Showing papers by "Miro Zeman published in 2022"
TL;DR: In this paper , the authors presented three types of In2O3-based TCOs, tin, fluorine, and tungsten-doped In 2O3 (ITO, IFO, and IWO), whose thickness has been optimally minimized.
Abstract: Reducing indium consumption, which is related to the transparent conductive oxide (TCO) use, is a key challenge for scaling up silicon heterojunction (SHJ) solar cell technology to terawatt level. In this work, we developed bifacial SHJ solar cells with reduced TCO thickness. We present three types of In2O3‐based TCOs, tin‐, fluorine‐, and tungsten‐doped In2O3 (ITO, IFO, and IWO), whose thickness has been optimally minimized. These are promising TCOs, respectively, from post‐transition metal doping, anionic doping, and transition metal doping and exhibit different opto‐electrical properties. We performed optical simulations and electrical investigations with varied TCO thicknesses. The results indicate that (i) reducing TCO thickness could yield larger current in both monofacial and bifacial SHJ devices; (ii) our IWO and IFO are favorable for n‐contact and p‐contact, respectively; and (iii) our ITO could serve well for both n‐contact and p‐contact. Interestingly, for the p‐contact, with the ITO thickness reducing from 75 nm to 25 nm, the average contact resistivity values show a decreasing trend from 390 mΩ cm2 to 114 mΩ cm2. With applying 25‐nm‐thick front IWO in n‐contact, and 25‐nm‐thick rear ITO use in p‐contact, we obtained front side efficiencies above 22% in bifacial SHJ solar cells. This represents a 67% TCO reduction with respect to a reference bifacial solar cell with 75‐nm‐thick TCO on both sides.
10 citations
TL;DR: In this paper , a dipole at the interface between the molybdenum oxide and the hydrogenated intrinsic amorphous silicon passivation layer is demonstrated, and the authors apply this knowledge to experimentally tailor the oxygen content in MoOx by plasma treatments (PTs).
Abstract: Thin films of transition metal oxides such as molybdenum oxide (MoOx) are attractive for application in silicon heterojunction solar cells for their potential to yield large short-circuit current density. However, full control of electrical properties of thin MoOx layers must be mastered to obtain an efficient hole collector. Here, we show that the key to control the MoOx layer quality is the interface between the MoOx and the hydrogenated intrinsic amorphous silicon passivation layer underneath. By means of ab initio modelling, we demonstrate a dipole at such interface and study its minimization in terms of work function variation to enable high performance hole transport. We apply this knowledge to experimentally tailor the oxygen content in MoOx by plasma treatments (PTs). PTs act as a barrier to oxygen diffusion/reaction and result in optimal electrical properties of the MoOx hole collector. With this approach, we can thin down the MoOx thickness to 1.7 nm and demonstrate short-circuit current density well above 40 mA/cm2 and a champion device exhibiting 23.83% conversion efficiency.
9 citations
TL;DR: In this paper , a new type of hybrid-shaped Cu finger is electromagnetically fabricated in a BF plating process, which is composed of a rectangular bottom part and a round top part, such that an utmost effective AR value of 1.73 is reached.
Abstract: Bifacial (BF) copper‐plated crystalline silicon solar cell is an attractive topic to concurrently reduce silver consumption and maintain good device performance. However, it is still challenging to realize a high aspect ratio (AR) of the metal fingers. Herein, a new type of hybrid‐shaped Cu finger is electromagnetically fabricated in a BF plating process. Cyclic voltammetry is employed to disclose the electrochemical behaviors of cupric ions in monofacial and simultaneous BF Cu‐plating processes, such that the controllability of the plating process could be assessed. The optimal hybrid Cu finger is composed of a rectangular bottom part and a round top part, such that an utmost effective AR value of 1.73 is reached. In BF Cu‐plating, two sub‐three‐electrode electrochemical cells are employed to realize equal metal finger heights on both sides of the wafer. Compared to our low thermal‐budget screen‐printing metallization, the Cu‐plated silicon heterojunction devices show both optical and electrical advantages (based on lab‐scale tests). The champion BF Cu‐plated device shows a front‐side efficiency of 22.1% and a bifaciality factor of 0.99.
7 citations
TL;DR: In this paper , the authors investigate front side textures for perovskite/silicon tandem solar cells and show that a simple texture with steepness of only 23° can be more optically efficient than conventional textures with more than double that steepness.
Abstract: We investigate gentle front side textures for perovskite/silicon tandem solar cells. These textures enhance the absorption of sunlight, yet are sufficiently gentle to allow deposition of an efficient perovskite top cell. We present a tandem solar cell with such gentle texture, fabricated by Kaneka corporation, with an efficiency as high as 28.6%. We perform an extensive ray-optics study, exploring non-conformal textures at the front and rear side of the perovskite layer. Our results reveal that a gentle texture with steepness of only 23° can be more optically efficient than conventional textures with more than double that steepness. We also show that the observed anti-reflective effect of such gentle textures is not based a double bounce, but on light trapping by total internal reflection. As a result, the optical effects of the encapsulation layers play an important role, and have to be accounted for when evaluating the texture design for perovskite/silicon tandems.
7 citations
TL;DR: In this article, the average irradiation on the Dutch highway network is around 880kWh/m2/y, 35% less than the potential of an optimally tilted conventional PV system in the south of the Netherlands.
7 citations
TL;DR: In this article , the effects of deposition temperature on passivation quality and SHJ solar cell performance were investigated with Fourier transform infrared spectroscopy (FTIR), and the optimum trade-off between VOC and FF for the SHJ cells was found with temperatures ranging from 160°C to 180°C, which delivered independently certified efficiencies of 23.71%.
Abstract: Excellent surface passivation induced by (i)a-Si:H is critical to achieve high-efficiency silicon heterojunction (SHJ) solar cells. This is key for conventional single-junction cell applications but also for bottom cell application in tandem devices. In this study, we investigated the effects of (i)a-Si:H deposition temperature on passivation quality and SHJ solar cell performance. At the lower end of temperatures ranging from 140°C to 200°C, it was observed with Fourier-transform infrared spectroscopy (FTIR) that (i)a-Si:H films are less dense, thus hindering their surface passivation capabilities. However, with additional hydrogen plasma treatments (HPTs), those (i)a-Si:H layers deposited at lower temperatures exhibited significant improvements and better passivation qualities than their counterparts deposited at higher temperatures. On the other hand, even though we observed the highest VOCs for cells with (i)a-Si:H deposited at the lowest temperature (140°C), the related FFs are poorer as compared to their higher temperature counterparts. The optimum trade-off between VOC and FF for the SHJ cells was found with temperatures ranging from 160°C to 180°C, which delivered independently certified efficiencies of 23.71%. With a further improved p-layer that enables a FF of 83.3%, an efficiency of 24.18% was achieved. Thus, our study reveals two critical requirements for optimizing the (i)a-Si:H layers in high-efficiency SHJ solar cells: (i) excellent surface passivation quality to reduce losses induced by interface recombination and simultaneously (ii) less-defective (i)a-Si:H bulk to not disrupt the charge carrier collections.
4 citations
TL;DR: In this article , the metal polysilicon recombination current density (J 0met) and contact resistivity were measured for planar or saw damage etched (SDE), chemically polished in acidic solution and alkaline pyramidal textured.
Abstract: Passivated contact based on a thin interfacial oxide and a highly doped polysilicon layer has emerged as the next evolutionary step to increase the efficiencies of industrial silicon solar cells. To take maximum advantage from this layer stack, it is vital to limit the losses at the metal polysilicon interface, which can be quantified as metal polysilicon recombination current density (J 0met) and contact resistivity. In cell concepts, wherein a large variety of silicon substrate surface finish can be obtained, it is essential to know how the surface finish affects the J 0met and contact resistivity. Herein, commercially available fire through silver paste and the metal‐polysilicon recombination current densities and contact resistivity are used for three different silicon substrate surface finishes, namely: planar or saw damage etched (SDE), chemically polished in acidic solution and alkaline pyramidal textured. Contact resistivity values below 3 mΩ cm2 with J 0met in order of the recombination current density of the doped region (J 0pass) are obtained for samples with planar surface for both 150 and 200 nm n+ polysilicon layer thicknesses. The results presented in this work show that the samples with flat substrate morphology outperform the samples with textured surfaces.
4 citations
TL;DR: In this paper , the authors quantified the existing relation between irradiance variations and efficiency loss of the logic of the Perturb-and-Observe MPPT algorithm, along with the sensitivity of the MPPT to its control parameters.
Abstract: Irradiance variability is one of the main challenges for using photovoltaic energy. This variability affects the operation of maximum power point trackers (MPPT) causing energy losses. The logic of the Perturb-and-Observe MPPT algorithm is particularly sensitive to quick irradiance changes. We quantified the existing relation between irradiance variations and efficiency loss of the logic of the Perturb-and-Observe MPPT algorithm, along with the sensitivity of the MPPT to its control parameters. If the algorithm parameters are not tuned properly, its efficiency will drop to nearly 2%. Irradiance variability causes a systematic energy loss of the algorithm that can only be quantified by ignoring the hardware components. With this, we aim to improve the energy yield estimation by providing an additional efficiency loss to be considered in the calculations.
3 citations
1 citations
TL;DR: In this article , the morphology and Raman response of nanoscale shaped surfaces of Si substrates versus monocrystalline Si were compared and the rise in the Raman signal was 12-14 × , which is in agreement with the model of the electric field at the tips of Si due to their geometry.
1 citations
TL;DR: In this article , the authors investigated the passivation quality and electrical contact properties for samples with a 150 nm thick n+ polysilicon layer in comparison to samples with an interfacial oxide underneath it.
Abstract: In this article, we investigate the passivation quality and electrical contact properties for samples with a 150 nm thick n+ polysilicon layer in comparison to samples with a phosphorus diffused layer. High level of passivation is achieved for the samples with n+ polysilicon layer and an interfacial oxide underneath it. The contact properties with screen-printed fire-through silver paste are excellent (no additional recombination from metallization and specific contact resistivity (ρc) ≤ 2 mΩ·cm2) for the samples with the polysilicon layers. Fast-firing peak temperature was varied during the contact formation process; this was done to see the trend in the contact properties with the change in the thermal budget. The differences in the J0met and ρc for the two different kinds of samples are explained with the help of high-resolution scanning electron microscope imaging. Finally, we prepare M2-sized n-passivated emitter rear totally (PERT) diffused solar cells with a 150 nm thick n+ polysilicon based passivated rear contact. The best cell achieved an efficiency of 21.64%, with a Voc of 686 mV and fill factor of 80.2%.
TL;DR: In this article , a screen printable Cu paste is used to meetallize industrial interdigitated back contact (IBC) solar cells, which is applied to replace the majority of the Ag used in IBC cells as busbars and fingers.
Abstract: The high usage of silver in industrial solar cells may limit the growth of the solar industry. One solution is to replace Ag with copper. A screen printable Cu paste is used herein to metallize industrial interdigitated back contact (IBC) solar cells. A novel metallization structure is proposed for making solar cells. Cu paste is applied to replace the majority of the Ag used in IBC cells as busbars and fingers. Cu paste is evaluated for use as fingers, and solar cells are made to test conversion efficiency and reliability. The Cu paste achieves comparably low resistivity, and Cu paste printed cells demonstrate similar efficiency to Ag paste printed cells, with an average efficiency of 23%, and only 4.5 mg W−1 of Ag usage. Also, the solar cells are stable and no Cu in‐diffusion is observed under damp heat (85 °C, 85% relative humidity) and thermal stress (200 °C) for 1000 h, respectively. All processes used in this study can be carried out with industrial equipment. These findings reveal a new application for Cu pastes and point to a new direction for reducing Ag utilization and cost.
TL;DR: In this paper , Van Nijen et al. explore the possibility of integrating power electronic components into crystalline silicon solar cells and propose various new design possibilities for PV-cell-integrated diodes, transistors, capacitors, and inductors.
Abstract: Power electronics traditionally plays a crucial role in conditioning the power of photovoltaic (PV) modules and connecting the systems to the electricity grid. Recently, PV module designs with more sub-module power electronics are gaining increased attention. These designs can offer higher reliability and improved resilience against non-uniform illumination. In this review, we explore an innovative method to facilitate sub-module power electronics, which is to integrate the power components into crystalline silicon (c-Si) PV cells. This approach has the potential to enable numerous design innovations. However, the fabrication processes of the integrated power electronics should be compatible with the PV cell fabrication methods. Moreover, only a limited amount of additional processing steps can be added with respect to standard solar cell manufacturing processes to achieve a cost-effective design. After reviewing previous research on this topic, we propose various new design possibilities for PV-cell-integrated diodes, transistors, capacitors, and inductors. Furthermore, we discuss the technical trade-offs and challenges that need to be overcome for successful industry adoption. In this work, Van Nijen et al. explore the possibility of integrating power electronic components into crystalline silicon solar cells. The progress, benefits, possibilities, and challenges of this approach are investigated. Integration of power components into solar cells could enable numerous design innovations in photovoltaic modules and systems.
TL;DR: In this article , the effect of climate on yield prediction using machine learning is unknown and the authors aim to find climatic trends by predicting the power of 48 PV systems around the world, equally divided into four climates.
Abstract: Machine learning is arising as a major solution for the photovoltaic (PV) power prediction. Despite the abundant literature, the effect of climate on yield predictions using machine learning is unknown. This work aims to find climatic trends by predicting the power of 48 PV systems around the world, equally divided into four climates. An extensive data gathering process is performed and open‐data sources are prioritized. A website www.tudelft.nl/open-source-pv-power-databases has been created with all found open data sources for future research. Five machine learning algorithms and a baseline one have been trained for each PV system. Results show that the performance ranking of the algorithms is independent of climate. Systems in dry climates depict on average the lowest Normalized Root Mean Squared Error (NRMSE) of 47.6 %, while those in tropical present the highest of 60.2 %. In mild and continental climates the NRMSE is 51.6 % and 54.5 %, respectively. When using a model trained in one climate to predict the power of a system located in another climate, on average systems located in cold climates show a lower generalization error, with an additional NRMSE as low as 5.6 % depending on the climate of the test set. Robustness evaluations were also conducted that increase the validity of the results.
05 Jun 2022
TL;DR: In this article , the capacitance of four different industrial c-Si PV cell technologies, namely Al-BSF, PERC, IBC, and SHJ, was reported for operation at maximum power point.
Abstract: In conditions of partial shading, the deployment of sub-module maximum power point tracking is known to increase the energy yield of crystalline silicon (c-Si) based photovoltaic (PV) modules. To facilitate PV module designs endowed with an increasing granularity of sub-module power converters, it could be advantageous to exploit the impedance of the c-Si PV cells. For example, it is well known that c-Si PV cells exhibit capacitive effects. However, for such applications, it is critical that the self-capacitance of the PV cells is large enough. As of yet, there are no reports that give a clear overview of the self-capacitance that can be expected for modern industrial c-Si cell technologies. In this work, we report the capacitance of four different industrial c-Si PV cell technologies, namely Al-BSF, PERC, IBC, and SHJ. These capacitance values are obtained by fitting a dynamic model of the solar cell to measurements obtained using impedance spectroscopy in dark conditions. It was found that depending on the cell technology, capacitances in the range of 0.5-6 mF/cm2 can be expected for operation at maximum power point. Our results show that there is a high potential to remove the input capacitors from sub-module power converters in PV applications, due to the fact that the ripple voltage at the input of the converter is naturally suppressed by the PV self-capacitance.
TL;DR: In this article , optical filters and phase change materials were used to reduce the operating temperature of photovoltaic (PV) modules in a building in Delft, Netherlands.
Abstract: When integrated into urban environments, photovoltaic (PV) systems usually present operational temperatures that are significantly higher than those shown by rack-mounted systems. High operating temperatures are associated with reduced reliability of PV modules and significantly impact the electrical performance of solar cells. Utilizing the heat produced on PV modules or reducing operating temperatures can bolster their application within the building sector. We present the three main concepts studied to achieve these goals. First, a PV is a chimney concept that allows the use of the heat generated by the modules. Simulations for a PV chimney installed on a building in the Netherlands showed that although the heat quality produced inside its cavity was low, the potential use of the air mass flow for ventilation applications is promising. Additionally, we present two passive cooling solutions that can reduce the operating temperatures of PV modules: Optical filters and phase change materials. Experimental measurements in Delft showed that these solutions reduce the operating temperature of PV modules between 4 °C to 20 °C, particularly under high irradiance hours.
05 Jun 2022
TL;DR: In this article , the authors investigated the effects of (i)a-Si:H deposition temperature on passivation quality and solar cell performance, and they found that with additional hydrogen plasma treatments (HPTs), those layers exhibited significant improvements and better passivation qualities than their higher temperature counterparts.
Abstract: Excellent surface passivation induced by (i)a-Si:H is critical to achieve high-efficiency silicon heterojunction (SHJ) solar cells. In this study, we investigated the effects of (i)a-Si:H deposition temperature on passivation quality and solar cell performance. Among the deposition temperatures we investigated ${(140\ -200^{\mathrm{o}}\mathrm{C})}$, lower temperatures seem to result in less dense (i)a-Si:H films, which hinder their surface passivation capabilities. However, with additional hydrogen plasma treatments (HPTs), those (i)a-Si:H layers exhibited significant improvements and better passivation qualities than their higher temperature counterparts. On the other hand, even though we observed the highest VOCs for cells with (i)a-Si:H deposited at the lowest temperature (140 ${{}^{\circ}\mathrm{C})}$, the related FFs are poorer as compared to their higher temperature counterparts. The optimum trade-off between VOC and FF was found with temperatures ranging from ${160^{\circ}\mathrm{C}}$ to ${180^{\circ}\mathrm{C}}$, which delivered independently certified efficiencies of 23.71%. Thus our study reveals two critical requirements for optimizing the (i)a-Si:H layers in high-efficiency SHJ solar cells: (i) excellent surface passivation quality to reduce losses induced by interface recombinations and (ii) less-defective (i)a-Si:H bulk to improve the charge carrier collections.