm-2). This study attempts to unravel how simple strategies can amplify QDSC performances.

Identifying the charge generation dynamics in Cs+-based triple cation mixed perovskite solar cells.

Triple cation based perovskite solar cells offer enhanced moisture tolerance and stability compared to mixed perovskites. Slight substitution of methyl ammonium or formamidinium cation by cesium (Cs+), was also reported to eliminate halide segregation due to its smaller size. To elucidate the device kinetics and understand the role of the Cs, we undertook different modes of scanning probe microscopy and electrochemical impedance spectroscopy (EIS) experiments. Kelvin probe force microscopy revealed that the incorporation of the Cs cation increases the contact potential difference (CPD), this CPD further increases when Spiro-OMeTAD is used as a hole transport material. The current at the nanoscale level shows improvement with Cs inclusion and further enhancement by the Spiro-OMeTAD deposition, studied under light illumination, which supports the high photocurrent density obtained from the cells. EIS demonstrates that in a triple cation environment, reduced carrier recombination at the TiO2/perovskite interface was also obtained which in turn allow us to achieve a higher Voc value.

Stability, Scale-up, and Performance of Quantum Dot Solar Cells with Carbonate-Treated Titanium Oxide Films.

A novel yet simple approach of carbonate (CBN) treatment of TiO2 films is performed, and quantum dot solar cells (QDSCs) with high power conversion efficiencies (PCEs), reasonably good stabilities, and good fill factors (FFs) are fabricated with TiO2-CBN films. The ability of carbonate groups to passivate defects or oxygen vacancies of TiO2 is confirmed from a nominally enhanced band gap, a lowered defect induced fluorescence intensity, an additional Ti-OH signal obtained after carbonate decomposition, and a more capacitive low frequency electrochemical impedance behavior achieved for TiO2-CBN compared to untreated TiO2. A large area QDSC of 1 cm2 with a TiO2-CBN/CdS/Au@PAA (poly(acrylic acid)) photoanode delivers an enhanced PCE of 4.32% as opposed to 3.03% achieved for its analogous cell with untreated TiO2. Impedance analysis illustrates the role of carbonate treatment in increasing the recombination resistance at the photoanode/electrolyte interfaces and in suppressing back-electron transfer to the electrolyte, thus validating the superior PCE achieved for the cell with carbonate-treated TiO2. QDSCs with the configuration TiO2-CBN/CdS/Au@PAA-polysulfide/SiO2 gel-carbon-fabric/WO3-x and active areas of 0.2-0.3 cm2 yield efficiencies in the range of 5.16 to 6.3%, and the average efficiency of the cells is 5.9%. The champion cell is characterized by the following photovoltaic parameters: JSC (short circuit current density), 11.04 mA cm-2; VOC (open circuit voltage), 0.9 V; FF, 0.63; and PCE, 6.3%. Stability tests performed on this cell show that dark storage has a less deleterious effect on cell performance compared to extended illumination. In dark, the PCE of the cell dropped from 5.69 to 5.52%, and under prolonged continuous irradiance of 5 h, it decreased from 5.91 to 4.83%. A scaled-up QDSC with the same architecture of 4 cm2 size showed a PCE of 1.06%, and the demonstration of the lighting of a LED accomplished using this cell exemplifies that this cell can be used for powering electronic devices that require low power.

Titanium oxide morphology controls charge collection efficiency in quantum dot solar cells.

Charge transfer at the TiO2/quantum dots (QDs) interface, charge collection at the TiO2/QDs/current collector (FTO or SnO2:F) interface, and back electron transfer at the TiO2/QDs/S2- interface are processes controlled by the electron transport layer or TiO2. These key processes control the power conversion efficiencies (PCEs) of quantum dot solar cells (QDSCs). Here, four TiO2 morphologies, porous nanoparticles (PNPs), nanowires (NWs), nanosheets (NSHs) and nanoparticles (NPs), were sensitized with CdS and the photovoltaic performances were compared. The marked differences in the cell parameters on going from one morphology to the other have been explained by correlating the shape, structure and the above-described interfacial properties of a given TiO2 morphology to the said parameters. The average magnitudes of PCEs follow the order: NWs (5.96%) > NPs (4.95%) > PNPs (4.85%) > NSHs (2.5%), with the champion cell based on NWs exhibiting a PCE of 6.29%. For NWs, an optimal balance between the fast photo-excited electron injection to NWs at the NW/CdS interface, the high resistance offered at the TiO2 NW/CdS/S2- interfaces to electron recombination with the oxidized electrolyte or with the holes in CdS, the low electron transport resistance in NWs, and low dark currents, yields the highest efficiency due to directional unhindered transport of electrons afforded by the NWs. For NSHs, electron trapping in the two dimensional sheets, and a high electron recombination rate prevent the effective transfer of electrons to FTO, thus reducing short circuit current density significantly, resulting in a poor performance. This study provides a deep understanding of charge transfer, transport and collection processes necessary for the design of efficient QDSCs.

Cesium power: low Cs+ levels impart stability to perovskite solar cells.

Towards increasing the stability of perovskite solar cells, the addition of Cs+ is found to be a rational approach. Recently triple cation based perovskite solar cells were found to be more effective in terms of stability and efficiency. Heretofore they were unexplored, so we probed the Cs/MA/FA (cesium/methyl ammonium/formamidinium) cation based perovskites by X-ray photoelectron spectroscopy (XPS) and correlated their compositional features with their solar cell performances. The Cs+ content was found to be optimum at 5%, when incorporated in the (MA0.15FA0.85)Pb(I0.85Br0.15)3 lattice, because the corresponding device yielded the highest fill factor compared to the perovskite without Cs+ and with 10% Cs+. XPS studies distinctly reveal how Cs+ aids in maintaining the expected stoichiometric ratios of I : Pb2+, I : N and Br : Pb2+ in the perovskites, and how the valence band (VB) edge is dependent on the Cs+ proportion, which in turn governs the open circuit voltage. Even at a low content of 5%, Cs+ resides deep within the absorber layer, and ensures minimum distortion of the VB level (compared to 0% and 10% Cs+ perovskites) upon Ar+ sputtering, thus allowing the formation of a stable robust material that delivers excellent solar cell response. This study which brings out the role of Cs+ is anticipated to be of paramount significance to further engineer the composition and improve device performances.