Ultra-thin Absorber Layer Research Articles

Enhancing light absorption in ultra-thin perovskite solar cells using plasmonic gold nanoparticle clusters

Perovskite solar cells with ultra-thin absorber layers offer potential cost savings in manufacturing, but their reduced thickness can limit light absorption and efficiency. This work explores using plasmonic gold nanoparticles as a light-trapping strategy to compensate for lower absorption in ultra-thin perovskite devices. Numerical simulations investigate embedding 25 nm radius gold nanoparticles within the 200 nm thick perovskite active layer to boost optical absorption through near-field enhancement and light scattering effects. The solar cell structure incorporating these plasmonic nanoparticles achieves a substantially higher short-circuit current density of 23.10 mA cm−2 compared to 18.70 mA cm−2 for a reference cell without nanoparticles. This study provides design approaches for realizing high-efficiency yet cost-effective ultra-thin perovskite photovoltaics by harnessing plasmonic light-trapping techniques. The results display methodologies to improve photon absorption and power conversion in thin-film perovskite devices through strategic nanoparticle integration.

Dithiocarbamate‐Based Solution Processing for Cation Disorder Engineering in AgBiS2 Solar Absorber Thin Films

AbstractCation disorders refer to the phenomenon where cations are randomly distributed in multi‐cation systems. These disorders have emerged as an effective strategy for tailoring material properties across diverse applications. Notably, engineering cation disorder in AgBiS2 has garnered attention, owing to its remarkable enhancement of light absorption coefficients, which are crucial for efficient solar energy conversion in ultrathin light absorber layers. In this study, a novel dithiocarbamate (DTC)‐based solution processing method designed to control cation disorder is presented in AgBiS2 thin films. Unlike conventional approaches that rely on heat treatment, the strategy is based on molecular coordination dynamics between DTC and metal cations. By adjusting the ratio of DTC to the metal cations, the formation of cation‐disordered AgBiS2 thin films is demonstrated. Notably, the order‐to‐disorder transition is solely dependent on the DTC‐metal coordination and independent of the annealing temperature. These disordered films exhibit a high light absorption coefficient (>5 × 105 cm−1), mirroring the characteristics of thermally‐treated cation‐disordered AgBiS2 nanocrystals reported previously. The disordered AgBiS2 thin‐film photodetector exhibited a higher photocurrent density and responsivity compared to its ordered counterpart. The approach establishes a novel platform for cation disorder engineering, paving the way for advancements in cation‐disordered materials with diverse applications.

Short-Wave Infrared Colloidal QD Photodetector with Nanosecond Response Times Enabled by Ultrathin Absorber Layers.

Ultrafast short-wavelength infrared (SWIR) photodetection is of great interest for emerging automated vision and spatial mapping technologies. Colloidal quantum dots (QDs) stand out for SWIR photodetection compared to epitaxial (In,Ga)As or (Hg,Cd)Te semiconductors by their combining a size-tunable bandgap and a suitability for cost-effective, solution-based processing. However, achieving ultrafast, nanosecond-level response time has remained an outstanding challenge for QD-based SWIR photodiodes (QDPDs). Here, record 4ns response time in PbS-based QDPDs that operate at SWIR wavelengths is reported, a result reaching the requirement of SWIR light detection and ranging based on colloidal QDs. These ultrafast QDPDs combine a thin active layer to reduce the carrier transport time and a small area to inhibit slow capacitive discharging. By implementing a concentration gradient ligand exchange method, high-quality p-n junctions are fabricated in these ultrathin QDPDs. Moreover, these ultrathin QDPDs attain an external quantum efficiency of 42% at 1330nm, due to a 2.5-fold enhanced light absorption through the formation of a Fabry-Perot cavity within the QDPD and the highly efficient extraction (98%) of photogenerated charge carriers. Based on these results, it is estimated that a further increase of the charge-carrier mobility can lead to PbS QDPDs with sub-nanosecond response time.

All-Inorganic Hydrothermally Processed Semitransparent Sb2S3 Solar Cells with CuSCN as the Hole Transport Layer.

An inorganic wide-bandgap hole transport layer (HTL), copper(I) thiocyanate (CuSCN), is employed in inorganic planar hydrothermally deposited Sb2S3 solar cells. With excellent hole transport properties and uniform compact morphology, the solution-processed CuSCN layer suppresses the leakage current and improves charge selectivity in an n-i-p-type solar cell structure. The device without the HTL (FTO/CdS/Sb2S3/Au) delivers a modest power conversion efficiency (PCE) of 1.54%, which increases to 2.46% with the introduction of CuSCN (FTO/CdS/Sb2S3/CuSCN/Au). This PCE is a significant improvement compared with the previous reports of planar Sb2S3 solar cells employing CuSCN. CuSCN is therefore a promising alternative to expensive and inherently unstable organic HTLs. In addition, CuSCN makes an excellent optically transparent (with average transmittance >90% in the visible region) and shunt-blocking HTL layer in pinhole-prone ultrathin (<100 nm) semitransparent absorber layers grown by green and facile hydrothermal deposition. A semitransparent device is fabricated using an ultrathin Au layer (∼10 nm) with a PCE of 2.13% and an average visible transmittance of 13.7%.

Theoretical study of Ag and Au triple core-shell spherical plasmonic nanoparticles in ultra-thin film perovskite solar cells.

This work demonstrates the enhancement of the power conversion efficiency of thin film organic-inorganic halide perovskites solar cells by embedding triple-core-shell spherical plasmonic nanoparticles into the absorber layer. A dielectric-metal-dielectric nanoparticle can be substituted for embedded metallic nanoparticles in the absorbing layer to modify their chemical and thermal stability. By solving Maxwell's equations with the three-dimensional finite difference time domain method, the proposed high-efficiency perovskite solar cell has been optically simulated. Additionally, the electrical parameters have been determined through numerical simulations of coupled Poisson and continuity equations. Based on electro-optical simulation results, the short-circuit current density of the proposed perovskite solar cell with triple core-shell nanoparticles consisting of dielectric-gold-dielectric and dielectric-silver-dielectric nanoparticles has been enhanced by approximately 25% and 29%, respectively, as compared to a perovskite solar cell without nanoparticles. By contrast, for pure gold and silver nanoparticles, the generated short-circuit current density increased by nearly 9% and 12%, respectively. Furthermore, in the optimal case of the perovskite solar cell the open-circuit voltage, the short-circuit current density, the fill factor, and the power conversion efficiency have been achieved at 1.06 V, 25 mAcm-2, 0.872, and 23.00%, respectively. Last but not least, lead toxicity has been reduced due to the ultra-thin perovskite absorber layer, and this study provides a detailed roadmap for the use of low-cost triple core-shell nanoparticles for efficient ultra-thin-film perovskite solar cells.

All-epitaxial resonant cavity enhanced long-wave infrared detectors for focal plane arrays

We demonstrate a monolithic all-epitaxial resonant-cavity architecture for long-wave infrared photodetectors with substrate-side illumination. An nBn detector with an ultra-thin (t≈350 nm) absorber layer is integrated into a leaky resonant cavity, formed using semi-transparent highly doped (n++) epitaxial layers, and aligned to the anti-node of the cavity's standing wave. The devices are characterized electrically and optically and demonstrate an external quantum efficiency of ∼25% at T=180 K in an architecture compatible with focal plane array configurations.

Seed Layer Optimisation for Ultra-Thin Sb2Se3 Solar Cells on TiO2 by Vapour Transport Deposition.

Antimony selenide (Sb2Se3) material has drawn considerable attention as an Earth-abundant and non-toxic photovoltaic absorber. The power conversion efficiency of Sb2Se3-based solar cells increased from less than 2% to over 10% in a decade. Different deposition methods were implemented to synthesize Sb2Se3 thin films, and various device structures were tested. In search of a more environmentally friendly device composition, the common CdS buffer layer is being replaced with oxides. It was identified that on oxide substrates such as TiO2 using vacuum-based close-space deposition methods, an intermediate deposition step was required to produce high-quality thin films. However, little or no investigation was carried out using another very successful vacuum deposition approach in Sb2Se3 technology called vapour transport deposition (VTD). In this work, we present optimized VTD process conditions to achieve compact, pinhole-free, ultra-thin (<400 nm) Sb2Se3 absorber layers. Three process steps were designed to first deposit the seed layer, then anneal it and, at the final stage, deposit a complete Sb2Se3 absorber. Fabricated solar cells using absorbers as thin as 400 nm generated a short-circuit current density over 30 mA/cm2, which demonstrates both the very high absorption capabilities of Sb2Se3 material and the prospects for ultra-thin solar cell application.

SIMULATION AND IMPROVEMENT OF THE PERFORMANCE OF CdTe SOLAR CELL WITH ULTRATHIN ABSORBER LAYER

In the few past years, the usage of CdTe thin-film solar cells has increased considerably due to their high efficiency, performance stability and cost effectiveness. In this work, a conventional structure of FTO–[Formula: see text]-SnO2–CdS–CdTe was simulated initially to verify the simulation process. An ultrathin absorber layer was considered to make the device more economical. A [Formula: see text]-type copper oxide thin film was employed at the back contact as a hole transport–electron blocking layer (HT–EBL). Besides, the use of a bilayer ZnS–CdS compound and a monolayer CdS:Zn compound as the electron transport layer was also studied. The proposed modeled cell parameters then were optimized to increase the efficiency.

An Ultra-Thin Near-Perfect Absorber via Block Copolymer Engineered Metasurfaces

Producing ultrathin light absorber layers is attractive towards the integration of lightweight planar components in electronic, photonic, and sensor devices. In this work, we report the experimental demonstration of a thin gold (Au) metallic metasurface with near-perfect visible absorption (∼95 %). Au nanoresonators possessing heights from 5 − 15 nm with sub-50 nm diameters were engineered by block copolymer (BCP) templating. The Au nanoresonators were fabricated on an alumina (Al2O3) spacer layer and a reflecting Au mirror, in a film-coupled nanoparticle design. The BCP nanopatterning strategy to produce desired heights of Au nanoresonators was tailored to achieve near-perfect absorption at ≈ 600 nm. The experimental insight described in this work is a step forward towards realizing large area flat optics applications derived from subwavelength-thin metasurfaces.

Comparison of Mo and ITO back contacts in CIGSe solar cells: Vanishing of the main capacitance step

AbstractAdmittance measurements of Cu (In, Ga)Se2 (CIGSe) solar cells typically show at least one capacitance step, the so‐called N1 signal. Its origin is still under debate, even though the signal is present in almost all CIGSe solar cells. In this work, CIGSe solar cells with different absorber layer thicknesses have been prepared on Mo and on indium tin oxide (ITO)‐based back contacts. The samples were analyzed by temperature‐dependent current–voltage (JV) and admittance measurements. No N1 signal was found for ITO‐based samples. The N1 signal was also absent in Mo‐based solar cells with an ultrathin absorber layer, unless a forward bias voltage was applied. The observations can be consistently explained by a back contact barrier, which is only present in the Mo‐based solar cells. The explanation is further supported by measured JV curves and by theoretical simulations. The results give a strong indication that the N1‐signal is due to a back contact barrier. While a back contact barrier is not necessarily detrimental for regular CIGSe solar cells, it may be an issue for CIGSe solar cells with ultrathin absorbers, where a so‐called punch‐through effect can occur.

High-performance ultrathin Cu(In,Ga)Se2 solar cell optimized by silvaco tools

In this work, we investigated the influence of the cell pitch, opening width, Ga/(In + Ga) ratio, absorber layer thickness, and doping on ultrathin CIGS solar cell performance by using ATLAS tools. First, to validate our investigated solar cell, we discuss and compare our simulation models with fabricated cells with/without rear-passivation Al2O3/Cu(In1−xGax)Se2. We observed significant improvements in cell performance while using a thin film Al2O3 for the rear-passivation with a high density of negative charge, where the rear side contact recombination losses can then be reduced. The simulation results follow the experimental trends, highlighting the beneficial effects of rear-passivation in the ultrathin absorber layer. However, poor passivation was observed when a rear-passivation layer is with a high density of positive charge or in high contact resistance at Ag/CIGS interface. Consequently, the optimum combination led to achieving 14.30% with 1016 cm−3, 2.5 µm, and 250 nm for absorber doping, cell pitch, and cell width, respectively. The obtained results from the simulated cells were compared to the recently published research work.

Ultrathin Solar Cells Based on Atomic Layer Deposition of Cubic versus Orthorhombic Tin Monosulfide

Tin monosulfide can be grown in cubic (π-SnS) and orthorhombic (α-SnS) polymorphs by low-temperature atomic layer deposition (ALD). The optical properties of these polymorphs make them attractive for the realization of plasmonic solar cells with ultrathin absorber layers down to 10 nm in thickness. SnS is also an earth-abundant and nontoxic compound semiconductor of high interest for regular thin-film photovoltaics. To better understand the behavior of the two SnS polymorphs in ultrathin solar cell configurations, we here fabricate, characterize, and analyze a range of such devices. ALD is used to grow SnS and form heterojunctions with zinc oxysulfide [Zn(O,S)], acting as a buffer layer with a composition-tunable bandgap. Apart from the roles of the SnS polymorph and Zn(O,S) composition, the effects of the back contact material and thicknesses of buffer and absorber layers are investigated. Devices using π-SnS and pure ZnO buffers yield the highest photocurrents (3.1 mA/cm2) and higher open circuit voltage (159 mV) than similar α-SnS-based devices. Analysis of the equivalent-circuit parameters suggests that interface recombination limits the voltage for these devices. While Zn(O,S) with a higher sulfur content provides chemical passivation of the SnS interface and excessive open circuit voltages above 600 mV, it also exhibits a too high conduction band offset, which hampers current collection. A growth delay during the ALD of Zn(O,S) on SnS initially amplifies the known sulfur–oxygen exchange reaction, such that a sulfur-rich Zn(O,S) region forms next to the SnS interface. This causes a thin ZnS-like barrier to form already for low cycle fractions of the H2S precursor in the ALD super-cycle. Voltage and fill factor trends suggest an optimal SnS absorber layer thickness in the range of 15–35 nm, presenting an opportunity for plasmonic absorption enhancement. Devices with π-SnS show most promise, but interface recombination versus current-blocking is a dilemma for the SnS/Zn(O,S) heterojunction.

Numerical simulation of a new device architecture for CIGS-based thin-film solar cells using 1D-SCAPS simulator

In this study, we report on a low-cost, highly efficient, and Cd-free Cu (In and Ga) Se2 (CIGS)-based solar cell for an alternative to conventional CIGS-based solar cells. To maintain the proposed model as close as possible to the real behavior of thin-film solar cells, we produced a device with a p-Si/p-CIGS/In2S3/i-ZnO/Al-ZnO structure. The main objective of this study was to reduce the fabrication cost using an ultra-thin CIGS absorber layer with In2S3 buffer layer and obtain high performance. The solar cell performance of this proposed device was investigated using a 1D-solar cell capacitance simulator (SCAPS). The simulation was conducted in three stages. First, the cell was optimized by varying the thicknesses of the CIGS absorber and In2S3 buffer layer. The optimized structure was simulated at different operating temperatures. In each case, Voc, Jsc, FF, and the efficiency were calculated.The proposed device had a marked efficiency of ∼26 % with a 0.3 μm thick CIGS absorber layer. Varying the thickness of the In2S3 buffer layer had little effect, and as the temperature increased, the cell’s performance showed a downward trend.

Interface engineering of ultrathin Cu(In,Ga)Se2 solar cells on reflective back contacts

AbstractCu(In,Ga)Se2‐based (CIGS) solar cells with ultrathin (≤500 nm) absorber layers suffer from the low reflectivity of conventional Mo back contacts. Here, we design and investigate ohmic and reflective back contacts (RBC) made of multilayer stacks that are compatible with the direct deposition of CIGS at 500°C and above. Diffusion mechanisms and reactions at each interface and in the CIGS layer are carefully analyzed by energy dispersive X‐ray (EDX)/scanning transmission electron microscopy (STEM). It shows that the highly reflective silver mirror is efficiently encapsulated in ZnO:Al layers. The detrimental reaction between CIGS and the top In2O3:Sn (ITO) layer used for ohmic contact can be mitigated by adding a 3 nm thick Al2O3 layer and by decreasing the CIGS coevaporation temperature from 550°C to 500°C. It also improves the compositional grading of Ga toward the CIGS back interface, leading to increased open‐ circuit voltage and fill factor. The best ultrathin CIGS solar cell on RBC exhibits an efficiency of 13.5% (+1.0% as compared to our Mo reference) with a short‐circuit current density of 28.9 mA/cm2 (+2.6 mA/cm2) enabled by double‐pass absorption in the 510 nm thick CIGS absorber. RBC are easy to fabricate and could benefit other photovoltaic devices that require highly reflective and conductive contacts subject to high temperature processes.

Identification of surface and volume hot-carrier thermalization mechanisms in ultrathin GaAs layers

Hot-carrier solar cells offer the opportunity to harvest more energy than the limit set by the Shockley–Queisser model by reducing the losses due to the thermalization of photo-generated carriers. Previous reports have shown lower thermalization rates in thinner absorbers, but the origin of this phenomenon is not precisely understood. In this work, we investigate a series of ultrathin GaAs absorber layers sandwiched between AlGaAs barriers and transferred on host substrates with a gold back mirror. We perform power-dependent photoluminescence characterizations at different laser wavelengths from which we determine the carrier temperature in four absorber thicknesses between 20 and 200 nm. We observe a linear relationship between the absorbed power and the carrier temperature increase. By relating the absorbed and thermalized power, we extract a thermalization coefficient for all samples. It shows an affine dependence with the thickness, leading to the identification of distinct volume and surface contributions to thermalization. We confirm that volume thermalization is linked to LO phonon decay. We discuss the origin of the interface-related thermalization, showing that the effect of LO phonon transport is negligible. Overall, this work sheds new light on thermalization processes in ultrathin semiconductor layers and introduces a method to compare the performance of hot-carrier absorbers.

Progress and prospects for ultrathin solar cells

Ultrathin solar cells with thicknesses at least 10 times lower than conventional solar cells could have the unique potential to efficiently convert solar energy into electricity while enabling material savings, shorter deposition times and improved carrier collection in defective absorber materials. Efficient light absorption and hence high power conversion efficiency could be retained in ultrathin absorbers using light-trapping structures that enhance the optical path. Nevertheless, several technical challenges prevent the realization of a practical device. Here we review the state-of-the-art of c-Si, GaAs and Cu(In,Ga)(S,Se)2 ultrathin solar cells and compare their optical performances against theoretical light-trapping models. We then address challenges in the fabrication of ultrathin absorber layers and in nanoscale patterning of light-trapping structures and discuss strategies to ensure efficient charge collection. Finally, we propose practical architectures for ultrathin solar cells that combine photonic and electrical constraints, and identify future research directions and potential applications of ultrathin photovoltaic technologies. Ultrathin solar cells attract interest for their relatively low cost and potential novel applications. Here, Massiot et al. discuss their performance and the challenges in the fabrication of ultrathin absorbers, patterning of light trapping structures and ensuring efficient charge-carrier collection.

Single junction-based thin-film CIGS solar cells optimization with efficiencies approaching 24.5 %

This research paper proposes a numerical analysis of a new Cu(In1-xGax)Se2 (CIGS) based solar cell integrating an ultrathin absorber layer. The CIGS model is performed from the theoretical and experimental investigations taking into account the physical properties, dimensions, and thicknesses of the different layers by using Atlas SILVACO-TCAD tools. To improve the overall efficiency, magnesium fluoride (MgF2) thin film is used as the antireflective coating to maximize the photocurrent from the incident light intensity. The influence of the minority carrier lifetime, density of state, and interface defect density in the CIGS on the PV performance are investigated under the AM1.5 spectrum, 300 K. The novelty of the proposed solar cell consists of a CuInSe working as a back-surface field layer (BSF). The simulation results point out that the CuInSe BSF layer has a strong effect on cell performance. The use of ultrathin absorber layers (≤1 μm) can provide a new solution for recent advanced research on this topic. The investigation illustrates potential results for conversion efficiency improvement up to 24.5 % (Voc =751 mV, Jsc =41.44 mA/cm2, FF = 78.63 %).

Switchable Photocurrent Generation in an Ultrathin Resonant Cavity Solar Cell

Fabry-Perot-type resonant nanocavities allow for broadband enhancement of light absorption in ultrathin absorber layers. By introducing a switchable mirror, these thin film structures can be used a...

Ultrathin Nano-Absorbers in Photovoltaics: Prospects and Innovative Applications

Approaching the first terawatt of installations, photovoltaics (PV) are about to become the major source of electric power until the mid-century. The technology has proven to be long lasting and very versatile and today PV modules can be found in numerous applications. This is a great success of the entire community, but taking future growth for granted might be dangerous. Scientists have recently started to call for accelerated innovation and cost reduction. Here, we show how ultrathin absorber layers, only a few nanometers in thickness, together with strong light confinement can be used to address new applications for photovoltaics. We review the basics of this new type of solar cell and point out the requirements to the absorber layer material by optical simulation. Furthermore, we discuss innovative applications, which make use of the unique optical properties of the nano absorber solar cell architecture, such as spectrally selective PV and switchable photovoltaic windows.

Ultrathin microcrystalline hydrogenated Si/Ge alloyed tandem solar cells towards full solar spectrum conversion

Thin film solar cells have been proved the next generation photovoltaic devices due to their low cost, less material consumption and easy mass production. Among them, micro-crystalline Si and Ge based thin film solar cells have advantages of high efficiency and ultrathin absorber layers. Yet individual junction devices are limited in photoelectric conversion efficiency because of the restricted solar spectrum range for its specific absorber. In this work, we designed and simulated a multi-junction solar cell with its four sub-cells selectively absorbing the full solar spectrum including the ultraviolet, green, red as well as near infrared range, respectively. By tuning the Ge content, the record efficiency of 24.80% has been realized with the typical quadruple junction structure of a-Si:H/a-Si0.9Ge0.1:H/μc-Si:H/μc-Si0.5Ge0.5:H. To further reduce the material cost, thickness dependent device performances have been conducted. It can be found that the design of total thickness of 4 mm is the optimal device design in balancing the thickness and the PCE. While the design of ultrathin quadruple junction device with total thickness of 2 mm is the optimized device design regarding cost and long-term stability with a little bit more reduction in PCE. These results indicated that our solar cells combine the advantages of low cost and high stability. Our work may provide a general guidance rule of utilizing the full solar spectrum for developing high efficiency and ultrathin multi-junction solar cells.