We present a novel approach to simplify the rear-side a-Si:H patterning of silicon heterojunction interdigitated back-contact solar cells. In our current process, laser ablation and lift-off are used. Since lift-off is not industrially-viable, we propose to replace it with a selective deposition process which ensures a-Si:H is realised only on c-Si surface and not on the SiOx mask, at the end of the process, based on cycles of a-Si:H deposition and etching. While neither the deposition nor the etching is truly selective, this method relies on the difference of a-Si:H etch rates on c-Si and SiOx surfaces to achieve selectivity as the net end-result. The main challenge is addressing the trade-off between selectivity and c-Si surface passivation.
A GaN/Si nanoheterostructure array was synthesized using the functional substrate of silicon nanoporous pillar array (Si-NPA) by CVD method. An n-GaN nanocolumnar/p-Si nanocrystalline nanoheterojuction array solar cell was fabricated and the GaN nanocolumnar grew along the [0001] direction. The device has an average integrated reflection of ∼4.79% at the range of 300-1200 nm. The solar cell showed aVoc of 0.82 V, aJsc of 23.21 mA, aFF of 38.3% and a maximum power conversion efficiency of 7.29%. The results provide a new conception of mass-nanoheterojuctions for photovoltaic filed.
Passivated emitter rear contact (PERC) cells offer increased power conversion efficiency but also present several degradation risks compared to the traditional aluminum back surface field (Al-BSF) cell, including instability of the passivation layer and increased light-induced degradation. Newer generations of bifacial PERC cells with localized back contacts (as opposed to full rear side metalization) introduce further vulnerabilities such as mechanical cracking and greater susceptibility to corrosion. In this work, we evaluate these degradation modes through accelerated exposures of full-size modules, using advanced characterization and analysis techniques. Damp-heat and thermal cycling are used to activate distinct degradation modes in Al-BSF, PERC, and bifacial PERC full-size modules. At stepwise intervals during exposure, the modules are measured by $I -V$ curve tracing and electroluminescence (EL) imaging. EL images are standardized to allow for calculation of quantitative image parameters to be compared with standard $I -V$ parameters. Correlation of parameters extracted from $I -V$ and EL reveals statistical relationships between degradation mechanisms and performance, for module and accelerated exposure type. Bifacial PERC modules showed both the greatest power degradation in damp heat, and the most cell cracking in thermal cycling. The greater power degradation through damp heat exposure for modules with bifacial PERC cells is likely the result of both increased susceptibility of this cell type to corrosion, and instability of the rear-side encapsulant, white EVA.
The photovoltaic industry is driven by manufacturing cost and is continuously working on optimizing its production output. As production sites are increasing significantly in size, large data sets are generated that require adequate processing for line optimization. As in other industries machine learning is one way to address this task. In this study a machine learning algorithm is used for trouble shooting of production data to identify parameters which are responsible to high variances in energy conversion efficiency.
Unmanned Aerial Vehicles (UAVs) are expanding in both military and commercial markets. Most UAVs are limited in flight duration and due in part to the weight of energy storage. Solar cells integrated into the wing surface can provide additional power dependent on the sun, weight, wing area, and efficiency. NRL has built a variety of wings for UAVs from solar cell technologies which include Si, thin flexible GaAs, triple junction InGaP/GaAs/Ge, and Inverted Metamorphic Multi-Junction (IMM) for comparison. NRL has flown these solar technologies demonstrating flights in excess of 10 hrs with only 4 hrs of onboard energy storage. This paper intends to provide a side-by-side comparison of these technologies for design and cost considerations on mission feasibility.
The article presents operation principle, measurement results and perspectives connected with the implementation of textured structure, acting as a selectively transparent layer on the top surface of the flexible, thin-film solar cell optical converter. The analyzed structure is designed for the application in the down-shifting polymer conversion setup, designed for insulation spectrum adjustment.
A key strategy for further reducing the cost of solar electricity is through the development of very-high efficiency silicon solar cells (> 27%). The challenge in achieving this goal lies in overcoming limitations imposed by the electronic quality of the silicon wafers themselves. To overcome this challenge, there is an urgent need for a refined understanding of defects limiting the electronic quality of silicon wafers. This paper provides a nuanced and detailed picture what constitutes accurate recombination parameters for defects in silicon. It outlines three widespread issues in existing measurements of recombination parameters. It enables robust simulation of the lifetime in silicon for solar cell applications.
Back end interconnection technology is presented for CIGS using laser scribing and inkjet printing of dielectric material. Shunt-free laser scribing of CIGS is shown, which is essential in the back end approach for monolithic serial interconnection. Full back end interconnected mini-modules of 20x20cm2 were made and show no electrical losses compared to the reference cells. These results show the feasibility of complete module manufacturing after full area deposition of the CIGS stack, enabling cheaper and more flexible production of PV modules.
Intrinsic structural anisotropy in methylammonium (MA) and formamidinium (FA) lead halide perovskites were examined and by various laboratory X-ray diffraction techniques including both out-of-plane and in-plane geometries. Our quantitative analysis revealed the presence of anisotropic strain in the cubic perovskites. Comparative studies on FAPbBr 3 and MAPbBr 3 showed that the FAPbBr 3 lattice was more strained and the anisotropic features were rationalized using ab initio molecular dynamics simulations (AIMD). Our results shed light on future perovskite film design to minimize strain induced decomposition.
We present a modelling study of thin silicon-based solar cells endowed with periodic and decoupled front/back textures. After careful optimization, the proposed device models exhibit absorption beyond the Lambertian light trapping limit for a wide range of light angles of incidence. The advanced light management scheme is applied to (nano)crystalline silicon solar cells, where the benefits of texturing the absorber rather than the supporting layers is clear, and to barium (di)silicide solar cells, which could achieve an implied photocurrent density of 41.1 mA/cm2 for a thickness of only 2 μm.
An advanced version of the XTJ family of space solar cells called XTJ Targeted Environment (XTE) is being developed at Spectrolab. The XTE cell consists of four specifically designed product variants: standard radiation fluence (SF) for GEO missions, low radiation fluence (LF) for LEO missions, high radiation fluence (HF) for orbit transfer or MEO missions, and LILT for low intensity, low temperature outer planetary environments. The XTE SF and XTE LF variants have demonstrated an average AM0 efficiencies of 32.2% and 32.6% in multiple engineering confidence cell builds. The XTE LILT cells have also achieved an average BOL efficiency of 36.6% under AM0 5.5 AU, -140°C, 4.5 mW/cm 2 Jupiter conditions in an engineering confidence cell build. Three (SF, LF, and LILT) of the four XTE cell variants completed engineering confidence tests and are underway to complete AIAA-S-111 qualification.
Photovoltaic systems (PV) are rapidly introduced in Japan. Since their output changes depending on weather conditions, supply and demand control of the electric power system is becoming difficult. Based on this background, we developed a prediction system of PV output to help the controlling and planning in electric power company (Table 1) [1]. This system has the feature of the hybrid system, because it predicts a PV output by combining numerical weather forecast and satellite cloud images. Our system was put into practical use for the first time in a Japanese major electric power companies [2]. We introduce a detail of prediction method and prediction accuracy in this paper.
Dip coating is a highly efficient solution deposition technique suitable for chemically-synthesized perovskite quantum dots (PQDs). In dip coating, withdrawal speed is a key factor that determines thickness of the films and may affect their quality. In this work, the optimum withdrawal speed that would result to optically smooth cesium lead halide (CsPbX3) PQD films on GaAs substrates was investigated through atomic force microscopy and optical characterization. Results revealed that the optimum withdrawal speed for producing high quality PQD film on GaAs is 10 mm/s. This work may contribute to the use of dip coating for low-cost, large-scale PQD deposition.
We present four-terminal perovskite-Si and perovskite-CIGS tandem solar modules that are fully scalable to commercial dimensions. Starting from small cells of 0.13 cm(2), we scale up the tandem devices by a factor of 30 to modules of 4 cm2. By using a low-loss module design and optimized light coupling, we demonstrate perovskite-Si and perovskite-CIGS tandem solar modules which outperform the stand-alone devices on the large area, representing a key milestone for perovskite-based tandem photovoltaics. Moreover, the tandem solar module architecture is compatible with industrially scalable fabrication techniques, thus opening the route towards production of high-performance large-area perovskite-based tandem solar modules.
Access to lattice matched narrow bandgap semiconductors is a challenge for improved efficiency of GaAs based multi-junction solar cells (MJSCs). GaSb has a bandgap of 0.72 eV and is ideally suited to be used as a Near-Infrared subcell for MJSCs. However, when used as a replacement for Germanium in GaAs based MJSCs, the large lattice mismatch between GaSb and GaAs results in significant threading dislocation density in the GaSb subcell. The threading dislocation density in the GaSb epilayer can be reduced to a certain extent by the realization of 90° interfacial misfit dislocation arrays (IMF) between the GaSb and GaAs layers. The substrate temperature during the growth of the GaSb epi-layer on GaAs has a strong impact on the threading dislocation density while making use of the IMF technique. In this study, several substrate temperatures (ranging from 350°C to 540°C) are explored to achieve reduced threading dislocation density which is measured using both plan-view Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD) rocking curve analysis. A low growth temperature (of 420°C) shows the reduction of threading dislocation to the level of ~1.3×10 8 cm -2 .
Organic-inorganic perovskite solar cells have achieved power conversion efficiencies that rival the established mainstream photovoltaic technologies, however, the lack of longterm stability presents one major hurdle for their commercialization. Here, we investigate the impact of low-cost epoxy encapsulation on device stability of large-area, laser-patterned perovskite solar cells and mini-modules, yielding results relevant to large modules for commercial applications. We track the performance evolution of our devices stored under different conditions. On this basis, we employ light-beam induced current (LBIC) to spatially resolve the photocurrent degradation of these devices, showing the striking contrast between devices with and without encapsulation after three months (~ 2000 hours) of storage under ambient and humid conditions.
The proper design of the multi-junction solar cell (MJSC) requires the optimisation search through the vast parameter space, with parameters for the proper operation quite often being constrained, like the current matching throughout the cell. Due to high complexity number of MJSC device parameters might be huge, which makes it a demanding task for the most of the optimising strategies based on gradient algorithm. One way to overcome those difficulties is to employ the global optimisation algorithms based on the stochastic search. We present the procedure for the design of MJSC based on the heuristic method, the genetic algorithm, taking into account physical parameters of the solar cell as well as various relevant radiative and non-radiative losses. In the presented model, the number of optimising parameters is 5M+1 for a series constrained M-junctions solar cell. Diffusion dark current, radiative and Auger recombinations are taken into account with actual ASTM G173-03 Global tilted solar spectra, while the absorption properties of individual SCs were calculated using the multi band k·p Hamiltonian. We predicted the efficiencies in case of M=4 to be 50.8% and 55.2% when all losses are taken into account and with only radiative recombination, respectively.
Concentrating photovoltaics (CPV) can increase the efficiency and reduce the cost of photovoltaic power in space. We introduce a new monolithic, ultrathin, and lightweight CPV paradigm based on a transfer-printed microscale solar cell array. In our reflective design, the microcell array is embedded in a radiation-tolerant glass optic that delivers 83% optical efficiency with a ±7° acceptance angle at 32× geometric gain. The system is <;1 mm thick and capable of achieving a specific power density of 352 W/kg using state-of-the-art triple junction microcells.
Recently, we have proposed a new type solar cells utilizing photon up-conversion phenomenon, called two-step photon up-conversion solar cells for realizing high conversion efficiency solar cells. Here, achieving efficient intraband photo excitation is indispensable. This solar cell has a simple single junction structure containing a hetero-interface. In this study, we investigated the applying electric field dependence of two-step photon up-conversion occurring at the hetero-interface. We found that dense electron accumulation and an appropriate electric field enable to dramatically increase the intraband excitation strength and the carrier collection efficiency at the hetero-interface.
In this paper, we explore a rotating shadow band (RSB) configuration for the EKO MS-711 spectroradiometer to measure the global, diffuse and direct components of spectral irradiance. An RSB configuration allows lowering the costs associated with the instrumentation and maintenance required to measure the components of spectral irradiance. Since only one spectroradiometer is used for the measurement of the spectral irradiance components, discrepancies associated to sensor calibration can be minimized. This work presents a study to validate the EKO RSB spectroradiometer accuracy in measuring the direct normal irradiance (DNI). A comparison is made between the measurements performed with the RSB spectroradiometer and a collimated spectroradiometer in Mauna Loa Observatory. The results of the comparison show an agreement within 2% to 5% between the DNI estimated by the RSB and collimation configurations for solar zenith angles smaller than 70 degrees. Larger deviations approximated to 10% are found for larger angles of incidence.
