Liquid-junction Solar Cells Research Articles

Thermoelectric and photovoltaic properties of 12-BaBi2S4

In this report, we have investigated the structure and properties of the 12-BaBi2S4. A single crystal X-ray diffraction study shows that the 12-BaBi2S4 crystallizes in the hexagonal crystal system (space group = P63/m) with refined lattice parameters of a = b = 25.2687(10) Å, c = 4.1859(2) Å, and formula unit = Z = 12 at room temperature. The structure contains fifteen crystallographic independent sites, including three Ba, four Bi, and eight types of S atoms. A phase pure polycrystalline sample of 12-BaBi2S4 was synthesized by heating stoichiometric amounts of BaCO3 and Bi2O3 under a CS2 atmosphere. The phase pure sample is found to be a semiconductor with a direct bandgap of 1.3(1) eV. The polycrystalline 12-BaBi2S4 exhibits ultra-low thermal conductivity values, varying from 0.47 Wm−1K−1 at 323 K to 0.43 Wm−1K−1 at 773 K. The sample shows high values of the Seebeck coefficient (S = −300 μV/K to −210 μV/K) in the 323 K–773 K range with poor electrical conductivity values. The negative sign of the S implies that the sample is a n-type semiconductor. DFT studies of the 12-BaBi2S4 also predict semiconducting properties. We have explored the 12-BaBi2S4 sample for photovoltaic (PV) applications by fabricating a liquid junction solar cell, TiO2/CdS/12-BaBi2S4/Sn2−/S2−/MWCNTs@Ni, which delivered an efficiency enhanced by ∼12 % to the control cell based on sole CdS as the photo-sensitizer. Theoretical electronic structure calculations suggest the semiconducting nature of the 12-BaBi2S4 in agreement with the optical absorption and electrical resistivity studies.

A Review on the Applicability of Luminescent Phosphors and Effective Positioning in Dye‐Sensitized Solar Cells for Enhanced Performance and Stability

The narrow range of solar light absorption facilitated by the photoactive organic dyes has been restricting the significant development, and large‐scale applications of dye‐sensitized solar cells (DSSC). The major problem that limits the power conversion efficiency (PCE) of DSSC is the limitations of the organic dyes (light absorbers in DSSC) to absorb beyond the visible region of solar spectrum that resulting in lower PCE (≈13%) as compared with the commercialized technologies. Hence, the focus on developing efficient strategies to harvest the ultraviolet and infrared light regions of the solar spectrum and effective conversion into the absorption limit of dyes and thereby increasing the device performance and stability is the emerging technological development in DSSCs. Rare earth ion‐doped upconversion (UC) and downconversion (DC) phosphors are the most promising solutions for the prevalent issues of the liquid junction solar cells. This review will focus on the emerging strategies for the PCE enhancement of DSSC with UC and DC materials. An exclusive review on the facile approach of simultaneous usage of both the UC and DC phosphors and the effective positioning of these spectral conversion phosphors, to achieve highly stable DSSCs with superior PCE is provided.

(Invited) Molecular Reaction Imaging of Charge Transport in MoS2 Nanoflake Photoelectrodes

Transition metal dichalcogenides (TMD) such as WSe2 and MoS2 are highly efficient and stable light absorbers in TMD∣I−,I3 −∣Pt liquid junction solar cells. It is generally accepted that TMD crystals with a large fraction of exposed edge sites exhibit lower power conversion efficiencies (PCEs) than apparently smooth crystals. However, one open question is why does the PCE vary significantly from one crystal to another? Answering this critical question could lead to robust syntheses for high quality and uniform TMD samples. In this work, we apply nanoscale photoelectrochemical microscopy techniques to study n-type TMD nano flake∣I−,I3 −∣Pt cells. Using a combination of near-diffraction-limited photocurrent mapping and molecular reaction imaging techniques, we reveal a previously hidden surface recombination process: photogenerated holes in hidden p-type domains travel micron-scale distances parallel to the solid/liquid interface and preferentially react with iodide at step-edges. The overall efficiency of the nanoflake, as evidenced from whole nanoflake-level photoelectrochemical measurements, is dictated by the size, efficiency, and location of n- and p-type domains. These results provide a unifying view of efficiency losses in smooth TMD photoelectrodes and open the possibility to design electrode architectures that leverage the long-range lateral charge transport property for photoelectrocatalysis.

Molecular Reaction Imaging of a Surface Recombination Process Explains Performance Variation Among Smooth MoS2 Photoelectrodes

Transition metal dichalcogenides (TMD) such as WSe2 and MoS2 are highly efficient and stable light absorbers in TMD∣I−,I3 −∣Pt liquid junction solar cells. It is generally accepted that TMD crystals with a large fraction of exposed edge sites exhibit lower power conversion efficiencies (PCEs) than apparently smooth crystals. However, one open question is why does the PCE vary significantly from one crystal to another? Answering this critical question could lead to robust syntheses for high quality and uniform TMD samples. In this work, we apply nanoscale photoelectrochemical microscopy techniques to study n-type TMD nanoflake∣I−,I3 −∣Pt cells. Using a combination of near-diffraction-limited photocurrent mapping and molecular reaction imaging techniques, we reveal a previously hidden surface recombination process: photogenerated holes in hidden p-type domains travel micron-scale distances parallel to the solid/liquid interface and preferentially react with iodide at step-edges. The overall efficiency of the nanoflake, as evidenced from whole nanoflake-level photoelectrochemical measurements, is dictated by the size, efficiency, and location of n- and p-type domains. These results provide a unifying view of efficiency losses in smooth TMD photoelectrodes and open the possibility to design electrode architectures that leverage the long-range lateral charge transport property for photoelectrocatalysis.

CoS Nanoflakes on Textured Silicon Coupled with Antimony-Decorated Tungsten Oxide for Efficient Liquid Junction Solar Cells

CoS Nanoflakes on Textured Silicon Coupled with Antimony-Decorated Tungsten Oxide for Efficient Liquid Junction Solar Cells

Photophysics and photovoltaic properties of Zn-alloyed Ag-In-S quantum dots sensitized solar cells

Quantum dots (QDs) have attracted attention for use in photovoltaic applications. However, till now, QDs sensitized liquid junction solar cells (QDSCs) are primary concentrated on binary QDs that contain toxic elements which limit their practical applications in regarding of environmental issues. Hence, the study of less-toxic ternary such as AgInS2 (AIS) and CuInS2 (CIS) or core/shell AIS/ZnS and CIS/ZnS QDs with high power conversion efficiency (PCE) is the most common way for commercial applications. Although significant improvement has been realized for AIS (CIS) QDSCs by overgrowth of wide bandgap ZnS to form quasi type-I core/shell structure for eliminating surface trapping defects where the PCE is comparable or even better than toxic QDs, simultaneously the shell could also cause impeding electron injection from QDs to metal oxide matrix (TiO2) and hole scavenge. For resolving this problem, diffusion of Zn2+ into QDs forming alloyed QDs is a better strategy to improve the conductivity and thus the PCE owing to alloyed QDs could not only reduce the density of trap defects but also regulate the bandgap and contribute to electron injection. Herein, the highly luminescent heavy-metal free and hydrophilic Ag-In-S-Zn alloyed QDs with broad light harvesting range to near infrared (NIR) were synthesized as effective sensitizer for constructing QDSCs, where the optimal PCE of 3.12% was achieved. Moreover, surface passivation by deposition of ZnS layer over the sensitized electrode was also primarily studied to decrease the QDs/electrolyte/TiO2 interface recombination and a champion PCE of 3.78% was obtained.

Heterostructure of CsPbBr3-CdS perovskite quantum dots for enhanced stability and charge transfer

CsPbBr3quantum dot (PQD) was interfaced with CdS quantum dot (QD), via modified hot injection method to form a heterostructure, acrosswhose interface a significantly enhanced charge transfer is demonstrated. Formation of heterostructure (with retention of individual characteristics) was evidenced by various spectroscopy, microscopy and DFT tools. The heterostructure is observed to be much stable (one acting as pseudo protecting layer for the other) with enhanced electron lifetime and favorable band energy offset. CdS QDs reduce the strain within PQDs by holding them in a matrix kind of a structure, thus passivating the uncoordinated sites. It thus holds potential to be exploited for faster charge transfer in solar cell and other optoelectronic applications. Nature of PL quenching with growth of CdS QDs on PQDs, suggest energy transfer.The optimized formulation was also applied to liquid junction solar cells as sensitizers just to evidence the better electron transport, and charge separation properties.

Solution-processed Cd-substituted CZTS nanocrystals for sensitized liquid junction solar cells

The Earth-abundant kesterite Cu2ZnSnS4 (CZTS) exhibits outstanding structural, optical, and electronic properties for a wide range of optoelectronic applications. However, the efficiency of CZTS thin-film solar cells is limited due to a range of factors, including electronic disorder, secondary phases, and the presence of anti-site defects, which is a key factor limiting the Voc. The complete substitution of Zn lattice sites in CZTS nanocrystals (NCs) with Cd atoms offers a promising approach to overcome several of these intrinsic limitations. Herein, we investigate the effects of substituting Cd2+ into Zn2+ lattice sites in CZTS NCs through a facile solution-based method. The structural, morphological, optoelectronic, and power conversion efficiencies (PCEs) of the NCs synthesized have been systematically characterized using various experimental techniques, and the results are corroborated by first-principles density functional theory (DFT) calculations. The successful substitution of Zn by Cd is demonstrated to induce a structural transformation from the kesterite phase to the stannite phase, which results in the bandgap reduction from 1.51 eV (kesterite) to 1.1 eV (stannite), which is closer to the optimum bandgap value for outdoor photovoltaic applications. Furthermore, the PCE of the novel Cd-substituted liquid junction solar cell underwent a four-fold increase, reaching 1.1%. These results highlight the importance of substitutional doping strategies in optimizing existing CZTS-based materials to achieve improved device characteristics.

Easy-to-fabricate high efficiency silicon nanowires solar cell modified by CdTe and zinc tetraphenyl porphyrin nanostructures

Liquid junction solar cell (LJSC) with vertically silicon nanowires (SiNWs) as the primary photosensitizer, co-sensitized with luminescent and narrow gap CdTe nanoparticles, and cuboidal microstructures of zinc tetraphenyl porphyrin (ZnTPP) dye offers broad and intense visible light absorption that translates into a maximum power conversion efficiency (PCE) of 9.09%, when combined with a polymeric gel of a I2/I− redox couple as the hole transport material and a counter electrode (CE) of poly(3,4-ethyelenedioxythiophene) doped with imide ions (PEDOT-N(CF3SO2)2), under 1 sun irradiance. The p-type CdTe efficiently scavenges holes from SiNWs and simultaneously allows the passage of photoexcited electrons from ZnTPP to SiNWs via electrical conduction thus imparting an enhanced solar cell performance. Co-sensitization also supresses back electron transfer effectively, as is inferred from a ~68% enhancement in PCE compared to SiNWs alone. Optimization of the CE entailed the evaluation of the effect of dopant anion: imide versus dicyanamide in PEDOT, and revealed that the presence of macro-cracks in the polymer surface, a deeper work function, and a lower electrical conductance are the shortcomings of the dicyanamide doped PEDOT and reduce the overall PCE, compared to imide. This study brings out how by judicious choice of photoanode and CE components, efficient, stable and easy-to-assemble LJSCs can be developed.

Efficient Charge Separation Enabled by N-Doped Graphene Quantum Dots and PCDTBT for a High-Performance Silicon Nanowire Solar Cell

Light absorption by n-silicon nanowires (SiNWs) grown by a chemical etching method is augmented by tethering photoresponsive and highly luminescent nitrogen-doped graphene quantum dots (N-GQDs) and poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) to a SiNW array. The resultant N-GQDs@PCDTBT@SiNW photoanode affords a wide, continuous, and intense absorption band spanning from ∼350 to 1200 nm wavelength range, enabling maximum light uptake, with a work function of ∼4.74 eV, deep enough to not serve as a charge-trapping state. Under illumination, efficient charge separation in this ternary composite is ensured by the p-type semiconducting nature of N-GQDs with a shallow valence band (VB) that allows for rapid hole extraction from the VBs of SiNW and PCDTBT and their rapid relay to the bromide ions in the electrolyte. This is simultaneously accompanied by fast, excited electron injection from N-GQDs and PCDTBT to the SiNW via a cascade process, thus minimizing back electron transfer to the tribromide ions. When the N-GQDs@PCDTBT@SiNW photoanode is coupled with a highly electrocatalytic and electrically conductive multiwalled carbon nanotube (MWCNT)@C-fabric counter electrode and a bromine/bromide electrolyte, a power conversion efficiency of 13.18% is achieved for this liquid junction solar cell, which is significantly enhanced compared to that of the SiNW/HBr,Br2/C-fabric cell (4.37%). The roles of N-GQDs, PCDTBT, and MWCNTs are independently quantified to explain the observed solar cell performance.

Improved performance of quantum dot-sensitized solar cells by full-spectrum utilization

One of important factors for improving the power conversion efficiency (PCE) of quantum dot-sensitized solar cells is to enhance the utilization of sunlight. Herein, we modified the wavelength range of incident sunlight from the counter electrode (CE) side to investigate the photoelectric performance of solar cells. The effect of illuminating CuS and Cu2S CE with different light ranges (including non-illumination, UV–visible light, NIR light and full-spectrum light) on cell performance was investigated. It has been shown that illuminating from both sides of cell induce substantial increase in PCE, and a 42.8% enhancement in PCE compared with that irradiating from the photoanode side has been achieved with a champion PCE of 5.6% (Voc = 0.6 V, Jsc = 21.7 mA cm−2) based on CuS CE. This strategy focuses on the neglected problem of light utilization of the CE, and provides a direction for realizing full-spectrum absorption of liquid-junction solar cells.

An investigation of recombination processes in liquid junction solar cells by transient photocurrent measurements

In this research, TiO2-RGO composites were produced using the hydrothermal method. These composite structures were used in the phonoanodes of liquid junction solar cells. This study examines recombination mechanisms in liquid junction quantum dot sensitized solar cells (QDSSCs) with reduced graphene oxide (RGO) doped TiO2 nanocomposite photoanodes, using the transient photo-current analysis method. RGO doped composite photoanode liquid junction solar cells exhibit electron lifetimes up to four times longer than pure TiO2 photoanode. This increase indicates that new electron transport paths emerged within the composite thanks to RGO, that a significant reduction was achieved in the back-transfer of electrons and that recombination mechanisms were suppressed.

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.

Photoactive Porphyrin‐Based Metal‐Organic Framework Nanosheets

5,10,15,20‐Tetrakis[4′‐(terpyridinyl)phenyl]porphyrin and 5,10,15,20‐tetrakis[4′‐(terpyridinyl)‐1,1′‐biphenyl]porphyrin were used as building blocks for the construction of metal–organic framework (MOF) nanosheets with visible light absorption by utilizing the Langmuir–Blodgett technique. Moreover, the MOF‐nanosheet‐modified ITO electrodes were placed into liquid junction solar cells, and the photoconversion efficiencies of these cells were evaluated upon visible light irradiation. In the present work, the layer number of the nanosheets and the inclusion of C60 as guest have been demonstrated to be responsible for improved cell photoelectrical conversion by enhancing absorption and charge transfer, respectively.

Laser Annealing Improves the Photoelectrochemical Activity of Ultrathin MoSe2 Photoelectrodes.

Understanding light-matter interactions in transition-metal dichalcogenides (TMDs) is critical for optoelectronic device applications. Several studies have shown that high intensity light irradiation can tune the optical and physical properties of pristine TMDs. The enhancement in optoelectronic properties has been attributed to a so-called laser annealing effect that heals chalcogen vacancies. However, it is unknown whether laser annealing improves functional properties such as photocatalytic activity. Here, we show that high intensity supra band gap illumination improves the photoelectrochemical activity of MoSe2 nanosheets for iodide oxidation in indium doped tin oxide/MoSe2/I-, I3-/Pt liquid junction solar cells. Ensemble-level photoelectrochemical measurements show that, on average, illuminating MoSe2 thin films with 1 W/cm2 532 nm excitation increases the photoelectrochemical current by 142% and shifts the photocurrent response to more favorable (negative) potentials. Scanning photoelectrochemical microscopy measurements reveal that pristine bilayer (2L)-MoSe2, trilayer (3L)-MoSe2, and multilayer-thick nanosheets are initially inactive for iodide oxidation. The light treatment activates 2L-MoSe2 and 3L-MoSe2 materials, and the activation process initiates at the edge sites. The photocurrent enhancement is more significant for 2L-MoSe2 than for 1L-MoSe2. Multilayer-thick MoSe2 remains inactive for iodide oxidation even after the laser treatment. Our microscopy measurements reveal that the laser-induced enhancement effect depends critically on MoSe2 layer thickness. X-ray photoelectron spectroscopy measurements further show that the laser treatment oxidizes Mo(IV) species that are initially associated with Se vacancies. Ambient oxygen fills the Se vacancies and removes trap states, thereby increasing the overall photogenerated carrier collection efficiency. To the best of our knowledge, this work represents the first report on using laser to enhance the photoelectrocatalytic properties of few-layer-thick TMDs. The simple and rapid laser annealing procedure is a promising strategy to tune the reactivity of TMD-based photoelectrochemical cells for electricity and chemical fuel production.

Effect of Capping-Agents on Performance of Copper Nickel Tin Sulfide (CNTS) Nanocrystals Based Solar Cells

In recent years, colloidal semiconductor nanocrystals based solar cells have achieved photo-conversion efficiency closed to 12% which has triggered renewed interest to undertake fundamental investigation on these materials. Among many prospective candidates, quaternary chalcogenides viz. Copper Zinc Tin Sulfide/Selenides (CZTS) and its analogs have been tested extensively due to its high absorption coefficient near 1.1-1.5eV, low elemental cost, non-toxic nature and ability to form alloy structures, without apparent phase segregation. All these characteristics make them very attractive candidate to investigate them for solar cell applications. Their composition dependent band-edge parameters give further opportunity to form tandem heterojunction devices which would absorb broad spectrum of light and give the possibility to push the performance towards betterment. In many such investigation the capping agents used in the preparation of nanocrystals have assumed to be mute candidate in performance of the solar cells. However, our preliminary investigation on copper nickel tin sulfide (CNTS) nanocrystals based solar cell revealed that the nature of capping agents is also an important parameter and impact the solar cell performance. Herein, we report the preparation of CNTS nanocrystals and demonstrated the effect of capping agents on the performance of solar cells. To prepare CNTS nanocrystals, hot-injection method have been used. Two variants have been prepared by varying capping agents; long-chain oleylamine capped CNTS (OLA-CNTS) and short chain Mercaptopropionic acid (MPA) capped CNTS (MPA-CNTS). These were well characterized by UV-Vis-NIR, XRD, Raman, AFM, TEM, FESEM, and EDAX. All these characterizations confirm the formation single phase CNTS. Cyclic voltammetry investigation have been performed on CNTS nanocrystals to estimate the conduction and valence band edge parameters as a function of composition. For the first time, CNTS liquid junction solar cell with an architecture; FTO/TiO2/CdS-CNTS/ZnS/S-/Sn--/CuS/Se/FTO have been prepared. Solar cell prepared out of OLA-CNTS gave very poor power conversion efficiency. While, similar solar cell constructed out of MPA-CNTS displayed better performance having the efficiency and the fill factor in the order of 1.25 % and 0.380, respectively. Furthermore, an electrochemical impedance spectroscopy (EES) measurements revealed that MPA-CNTS has relatively low charge transfer resistance than OLA-CNTS. This property has been attributed to the poor performance of OLA-CNTS. Further investigations to optimize this material and device architecture would expected to increase the efficiency. Figure 1

Selenium Nanoparticle-decorated Silicon Nanowires with Enhanced Liquid-Junction Photoelectrochemical Solar Cell Performance

Selenium nanoparticles decorated silicon nanowires (Se NPs@Si NWs) electrode is applied as a photoanode in a liquid junction photoelectrochemical (PEC) solar cell for the first time. Upon illumination, the Se NPs anchored along the axial length of Si NWs allow fast hole extraction at the radial Se/Si junctions, due to the p-type conduction nature of Se NPs thus enhancing electron-hole separation, and simultaneously increase the population of photoexcited electrons in Si NWs through light scattering that amplifies the effective light absorption of Si NWs. These attributes of Se NPs result in a power conver-sion efficiency (PCE) of 7.03% for the Se NPs@Si NWs based liquid junction solar cell encompassing a Br-/Br2 electrolyte and a carbon fabric counter electrode. This PCE is greater by 43% than that of the analogous Si NWs based cell. Se NPs are photo-conducting due to facile hole-propagation that occurs particularly along the c-axis of trigonal Se NPs with a hexago-nal crystal structure, and size effects improve the optical path length, factors that lead to a significantly improved perfor-mance. Compared to Pt or Au NPs that have been explored previously in combination with Si NWs, where their roles are distinctively different, Se NPs here, are not only more cost effective, and easy to synthesize on a large-scale, but they enable an improvement in PCE of Si NWs, by relying on unique mechanisms. Optical-, structural-, PEC-, and impedance- studies furnish a deep understanding of the phenomena involved in yielding a superior performing liquid junction PEC solar cell based on the Se NPs@Si NWs photoanode.

Efficient MOF-Sensitized Solar Cells Featuring Solvothermally Grown [100]-Oriented Pillared Porphyrin Framework-11 Films on ZnO/FTO Surfaces.

Owing to their abilities to assemble and organize a large number of redox and photoactive components in highly ordered periodic fashion, crystalline porous metal-organic frameworks (MOFs) have the potential to execute myriad complex functions, including charge transport and light to electrical energy conversion when the required conditions are fulfilled. Herein, we demonstrate an unprecedented spontaneous solvothermal growth of precisely [100]-oriented pillared porphyrin framework-11 (PPF-11) films featuring vertically aligned Zn-tetrakis(4-carboxyphenyl)porphyrin (ZnTCPP) walls and horizontally aligned 2,2'-dimethyl-4,4'-bipyridine beams attached to annealed ZnO-fluorine-doped tin oxide (FTO) surfaces and their remarkable photovoltaic performance in liquid-junction solar cells. The [100]-oriented PPF-11/ZnO-FTO photoanodes displayed excellent photovoltaic response (short-circuit current ( JSC): 4.65 mA/cm2, open-circuit voltage ( VOC): 470 mV, power conversion efficiency: 0.86%) that easily outperformed all control devices as well as previously reported porphyrin and Ru(bpy)32+-based visible light-harvesting MOFs with 10-1000 times greater photocurrent density and 2-375 times higher efficiency. The superior photovoltaic behavior of [100]-oriented PPF-11/ZnO films compared to epitaxially grown MOF thin films on insulating self-assembled monolayers and drop-cast PPF films with different orientations can be attributed to several factors, including better charge separation, transport, and injection capabilities of the former. The noncatenated PPF-11 was able to host electron-deficient C60 guests, filling in nearly half of its cavities and engage them in ZnTCPP/C60 charge-transfer interaction. However, the C60-doped PPF-11/ZnO films displayed much weaker photovoltaic response than undoped [100]-oriented PPF-11/ZnO films presumably due to exclusion of I-/I3- electrolyte from the C60-occupied cavities and the inability of isolated C60 guests to support long-range charge movement.

Iron Doped CdSe Films with Improved Photosensitivity and Stability for Use in a Liquid Junction Solar Cell

In the present investigation, transition metal Fe has been introduced in low levels in the CdSe matrix to formulate CdFeSe films for application in photoelectrochemical solar cells. Periodic voltammetry was employed to deposit the ternary films on FTO glass. Spectral characteristics, morphology, and composition of the matrices were determined by the respective physiochemical methods. The band gap energies of CdFeSe thin films were increased with the increase of Fe content. Electrochemical impedance spectroscopy, chronoamperometry, and photosensitivity of the film matrices were studied. In order to derive the functional parameters at the anode–electrolyte interface, the cell configuration, FTO/CdFeSe/S2––Sx2–/Pt, coupled with calomel reference electrode was used. Anodic stripping voltammetry was employed to investigate the inherent stability of the film matrices. The performance screening of the films ultimately indicates the best output in terms of photoconversion efficiency (η, %), fill factor (FF, %), a...

Role of Photogenerated Iodine on the Energy-Conversion Properties of MoSe2 Nanoflake Liquid Junction Photovoltaics.

Transition metal dichalcogenides (TMDs) such as MoSe2 and WSe2 are efficient materials for converting solar energy to electrical energy in photoelectrochemical photovoltaic cells. One limiting factor of these liquid junction solar cells is that photogenerated oxidation products accumulate on the electrode surface and decrease the photocurrent efficiency. However, it is unclear where the reaction products accumulate on the electrode surface and how they impact the local photoelectrochemical response. This open question is especially important for the structurally heterogeneous TMD nanoflake thin-film electrodes that are promising for large-area solar energy conversion applications. Here, we use a single-nanoflake photoelectrochemical and Raman microscopy approach to probe how the photogenerated I2/I3- products impact the photocurrent collection efficiency and the onset potential in MoSe2-nanoflake|I-/I2|Pt photoelectrochemical solar cells. We observed localized I2/I3- deposition on all types of MoSe2 nanoflake surface motifs, including basal planes, perimeter edges, and interior step edges. Illuminated nanoflake spots with the highest photocurrent collection efficiency are the first to be limited by I2/I3- formation under high-intensity illumination. Interestingly, I2/I3- formation occurs on illuminated surface spots that have the lowest photocurrent onset potential for iodide oxidation, corresponding to the highest open circuit voltage ( VOC). The VOC shifts could be attributed to variations in the surface reaction kinetics or doping density across the nanoflake. Our results highlight important limiting factors of nanoflake thin-film TMD liquid junction photovoltaics under concentrated solar illumination intensities.