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The present study investigates the application of hole-selective transition metal oxide (TMO) layers (MoOx, V2Ox, and WOx) with silver (Ag) as full-area rear contact to 22.5 mu m-thick low-quality Cz p-type c-Si solar cells. Thin films of metal oxides are deposited directly on p-type c-Si by thermal evaporation at room temperature. The large work function of these TMOs creates strong accumulation at the interface with p-type c-Si, which allows only holes to transport and simultaneously suppress the interfacial recombination current density (J(0)) and contact resistivity (rho(c)). The current generation and losses of 22.5 mu m-thick solar cells with different hole-selective TMO/Ag at the rear are simulated. The presence of TMO/Ag at the rear is found to significantly reduce parasitic light absorption at longer wavelengths which becomes more pronounced for ultrathin wafers, providing significant advantages over conventional Al contact. The best device performance was attained by the MoOx/p-type c-Si solar cells, demonstrating a considerably high efficiency (eta) of 14% with V-oc of 555 mV, FF of 76.0%, and J(sc) of 33.2 mA/cm(2). Furthermore, the present work is the first to employ MoOx, V2Ox, and WOx as rear contact in ultrathin p-type c-Si solar cells.

In this study, we report on the passivation quality of atomic layer deposition grown ultra-thin Al2O3 and Al2O3 capped with plasma-enhanced chemical vapor deposition deposited SiNx on Cz p-type wafers for the rear side of a passivated emitter and rear cell (PERC). Different activation recipes using N-2, forming gas (FG), and two-step annealing for different durations are investigated before SiNx deposition. The effect of different Al2O3 thicknesses and corresponding activation processes on the Al2O3/SiNx passivation performance, after a high temperature firing step, is studied to reach a new optimization toward higher efficiency and lower cost. A record high iV(oc) of 720mV is obtained after firing step from Al2O3/SiNx stacks with Al2O3 thickness as thin as similar to 2nm with FG annealing. Our results demonstrate that, under well-optimized process conditions, ultra-thin Al2O3 thicknesses provide superior passivation quality as compared to the larger thicknesses which are commonly applied in the PERC industrial line and the potential for further improvement of industrial PERC solar cells in terms of cost reduction and efficiency.

We present the feasibility of integrating substoichiometric molybdenum oxide (MoOx) as hole-selective rear contact into the production sequence of industrial scale p-type crystalline silicon (c-Si) solar cells. Thin films of MoOx are deposited directly on p-type c-Si by thermal evaporation at room temperature. It is found that Ag/MoOx/p-type c-Si rear contact structure exhibits low contact resistivity and modest surface recombination current density. The attained peak efficiency (eta) of the fabricated solar cells is 17.65% with V-oc of 626 mV, J(sc) of 36.8 mA/cm(2), and fill factor (FF) of 76.63%. Next, a complete loss analysis of a MoOx/p-type Si heterojunction solar cell is carried out for the first time by using Quokka simulation software that employs characteristics of different layers which constitute the fabricated solar cell. Based on this loss analysis, the dominant loss mechanisms are defined and a roadmap to attain the desired highest possible efficiency from industrial scale p-type c-Si solar cells with full-area MoOx hole-collecting rear contact is explored.

Conventional silicon heterojunction solar cells employ defects-prone a-Si:H layers for junction formation and passivation purposes. Substituting these layers with hole-selective MoO(x)and electron-selective TiO(x)can reduce parasitic absorption and energy band offsets issues associated with doped silicon films. In this work, dopant-free asymmetric heterostructure Si solar cells are studied with and without SiO(2)passivation layer, and their performance has been compared. The inclusion of ultrathin SiO(2)insulator as a passivation layer promotes significant band bending that induces interface inversion of crystalline silicon as well as maintains the electric field required to tunnel charge carriers. The energy band diagram studies and variation of oxide thickness show that the IV characteristics of the solar cell critically depend on the insulator thickness; as the carriers tunnelling through the insulator becomes negligible at larger thicknesses. The simulated structure with MoO(x)as front hole-selective contact and without any passivation exhibited conversion efficiency of 15.73%, which improved to 18.69% by incorporating passivated a-Si:H. However, by employing rear SiO2/TiO(x)stack with the front SiO2/MoOx, the device performance enhanced to open-circuit voltage of 785 mV, short-circuit current density of 41 mA/cm(2), fill factor of 77%, and simulated conversion efficiency of 24.83%, which is similar to 10% enhancement in the performance as compared to reference device employing traditional a-Si:H with dopant-free films.

Dopant-free carrier-selective transition metal oxide (TMO) contacts offer unique electrical properties pertaining to the rectification of doping-related issues in silicon (cSi) solar cell. In this paper, cSi heterojunction solar cell featuring TMOs of molybdenum oxide (MoOx) and titanium oxide (TiOx) as hole- and electron-selective contacts, respectively, has been realized using Silvaco TCAD. The photovoltaic performance has been evaluated based on the electron affinity of TiOx, its thickness, interfacial charge density, band gap, and operating temperature. MoOx with an appropriate work function prompts band bending leading to Fermi level pinning at top interface. Insertion of TiOx with low electron affinity reduces the rear energy barrier against electrons from 0.86 eV to 0.15 eV. Minimum recombination has been observed for electron affinity values range of 3.6-4.2 eV. The rear interface defects (D-it) should be minimized to reduce the recombination and to facilitate transportation of electrons. The device numerically demonstrated V-oc of 723 mV, J(sc) 39.2 mA/cm(2), FF 79.8%, and eta of 22.64% with temperature coefficient of -0.08%/degrees C. These results validate the applicability of heterojunction design with fully-covered carrier-selective contacts that can be useful for industrial applications as it eliminates the need of doped layers with the associated capital-intensive and complicated fabrication processes. (C) 2019 Elsevier Ltd. All rights reserved.

Surface texturing of transparent conductive oxides is crucial to improve the fraction of incident light trapped in the absorber layer of thin film silicon based solar cells to improve the device performance. In this work, we fabricate and compare periodic, overlapping, and random surface textures and patterns on aluminium doped zinc oxide (AZO) using direct laser processing. The effects of the used laser wavelength, laser operating frequency, and pulse periodicity on the structural, morphological, and optical response of the AZO films were investigated. By optimizing the laser parameters and the associated process conditions, a drastic increase up to 60% in the transmittance haze over the entire solar was achieved.

In this work, we demonstrate a strong correlation between crystalline silicon (cSi) base doping concentration and the performance of cSi/MoOx heterojunction solar cell by investigating the structure numerically based on Silvaco TCAD simulation tool and experimentally. The doping concentration of n-type cSi was scanned in the 1 x 10(15) - 2 x 10(16) cm(-3) range. Simulation results show that utilizing highly doped cSi wafer degrades the conversion efficiency of cSi/MoOx solar cell. Efficiency of 11.16% has been obtained from simulation results for 1 x 10(15) cm(-3) doping concentration while this value reduces to less than 4% for wafer with a doping concentration of 2 x 10(16) cm(-3). These simulation results were demonstrated experimentally and n-type cSi wafers with two different doping concentrations were considered, 1 x 10(15) and 5.5 x 10(15) cm(-3). The key concept underlying this work is to differentiate explicitly the effect of cSi doping concentration on the performance of cSi/MoOx cell, thus a simple cell design is considered where n-type cSi wafers were heavily phosphorous-doped to form (n(+)) at the front of the Si and thermally evaporated MoOx films with various thicknesses (

Single and double plasmonic interfaces consisting of silver nanoparticles embedded in media with different dielectric constants including SiO2, SiNx, and Al:ZnO have been fabricated by a self-assembled dewetting technique and integrated to amorphous silicon films. Single plasmonic interfaces exhibit plasmonic resonances whose frequency is red-shifted with increasing particle size and with the thickness of a dielectric spacer layer. Double plasmonic interfaces consisting of two different particle sizes exhibit resonances consisting of double minima in the transmittance spectra. The optical extinction of a-Si:H deposited on these interfaces is broadened into the red indicating higher absorption and/or scattering at wavelengths higher than those typically absorbed by a-Si:H without plasmonic interfaces. While the photocurrent shows an overall decrease for the samples with the interfaces, significant enhancement of photocurrent is observed near the low-energy edge of the bandgap (600-700 nm). These results correlate well with the broadened extinction spectra of the interfaces and are interpreted in terms of enhanced absorption in that region.

Incident photon conversion efficiency of the absorbing materials at either side of a thin film solar module can be enhanced by integrating a plasmonic interface. Silver nanoparticles represent a good candidate that can be integrated to a thin film solar cell for efficient light-trapping. The aim of this work is to fabricate plasmonically active interface consisting of Ag nanoparticles embedded in Al:ZnO that has the potential to be used at the front surface and at the back reflector of a thin film solar cell to enhance light-trapping and increase the photoconversion efficiency. We show that Ag can readily dewet the Al:ZnO surface when annealed at temperatures significantly lower than the melting temperature of Ag, which is beneficial for lowering the thermal budget and cost in solar cell fabrication. We find that such an interface fabricated by a simple dewetting technique leads to plasmonic resonance in the visible and near infrared regions of the solar spectrum, which is important in enhancing the conversion efficiency of thin film solar cells.