Planar Solar Cells Research Articles

Spectral Characteristics of Cascade Photoelectric Converters on the Base of Physically Real Tunnel Homogeneous Semiconductor Structures

Spectral photoresponse of homogeneous cascade (multijunction) photoelectric converterеs (PC) on the basis of real tunnel nano-structures prepared by precision epitaxial growth technologies upon base single PC - monocrystalline substrate with diffusion layers, and optimized for particular (specific) radiation wavelengths have been studied. Planar high-voltage solar cells are one of the such structures application. For cascade silicon PCs, photoresponse dependences on spectral charge carrier collection efficiency in the base PC, semiconductor structure design and fabrication technology parameters have been analyzed.

High-quality perovskite films via post-annealing microwave treatment

The crystalline quality of the perovskite film plays a key role in improving the optoelectronic properties and the performance of planar perovskite hybrid solar cells (PSCs).

Binary organic spacer-based quasi-two-dimensional perovskites with preferable vertical orientation and efficient charge transport for high-performance planar solar cells

The (PEA0.8BA0.2)2MA3Pb4I13 binary spacer Q-2D perovskite device yields a high power conversion efficiency of 15.7%.

3D low toxicity Cu–Pb binary perovskite films and their photoluminescent/photovoltaic performance

The 3D low-toxic Cu–Pb binary perovskite films with improved geometric symmetry and typical 2 μm grain size have been prepared, which can achieve a six fold increase in PL intensity and a PCE of 5.1% with suppressed hysteresis for planar solar cells.

Open-Circuit Voltages Exceeding 1.26 V in Planar Methylammonium Lead Iodide Perovskite Solar Cells

We demonstrate open-circuit voltages exceeding 1.26 V for inverted planar CH3NH3PbI3 solar cells fabricated using a combination of lead acetate and PbCl2 precursors leading to smooth films and large grain sizes. Surface recombination is suppressed by careful optimization of the PTAA hole transport and PCBM electron transport layers. Suppression of bulk and surface recombination is verified by absolute photoluminescence measurements with external quantum efficiencies of ∼5% in complete cells. In addition, we find exceptionally long photoluminescence lifetimes in full cells and in layer stacks involving one or two contact layers. Numerical simulations reveal that these long photoluminescence lifetimes are only possible with extremely low recombination velocities at the interfaces between absorber and contact materials.

Controlled growth of SbSI thin films from amorphous Sb2S3 for low-temperature solution processed chalcohalide solar cells

We report a simple solution processing method for fabricating low-temperature SbSI solar cells. The method consists of two steps: the formation of amorphous Sb2S3 and its transformation to SbSI. A pure SbSI phase with a high crystallinity was obtained at a low temperature of 200 °C. In addition, the SbSI morphology was controlled by tuning the input ratio of SbCl3:thiourea and a dense film was obtained at a ratio of 1:1.3. A planar SbSI solar cell thus-fabricated exhibits a short-circuit current density of 5.45 mA cm−2, an open-circuit voltage of 0.548 V, and a fill factor of 0.31, corresponding to a power conversion efficiency of 0.93% under a 100 mW cm−2 illumination condition.

Tin Perovskite Solar Cells Are Back in the Game

This issue of Joule features an article by Wang et al. that demonstrates that high-efficiency tin-based solar cells can be realized by the formation of a heterostructure consisting of two-dimensional (2D) and three-dimensional (3D) perovskites based on phenylethylammonium tin iodide (PEA2SnI4) and formamidinium tin iodide (FASnI3), respectively, forming from the study of the PEA2(FA)n-1SnnI3n+1 system. The authors convincingly show that these self-assembled heterostructures can be manipulated and ordered sequentially by chemical means, thus providing a new avenue for further improving the perovskite solar cell technology.

Mixed halide perovskite light emitting solar cell

We demonstrate that the halide perovskite planar solar cells with the architecture of ITO/PEDOT:PSS/Perovskite/PCBM/LiF/Al show a switchable dual operation of descent photovoltaic and quite bright electroluminescence in visible range. In our experiments, the active layer is made of a mixed halide perovskite (MAPbBr2I) and the device is properly cycled upon light and bias exposure. We argue that this curious effect of switchable double functionality between solar cell and light-emitting device in one architecture is caused by photoinduced segregation in the perovskite. It is shown that the bright red electroluminescence at low voltage of ∼ 2 (3) eV appears only after cycling the device in PV regime. On the other hand, electroluminescence operation also effects the following PV mode. This effect is caused by redistribution of photoactivated ions I-/Br- and their vacancies during photoexcitation in PV regime.

Alkali Metals Doping for High‐Performance Planar Heterojunction Sb2S3 Solar Cells

Sb2S3 as a stable light harvesting material has received increasing attention for solar cell applications. To improve the device efficiency, much effort has been put into the materials synthesis, interfacial engineering, and device structure design. Here, it is demonstrated that doping of alkali metal (Li, Na, K, Rb, Cs) ions essentially affects the morphological, crystal, optical and electrical properties of Sb2S3 films. The structural and compositional analysis shows that the doping is in form of alkali metal‐sulfur chemical bond at both surface and grain boundaries of Sb2S3 films. Compared with the pristine Sb2S3, we observe that Li and Na doping are not able to improve the device efficiency, while K, Rb, and Cs notably increase energy conversion efficiency. The most effective enhancement is found in Cs‐doped Sb2S3, where the carrier concentration, crystallinity, and film formability show remarkable improvement. The device based on the Cs‐Sb2S3 film delivers a power conversion efficiency of 6.56%, which is the highest efficiency in planar heterojunction Sb2S3 solar cells, regardless of whether the films are fabricated by a solution process or thermal deposition. This research identifies that doping of heavy alkali metals is an effective approach to improve the performance of Sb2S3 solar cells.

Tailoring Crystal Structure of FA0.83Cs0.17PbI3 Perovskite Through Guanidinium Doping for Enhanced Performance and Tunable Hysteresis of Planar Perovskite Solar Cells

AbstractCurrent–voltage hysteresis of perovskite solar cells (PSCs) has raised the concern of accurate performance measurement in practice. Although various theories have been proposed to elucidate this phenomenon, the origin of hysteresis is still an open question. Herein, the use of guanidinium cation (Gu+)‐dopant is demonstrated to tailor the crystal structure of mixed‐cation formamidinium‐cesium lead triiodide (FA0.83Cs0.17PbI3) perovskite, resulting in an improved energy conversion efficiency and tunable current–voltage hysteresis characteristic in planar solar cells. Particularly, when the concentration of Gu‐dopant for the perovskite film increases, the normal hysteresis initially observed in the pristine PSC is first suppressed with 2%‐Gu‐dopant, then changed to inverted hysteresis with a higher Gu‐dopant. The hysteresis tunability behavior is attributed to the interplay of charge/ion accumulation and recombination at interfaces in the PSC. Furthermore, compared to the cell without Gu+‐dopant, the optimal content of 2% Gu+‐dopant also increases the device efficiency by 14%, reaching over 17% under one sun illumination.

Chemical sintering reduced grain boundary defects for stable planar perovskite solar cells

Organic–inorganic hybrid perovskite solar cells have attracted tremendous attention in photovoltaic research, but the presence of massive parasitic traps at the grain boundaries in perovskite films discourages efficient bimolecular recombination and carrier dynamics, which limits device performance and stability. Here we report a simple and fast chemical sintering protocol to substantially reduce grain boundary defects for as-formed films for different PbI2-templated perovskite materials. With this method parasitic traps on grain boundaries are intrinsically reduced, featuring the Urbach energy reduced by 1.5 meV. For optimal photovoltaic devices, we demonstrate a planar solar cell with power conversion efficiency (PCE) of 19.68% which retains 80% of this efficiency over 720 h in ambient air without any encapsulation. These findings offer a widely applicable, versatile process to efficiently reduce grain boundary defects and will be of interest to many other film material systems afflicted by polydispersity and grain boundary disturbances.

Propeller-Shaped, Triarylamine-Rich, and Dopant-Free Hole-Transporting Materials for Efficient n-i-p Perovskite Solar Cells.

By introducing six triarylamine groups to a hexaphenylbenzene (HPB) or a hexakis(2-thienyl)benzene (HTB) core, two propeller-shaped, triarylamine-rich, and low-cost hole-transporting materials (HTMs), which are termed as HPB-OMe and HTB-OMe, respectively, with considerable hole mobility, were obtained by easy synthetic routes. Solid-state planar perovskite CH3NH3PbI3 solar cells (PSCs) with two new HTMs showed high power conversion efficiencies (12.9% for HPB-OMe and 17.3% for HTB-OMe in forward scans) under standard 100 mW cm-2 AM 1.5G illumination without doping. A comparison of matched-degree of energy levels, hole-transporting ability, photovoltaic conversion efficiencies, and recombination of the two HTMs indicated that developing multi-triarylamine- and thiophene-rich molecules provides candidate and efficient dopant-free HTMs for PSCs.

Investigation on the Angle and Spectral Dependence of the Internal and the External Quantum Efficiency of Crystalline Silicon Solar Cells and Modules

To improve energy yield predictions and to fully understand the physical behavior of solar cells, it is necessary to investigate the effects caused by a change in the angle of incidence. All relevant angle-dependent effects are presented in this paper and angular correction factors are introduced. A new analytical model is presented, which includes internal reflection, free carrier absorption, and other parasitic absorption processes. The angular effects were exemplarily studied for the case of a very simple planar solar cell sample and a standard module sample. With an effective angle approach, the variation of the internal quantum efficiency in the standard solar module could be emulated and the results were verified with the help of a ray tracing tool developed for this purpose. The influence of the different angular factors on the current density of a standard module at an incidence angle of 70° is finally presented.

Nonequilibrium Theory of the Conversion Efficiency Limit of Solar Cells Including Thermalization and Extraction of Carriers

The ideal solar cell conversion efficiency limit known as the Shockley-Queisser (SQ) limit, which is based on a detailed balance between absorption and radiation, has long been a target for solar cell researchers. While the theory for this limit uses several assumptions, the requirements in real devices have not been discussed fully. Given the current situation in which research-level cell efficiencies are approaching the SQ limit, a quantitative argument with regard to these requirements is worthwhile in terms of understanding of the remaining loss mechanisms in current devices and the device characteristics of solar cells that are operating outside the detailed balance conditions. Here we examine two basic assumptions: (1) that the photo-generated carriers lose their kinetic energy via phonon emission in a moment (fast thermalization), and (2) that the photo-generated carriers are extracted into carrier reservoirs in a moment (fast extraction). Using a model that accounts for the carrier relaxation and extraction dynamics, we reformulate the nonequilibrium theory for solar cells in a manner that covers both the equilibrium and nonequilibrium regimes. Using a simple planar solar cell as an example, we address the parameter regime in terms of the carrier extraction time and then consider where the conventional SQ theory applies and what could happen outside the applicable range.

Polymeric rheology modifier allows single-step coating of perovskite ink for highly efficient and stable solar cells

Developing environmental friendly solution-processed hybrid perovskite films, with a compelling combination of reproducibility and moisture stability, is a highly desirable prospect to foster hybrid perovskite solar cells uptake in a fiercely competitive high-tech market. Herein, starch biopolymer is exploited as a rheological modifier to tailor the viscosity of perovskite precursor solutions, in order to allow the development of stable inks that can be straightforwardly deposited in a single coating step at mild-temperature, without the use of toxic solvents, to obtain uniform perovskite thin films. Importantly, the as conceived methylammonium lead iodide (MAPbI3) perovskite-starch composite film, integrated in a fully solution processed planar solar cell architecture, featured high power conversion efficiency of 17.2%, which is the highest reported for polymer-perovskite blends, improved moisture stability, more than 800 h stored in humid environment (50%), and resistance to bending stress in flexible devices. Moreover, it is worth to highlight how transmittance and thickness of the composite films can be simply adjusted by varying the perovskite inks viscosity with starch, envisioning the future implementation of such hybrid perovskite composites in printing technology and in different optoelectronic devices.

CNT fibres as dual counter-electrode/current-collector in highly efficient and stable dye-sensitized solar cells

This work demonstrates that carbon nanotube (CNT) fiber electrodes consisting of a mesoporous and crystalline network of few-layer CNTs can be used as free-standing, unipolar, and dual counter-electrode (CE)/current-collectors in highly efficient and stable planar dye-sensitized solar cells (DSSCs). After device optimization, particularly in terms of photoanode thickness, the solar energy conversion efficiency reached 8.8%, which is comparable to devices with platinum CE (8.7%). Through study of symmetric cells using electrochemical impedance spectroscopy (EIS) measurements, this work discloses the first clear identification of the different processes involved in the use of CNTf electrodes as CE, namely bulk ion diffusion, ion diffusion inside the mesoporous electrode, and charge transfer at the CNT surface. These results provide clear directors for a further understanding of the fundamental catalytic properties of CNTf fibers towards improving their photoelectrochemical features. Finally, we assemble new device architectures, namely i) a free-standing CNT-CEs (unipolar electrode) device with two photoanodes facing each other to circumvent the lack of transparency of CNTs without losing performance, and ii) large-area solar cells (>10 cm2) with 10 devices interconnected in parallel along 1 m continuous CNTf-CE, featuring efficiencies comparable to the-state-of-the-art carbon-based DSSC modules.

2D-Quasi-2D-3D Hierarchy Structure for Tin Perovskite Solar Cells with Enhanced Efficiency and Stability

The power conversion efficiency (PCE) of tin perovskite solar cells is impeded by the extremely poor resistance to oxidation and high density of intrinsic Sn vacancies. Herein, we grow a 2D-quasi-2D-3D Sn perovskite film using removable pseudohalogen NH4SCN as a structure regulator. This hierarchy structure remarkably enhances air stability resulting from the parallel growth of 2D PEA(2)SnI(4) as the surface layer. We then explore the hierarchy structure perovskite films in planar structural solar cells, which generate a PCE up to 9.41%. The device retains 90% of its initial performance for almost 600 hr. Our results suggest that adding removable NH4SCN in a perovskite precursor can significantly improve the stability and photovoltaic performance of Sn perovskite. This finding provides a powerful strategy to manipulate the structure of low-dimensional perovskite in order to enhance the performance of perovskite solar cells.

Improvement of organic solar cell performance via the incorporation of a MgO cathode interlayer fabricated by a reaction of thermally deposited Mg with MoO3

The use of magnesium oxide (MgO), which was formed by a reaction of thermally deposited magnesium with molybdenum trioxide, as a cathode interlayer material in vacuum-processed, planar pn-heterojunction organic solar cells (OSCs) using copper phthalocyanine and C70 and bulk-heterojunction (BHJ) OSCs using tris[(5-phenylthiophen-2-yl)phenyl]amine and C70 reduced the series resistance, thus improving the fill factor and power conversion efficiency (PCE). On the other hand, the use of the MgO cathode interlayer in solution-processed BHJ OSCs using poly(3-hexylthiophene) and [6,6]-phenyl-C71-butyric acid methyl ester improved the open-circuit voltage, thus improving the PCE. It is speculated that the improved performance is attributed to the high hole blocking ability of the MgO layer due to the deep-lying valence band level of MgO.

Fabrication of Sb₂S₃ Hybrid Solar Cells Based on Embedded Photoelectrodes of Ag Nanowires-Au Nanoparticles Composite.

The Ag nanowire (NW) + Au nanoparticle (NP)-embedded TiO2 photoelectrodes were adopted for conventional planar TiO2-based Sb2S3 hybrid solar cells to improve the cell efficiency. Compared to conventional planar TiO2-based Sb2S3 hybrid solar cells, the Ag NW + Au NP/TiO2-based Sb2S3 hybrid solar cells exhibited an improvement of approximately 40% in the cell efficiency due to the significant increase in both Jsc and Voc. These enhanced Jsc and Voc were attributed to the increased surface area, charge-collection efficiency, and light absorption by embedding the Ag NWs + Au NPs composite. The Ag NW + Au NP/TiO2-based Sb2S3 hybrid solar cells showed the highest efficiency of 2.17%, demonstrating that the Ag NW + Au NP-embedded TiO2 photoelectrode was a suitable photoelectrode structure to improve the power conversion efficiency in the Sb2S3 hybrid solar cells.

All‐Inorganic CsPb1−xGexI2Br Perovskite with Enhanced Phase Stability and Photovoltaic Performance

AbstractCompared with organic‐inorganic perovskites, all‐inorganic cesium‐based perovskites without volatile organic compounds have gained extensive interests because of the high thermal stability. However, they have a problem on phase transition from cubic phase (active for photo‐electric conversion) to orthorhombic phase (inactive for photo‐electric conversion) at room temperature, which has hindered further progress. Herein, novel inorganic CsPb1−xGexI2Br perovskites were prepared in humid ambient atmosphere without a glovebox. The phase stability of the all‐inorganic perovskite was effectively enhanced after germanium addition. In addition, the highest power conversion efficiency of 10.8 % with high open‐circuit voltage (VOC) of 1.27 V in a planar solar cell based on CsPb0.8Ge0.2I2Br perovskite was achieved. Furthermore, the highest VOC up to 1.34 V was obtained by CsPb0.7Ge0.3I2Br perovskite, which is a remarkable record in the field of all‐inorganic perovskite solar cells. More importantly, all the photovoltaic parameters of CsPb0.8Ge0.2I2Br perovskite solar cells showed nearly no decay after 7 h measurement in 50–60 % relative humidity without encapsulation.