Bilayer Solar Cells Research Articles

Exploring the NiPcTs-Si nanoheterojunction as a bilayer solar cell: theoretical and experimental analysis

Exploring the NiPcTs-Si nanoheterojunction as a bilayer solar cell: theoretical and experimental analysis

Cu-Doped Sb2Se3 Thin-Film Solar Cells Based on Hybrid Pulsed Electron Deposition/Radio Frequency Magnetron Sputtering Growth Techniques

In recent years, research attention has increasingly focused on thin-film photovoltaics utilizing Sb2Se3 as an ideal absorber layer. This compound is favored due to its abundance, non-toxic nature, long-term stability, and the potential to employ various cost-effective and scalable vapor deposition (PVD) routes. On the other hand, improving passivation, surface treatment and p-type carrier concentration is essential for developing high-performance and commercially viable Sb2Se3 solar cells. In this study, Cu-doped Sb2Se3 solar devices were fabricated using two distinct PVD techniques, pulsed electron deposition (PED) and radio frequency magnetron sputtering (RFMS). Furthermore, 5%Cu:Sb2Se3 films grown via PED exhibited high open-circuit voltages (VOC) of around 400 mV but very low short-circuit current densities (JSC). Conversely, RFMS-grown Sb2Se3 films resulted in low VOC values of around 300 mV and higher JSC. To enhance the photocurrent, we employed strategies involving a thin NaF layer to introduce controlled local doping at the back interface and a bilayer p-doped region grown sequentially using PED and RFMS. The optimized Sb2Se3 bilayer solar cell achieved a maximum efficiency of 5.25%.

Performance analyses of highly efficient inverted all-perovskite bilayer solar cell

Numerical simulation of an all-perovskite bilayer solar cell has been conducted by the SCAPS-1D. The presented structure employs MAPbI3 as a relatively wide bandgap (1.55 eV) top absorber and FA0.5MA0.5Pb0.5Sn0.5I3 as a narrow bandgap (1.25 eV) bottom absorber. The viability of the proposed design is accomplished in two steps. First, to validate this study, two inverted solar cells in standalone conditions are simulated and calibrated to fit previously reported state-of-the-art results. Second, both these devices are appraised for the bilayer configuration to boost their performances. Affecting parameters such as the thickness of perovskite absorbers, the work function of front and rear contacts, and the effect of temperature have been studied because solar cells are temperature-sensitive devices, and also carrier concentration and their mobility get overwhelmingly influenced as temperature increases. It is manifested that using bilayer structures could easily widen the absorption spectrum to the near-infrared region and significantly enhance the performance of the device which is mainly affected by the thickness of the FA0.5MA0.5Pb0.5Sn0.5I3 layer. Also, it has been found that the work function of the front contact has a prominent role with its optimal values being above 5 eV. Finally, the optimized inverted all-perovskite bilayer solar cell delivers a power conversion efficiency of 24.83%, fill factor of 79.4%, open circuit voltage of 0.9 V, and short circuit current density of 34.76 mA/cm2 at 275 K and a thickness of 100 nm and 600 nm for MAPbI3 and FA0.5MA0.5Pb0.5Sn0.5I3, respectively.

Simulation study of CsPbIxBr1-x and MAPbI3 heterojunction solar cell using SCAPS-1D

The perovskite solar cells are attaining maximum efficiency but lagging in stability as compared with other solar cells. The consistent use of hybrid organic–inorganic materials in PSC poses greatest hurdle in the path of stability. To overcome this problem the attention of research community, is diverted from methyl ammonium based perovskite solar cells to cesium (Cs) based perovskite solar cell. To enhance the efficiency of PSCs further, effective absorption of solar-spectrum by the multi-layer will allow the maximum utilization of spectrum and in turn it will increase the efficiency of the resulting Perovskite Solar Cell (PSC). Here, we have analyzed the efficiencies of single, double and triple absorber layers PSCs. Initially we have simulated and studied the performance of two CsPbI2Br and CsPbIBr2 based single-junction perovskite solar cell. Then we have simulated a PSC with CsPbI2Br and CsPbIBr2 as the two absorber layers and have optimized the performance of bilayer solar cell. Finally, we simulated a triple layer PSC have used the combination of CsPbI2Br, CsPbIBr2 and MAPbI3 as absorber layers. The bilayer and triple layer PSCs are optimized with respect to different variables i.e., absorber layer thickness, defect density and interface defect density in all three PSCs. In this study we achieved a remarkable efficiency of 29.92%, 20.62% and 7% efficiency in case of triple layer solar cell, in case of bilayer solar cell and in case of single-junction PSC respectively. Thus, well aligned multiple absorber layers in PSC will provide the future pathways for highly efficient PSCs.

Design of a CH3NH3PbI3/CsPbI3-based bilayer solar cell using device simulation

With lead-based light harvesters, perovskite solar cells (PSCs) have an efficiency of approximately 25.5%, making them a viable photovoltaic technology. The selection of the absorber materials for PSC in this work are (i) Cesium lead iodide (CsPbI3) with a 1.73eV bandgap as the first absorber layer, this halide imparts higher stability to perovskite solar cells (ii) CH3NH3PbI3 (MAPbI3) with a bandgap of 1.55eV is selected as the second absorber layer as this material provides better efficiency to the perovskite solar cells. SCAPS-1D simulation software is used to perform an efficiency analysis of perovskite-perovskite CsPbI3/MAPbI3 bilayer solar cell. For efficiency optimization of the perovskite-perovskite bilayer solar cell, we have tried to calibrate seven parameters of the cell. These parameters are (i & ii) selection of the electron and hole transport material (iii, iv & v) variation in the: defect density of bulk material, doping concentration and the thickness of absorber layers, (vi) variation in work function of front electrode (vii) varying interface defect density. After optimization, the efficiency (η) of bilayer PSC is estimated to be 33.54%. The other PV parameters observed in optimal efficiency condition are open-circuit voltage (VOC) = 1.34V, short-circuit current density (JSC) = 27.45 mA/cm2 and fill factor (FF) = 90.49%. The CsPbI3/MAPbI3 bilayer perovskite solar cell efficiency is roughly double the efficiency of single junction CsPbI3 or MAPbI3 PSC. Our analysis observed that the variation in the doping and defect density of narrow bandgap material profoundly impacts the efficiency of perovskite-perovskite bilayer solar cells compared to the wide bandgap material.

Janus transition-metal dichalcogenides heterostructures for highly efficient excitonic solar cells

The emergence of two-dimensional semiconductors opens up new avenues for efficient, ultrathin, and high-quality heterojunction solar cells. Herein, based on first-principles calculations, we present the optoelectronic features of a series of experimentally feasible 2D Janus transition metal dichalcogenides monolayers in a configured van der Waals nanostructure. The assembled heterostructures are energetically, dynamically, and mechanically stable, forming type-II band alignment p–n heterojunctions. Thus, the spatial separation of the photo-generated electron–hole pairs is achieved. In the MoXY-WXY (X, Y= S, Se, Te; and X≠Y) vdW heterostructures, the WXY monolayer acts as a good donor material for the acceptor MoXY material. The minimal conduction band offset among constituent monolayers, ideal donor bandgap, and superior optical absorption make Janus TMDCs vdW nanostructures excellent candidates for photovoltaic conversion in 2D excitonic solar cells. On the other hand, the maximum power conversion efficiencies of designed MoSSe-WSSe, MoSTe-WSTe, and MoSeTe-WSeTe bilayer solar cells are calculated to be 17.90%, 21.82%, and 22.99%, respectively. Our findings point out the potential use of here investigated heterostructures in nanophotonics and high-performance excitonic solar cells.

Modeling of Ag incorporated Sb[formula omitted](S[formula omitted]Se[formula omitted])[formula omitted] bi-layer devices: Enhanced bi-layer absorber configuration

In this contribution, we proposed Ag incorporated Sb2(SxSe1−x)3 bi-layer solar cells by modeling and simulation to optimize the absorber layer. Firstly, as the sulfur composition increases, we have investigated simple single-layer devices with the absorber film of each AgSb(SxSe1−x)3 and Sb2(SxSe1−x)3 as a frame of reference. Secondly, the impact of sulfur composition on bi-layer devices has been studied with two different absorber configurations such as Sb2(SxSe1−x)3/AgSb(SxSe1−x)3 and AgSb(SxSe1−x)3/Sb2(SxSe1−x)3. Compared with any single-layer devices, the absorber configuration of AgSb(S0.4Se0.6)3/Sb2(S0.4Se0.6)3 bi-layers shows best performance at the sulfur composition, x = 0.4. This is caused by the reduced effective Schottky barrier (by 126 mV) at the back contact, improving the roll-over effect by 4.3 times at 1 V. The resulting efficiency is 18.6 %, Voc (778.9 mV), Jsc (37.2 mA/cm2), and FF (64.0 %). Once the devices with highest efficiency and the optimal sulfur composition are identified, a set of different device parameters have been studied to optimize these bi-layer devices further. With AgSb(S0.4Se0.6)3/Sb2(S0.4Se0.6)3 bi-layer devices, the result from various doping concentration of each bi-layers indicates that doping concentration of AgSb(S0.4Se0.6)3 is responsible for Jsc, while the doping concentration of Sb2(S0.4Se0.6)3 dictates Voc under certain doping concentration of AgSb(S0.4Se0.6)3 (approximately 1 × 1015/cm2). The best efficiency is 21.4% with Voc (822 mV), Jsc (38.1 mA/cm2), and FF (68.4%).

Tailoring the Nature of Interface States in Efficient and Stable Bilayer Organic Solar Cells by a Transfer‐Printing Technique

AbstractBulk heterojunction organic solar cells (BHJ‐OSCs) are designed to overcome inefficient charge generation and limited exciton diffusion of organic semiconductors. However, there are some disadvantages involving inherent voltage losses, microstructure control, and operational instability. Bilayer solar cells (BL‐OSCs) without mixed regions are free from these problems and offer a platform to explore the photophysical processes at the donor–acceptor interface. Here, a breakthrough for n‐i‐p BL‐OSCs in charge generation efficiency is reported. A gradual adjustment of the molecular interface orientation of the polymer donor (PM6) is accompanied by the evolution of charge‐transfer states and Forster energy transfer. Besides, less recombination losses and superior morphological stability of BL‐OSCs are achieved at a PCE comparable to that of BHJ‐OSCs with similar layer thickness. This investigation confirms the feasibility of manufacturing BL‐OSCs by a transfer printing method and provides a versatile architecture to study fundamental interface phenomena in OSCs independent from microstructure disorder.

Rubrene single crystal solar cells and the effect of crystallinity on interfacial recombination.

Single crystal studies provide a better understanding of the basic properties of organic photovoltaic devices. Therefore, in this work, rubrene single crystals with a thickness of 250 nm to 1000 nm were used to produce an inverted bilayer organic solar cell. Subsequently, polycrystalline rubrene (orthorhombic, triclinic) and amorphous bilayer solar cells of the same thickness as single crystals were studied to make comparisons across platforms. To investigate how single crystal, polycrystalline (triclinic-orthorhombic) and amorphous forms alter the charge carrier recombination mechanism at the rubrene/PCBM interface, light intensity measurements were carried out. The light intensity dependency of the JSC, VOC and FF parameters in organic solar cells with different forms of rubrene was determined. Monomolecular (Shockley Read Hall) recombination is observed in devices employing amorphous and polycrystalline rubrene in addition to bimolecular recombination, whereas the single crystal device is weakly affected by trap assisted SRH recombination due to reduced trap states at the donor acceptor interface. To date, the proposed work is the only systematic study examining transport and interface recombination mechanisms in organic solar cells produced by different structure forms of rubrene.

Efficiency of exciton dissociation at the interface between a conjugated polymer and an electron acceptor with consideration for a two-dimensional arrangement of interfacial dipoles

• ET from the donor to acceptor creates interfacial dipoles at a D-A interface. • A hole interacts with its geminate electron and with interfacial dipoles. • A dipolar layer changes the potential energy of the hole and electron. • The dissociation probability of an electron-hole pair is calculated. Exciton dissociation at the interface between a conjugated polymer as an electron donor (D) and a fullerene derivative as an acceptor (A) is often considered in the dipole model that suggests existence of the dipolar layer between D and A materials. In the current article, we calculate the dissociation probability of excitons in the dipole model assuming a two-dimensional arrangement of the interfacial dipoles at a D-A interface. We find that the dipolar layer between D-A materials can radically alter the energy of the Coulomb attraction between an optically generated electron and its geminate hole. We show that the calculated dissociation probability of electron-hole pairs is in agreement with experimental field dependences of photocurrents reported previously for a bilayer solar cell consisting of C 60 as an electron acceptor and a well ordered conjugated polymer as an electron donor.

Tuning the band gap and carrier concentration of titania films grown by spatial atomic layer deposition: a precursor comparison.

Spatial atomic layer deposition retains the advantages of conventional atomic layer deposition: conformal, pinhole-free films and excellent control over thickness. Additionally, it allows higher deposition rates and is well-adapted to depositing metal oxide nanofilms for photovoltaic cells and other devices. This study compares the morphological, electrical and optical properties of titania thin films deposited by spatial atomic layer deposition from titanium isopropoxide (TTIP) and titanium tetrachloride (TiCl4) over the temperature range 100–300 °C, using the oxidant H2O. Amorphous films were deposited at temperatures as low as 100 °C from both precursors: the approach is suitable for applying films to temperature-sensitive devices. An amorphous-to-crystalline transition temperature was observed for both precursors resulting in surface roughening, and agglomerates for TiCl4. Both precursors formed conformal anatase films at 300 °C, with growth rates of 0.233 and 0.153 nm s−1 for TiCl4 and TTIP. A drawback of TiCl4 use is the HCl by-product, which was blamed for agglomeration in the films. Cl contamination was the likely cause of band gap narrowing and higher defect densities compared to TTIP-grown films. The carrier concentration of the nanofilms was found to increase with deposition temperature. The films were tested in hybrid bilayer solar cells to demonstrate their appropriateness for photovoltaic devices.

Numerical study of organic graded bulk heterojunction solar cell using SCAPS simulation

The graded bulk heterojunction (GBHJ) organic solar cell (OSC), with an active layer of donor-blend-acceptor structure, has recently paid much attention in developing the performance of OSCs. In this work, a numerical simulation has been performed for a GBHJ solar cell using SCAPS simulator to provide some design guidelines for this type of OSC. Firstly, the validation of the simulation is done by comparing the simulation with experimental results. Then, a comparative study is performed between the presented GBHJ with conventional bulk heterojunction (BHJ) and bi-layer solar cells. Simulation results indicate that GBHJ has the highest power conversion efficiency (PCE) of 10.15%, while BHJ has the highest collection efficiency (ζcoll) of 96.71%. The GBHJ performance is optimized by inspecting each layer individually and the interfacial trap states. It has been found that the main layer, having the most crucial impact on the performance, is the blend layer and its optimum thickness is 70 nm. Further, an improvement of the performance of GBHJ is achieved by using other candidates of non-fullerene acceptors (NFAs) with higher reported blend mobilities. A short circuit current density (Jsc) of 19.88 mA/cm2, open circuit voltage (Voc) of 0.798 V, fill factor (FF) of 78.68%, PCE of 12.49% and ζcoll of 95.12% is obtained.

Highly improvement in efficiency of Cu(In,Ga)Se2 thin film solar cells

PurposeThe purpose of this study is to design and optimize copper indium gallium selenide (CIGS) thin film solar cells.Design/methodology/approachA novel bi-layer CIGS thin film solar cell based on SnS is designed. To improve the performance of the CIGS based thin film solar cell a tin sulfide (SnS) layer is added to the structure, as back surface field and second absorbing layer. Defect recombination centers have a significant effect on the performance of CIGS solar cells by changing recombination rate and charge density. Therefore, performance of the proposed structure is investigated in two stages successively, considering typical and maximum reported trap density for both CIGS and SnS. To achieve valid results, the authors use previously reported experimental parameters in the simulations.FindingsFirst by considering the typical reported trap density for both SnS and CIGS, high efficiency of 36%, was obtained. Afterward maximum reported trap densities of 1 × 1019 and 5.6 × 1015 cm−3 were considered for SnS and CIGS, respectively. The efficiency of the optimized cell is 27.17% which is achieved in CIGS and SnS thicknesses of cell are 0.3 and 0.1 µm, respectively. Therefore, even in this case, the obtained efficiency is well greater than previous structures while the absorbing layer thickness is low.Originality/valueHaving results similar to practical CIGS solar cells, the impact of the defects of SnS and CIGS layers was investigated. It was found that affixing SnS between CIGS and Mo layers causes a significant improvement in the efficiency of CIGS thin-film solar cell.

Bicontinuous network of electron donor-acceptor composites achieved by additive-free sequential deposition for efficient polymer solar cells

We report that sequential deposition of a highly crystalline polymer donor and a soluble fullerene acceptor leads to a well-defined interpenetrating network and enhanced power conversion efficiencies in bilayer polymer solar cells. Even without the use of solvent additives, layered thin films of poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di(2-octyldodecyl)-2,2’; 5′,2’’; 5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD) and [6,6]-phenyl C71-butyric acid methyl ester (PC71BM), as electron donor and acceptor materials, respectively, showed bicontinuous networks similar to those of a PffBT4T-2OD:PC71BM bulk-heterojunction (BHJ) thin film processed with 1,8-diiodooctane (DIO) as a solvent additive. Transmission electron microscopy results confirmed the BHJ-like morphology of the bilayered PffBT4T-2OD/PC71BM thin films. Bilayer solar cells fabricated without the DIO additive produced a power conversion efficiency of η ≈ 7.65%, which is even higher than that of a BHJ solar cell fabricated with the DIO additive (η ≈ 7.04%). These results demonstrate that a highly crystalline polymer donor and an electron-accepting small molecule can be a good combination for efficient bilayer polymer solar cells.

ZrS3/MS2 and ZrS3/MXY (M[dbnd]Mo, W; X, Y[dbnd]S, Se, Te; X ≠ Y) type-II van der Waals hetero-bilayers: Prospective candidates in 2D excitonic solar cells

Excellent photovoltaic abilities in a 2D excitonic solar cell based on staggered type-II van der Waals (vdW) hetero-bilayers comprising of semiconducting ZrS3 monolayer and monolayers of MS2 & MXY (MMo, W; X, YS, Se, Te; X ≠ Y) are reported herewith, using DFT-D2 and HSE06 functional. Studies on vdW hetero-bilayers of MX3/MX2 and MX3/M'Y2 have so far been conveniently avoided on account of their large lattice mismatch. The present work is the first attempt to address such hetero-bilayers constituted by monolayers of transition metal dichalcogenides and trichalcogenides. The nature of the band edges in ZrS3 and MS2 monolayers induces high electron and hole mobility in these individual monolayers, respectively, which has been combined synergistically in the hetero-bilayers consisting of them. The Power Conversion Efficiency (PCE) in ZrS3/MoS2, ZrS3/WS2, ZrS3/MoSeTe, ZrS3/WSTe, and ZrS3/WSeTe hetero-bilayers, calculated within the Anderson-limit, are found to reach as high as ~12%, 8%, 16%, 14%, and 14% respectively. The PCE of the hetero-bilayers reported herewith are much higher than the efficiency in MoS2/p-Si heterojunction solar cells (5.23%) and comparable to that of the theoretically proposed PCBM fullerene/BCN system (10–20%) and g-SiC2-based systems (12–20%) and the recently predicted TiNF/TiNBr (18%), TiNCl/TiNBr (19%), TiNF/TiNCl (22%) bilayer solar cell systems.

Bilayer polymer solar cells prepared with transfer printing of active layers from controlled swelling/de-swelling of PDMS

Herein, we demonstrate a facile method for transferring thin films to achieve polymer solar cells having stacked structures. By controlling the swelling/de-swelling properties of Polydimethylsiloxane (PDMS) via solvent treatment, we formed uniform organic films upon the PDMS surface and then transferred them to target substrates. We prepared bilayer and graded bilayer structures after transferring indene-C60 bis-adduct (ICBA) and ratio-controlled poly(3-hexylthiophene) (P3HT:ICBA) blends, respectively, onto the P3HT layer. The optimal graded bilayer solar cell exhibited a power conversion efficiency (PCE) of 5.13% an impressive value compared with that obtained for the corresponding bilayer cell (3.67%). We attribute this enhancement in PCE to the greater number of junction interfaces and the balanced carrier transfer properties. This residue-free and place-lift-off transferring method appears to have great promise in the solution processing of multilayer stacked thin film optoelectronics.

Degradation pathways in standard and inverted DBP-C70 based organic solar cells

Achieving long-term stability in organic solar cells is a remaining bottleneck for the commercialization of this otherwise highly appealing technology. In this work, we study the performance and stability differences in standard and inverted DBP/C70 based organic solar cells. Differences in the charge-transfer state properties of inverted and standard configuration DBP/C70 solar cells are revealed by sensitive external quantum efficiency measurements, leading to differences in the open-circuit voltages of the devices. The degradation of standard and inverted solar cell configurations at ISOS aging test conditions (ISOS-D-3 and ISOS-T-3) was investigated and compared. The results indicate that the performance drop in the small molecule bilayer solar cells is less related to changes at the D-A interface, suggesting also a pronounced morphological stability, and instead, in the case of inverted cells, dominated by degradation at the electron transport layer (ETL) bathocuproine (BCP). Photoluminescence measurements, electron-only-device characteristics, and stability measurements show improved exciton blocking, electron transport properties and a higher stability for BCP/Ag ETL stacks, giving rise to inverted devices with enhanced performance and device stability.

Conjugated Polyions Enable Organic Photovoltaics Processed from Green Solvents

This paper describes the design, synthesis, and optical and electronic properties of two conjugated polymers CPIZ-B and CPIZ-T that incorporate closed-shell cations into their conjugated backbones, balanced by anionic pendant groups. The zwitterionic nature of the polymers renders them soluble in and processable from polar, protic solvents to form semiconducting films that are not doped. These unique properties are confirmed by absorption and electron paramagnetic resonance spectroscopy. The energies of the unoccupied states respond to the tritylium moieties in the conjugated backbone, while the occupied states respond to the electron-donating ability of the uncharged, aromatic units in the backbone. Films cast from 80:20 HCOOH/H2O by volume show good electron mobilities, enabling a photovoltaic effect in proof-of-concept, bilayer solar cells.

Impact of Phosphorescent Sensitizers and Morphology on the Photovoltaic Performance in Organic Solar Cells

AbstractPhosphorescent sensitizers (PSs) are considered as a promising alternative for increasing the internal quantum efficiency (IQE) in organic solar cells (OSCs). By converting short‐lifetime singlet into long‐living triplet excitons, enhanced exciton diffusion and dissociation have been reported previously. However, only a limited increase in the OSC performance has been achieved. In this work, the interplay of the PS with both singlet and triplet excitons within organic blends is examined using kinetic Monte Carlo simulations including a comprehensive model of excitonic processes. Different morphologies of the conventional P3HT:PCBM solar cell are simulated, and the excitonic properties and their influence on the photovoltaic performance under doping are studied. The use of phosphorescent sensitization ensures high intersystem crossing and enlarges the diffusion length. An increase in the IQE of 34% is observed for a bilayer OSC. The increasing decay of triplets in proximity to the PS due to a strong spin‐orbit coupling limits the IQE. Unlike expected, triplet‐triplet annihilation does not provide a significant loss of excitons. A doped planar‐mixed molecular heterojunction outperforms an undoped bulk‐heterojunction OSC due to the enhanced exciton diffusion. A further study of optimal PS parameters predicts an increase in the IQE within bilayer solar cells by about 100%.

Broadband Light Harvesting Enhancement of MoS2/Graphene Bilayer Solar Cell via Metal Nanosquare Arrays-Dielectric-Metal Structure

Low absorptance of transition metal dechalcongenides has limited their potential applications in photon detection and light harvesting, which motivates the quest for new approaches to improve the absorption in these systems. Here, we demonstrate a broadband and polarization-independent metal nanosquare arrays-dielectric-metal stucture to improve the light absorption in the solar cells based on bilayer of MoS2/graphene. By performing three-dimensional electromagnetic simulations, it is revealed that the optical absorption in the monolayer MoS2 can be significantly enhanced to be over 60% in a broad wavelength range due to the combined effects of localized surface plasmonic resonance (LSPR), LSPR coupling and cavity resonance. Furthermore, the short current density of the bilayer solar cell reaches a high value of 15.7 mA/cm2, which is about 8.3 times that of the bilayer solar cell without the metal nanosquare arrays-dielectric-metal stucture structure. These results may provide useful guidance for future photovoltaics, energy conversion, and light harvesting devices.