Silicon Heterojunction Solar Cells on Quasi-mono Wafers

Brahim Aissa, Christophe Ballif, Loris Barraud, Mathieu Gérard Boccard, Antoine Descoeudres, Matthieu Despeisse, Jan Haschke, Raphaël Monnard
IEEE, 2018
Article de conférence

Résumé

We applied hydrogen passivation, gettering and a combination of both to quasi-mono (qm) wafer material to enhance its bulk lifetime and prepared silicon heterojunction (SHJ) solar cells. We find that while our applied hydrogen passivation alone seems not to enhance lifetime, a gettering treatment increases bulk lifetime so that efficiencies up to 21.5% were achieved with a SHJ solar cell. This is close to the highest efficiency reported for such a cell. We find that the variation of the absorber thickness plays a minor role for the investigated solar cells and that similar efficiencies could have been obtained for Cz and gettered qm wafers. The latter is mainly due to the fact that the higher efficiency potential of the Cz material could not be fully exploited due to a degradation of surface passivation during the sputtering of the TCO on the cell, which could not be fully recovered in the final annealing step.

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https://infoscience.epfl.ch/record/267425?ln=fr

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Brahim Aissa, Christophe Ballif, Loris Barraud, Mathieu Gérard Boccard, Antoine Descoeudres, Matthieu Despeisse, Jan Haschke, Raphaël Monnard
IEEE, 2018
Article de conférence

Résumé

Official source

https://infoscience.epfl.ch/record/267425?ln=fr

À propos de ce résultat

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Silicon Heterojunction Solar Cells on Quasi-mono Wafers

Brahim Aissa, Christophe Ballif, Loris Barraud, Mathieu Gérard Boccard, Antoine Descoeudres, Matthieu Despeisse, Jan Haschke, Raphaël Monnard

IEEE2018

Chargement

Investigation on the impact of passivation in perovskite solar cells

Erfan Shirzadi

Conversion of sunlight to electricity is the most plausible approach towards the generation of renewable energies. During recent decade lead halide perovskites (LHPs) have proven to be promising candidates for photovoltaic applications such as solar cells. LHPs can be made easily in laboratories around the world via solution process methods and many universities can afford to participate in their development. How-ever, LHPs suffer from instability issues and their efficiencies can be further improved. In this thesis, both instability and efficiency challenges are addressed. We showed by doping the precursor of methylammonium lead iodide (MAPbI3) perovskite with a relatively large cation of 2-Choloroethylammonium (CLEA), perovskites films with CLEA incorporated into their structures are formed. The novel perovskite is able to withstand high temperatures as high as 80°C while achieving efficiencies > 19% in MAPbI3-based perovskite solar cells (PSCs). Various approaches have been employed for the passivation of the defects in perovskite solar cells Vari-ous approaches have been employed to passivate the defects in perovskite films used in perovskite solar cells (PSCs). However, the passivation mechanism is often unclear at a molecular level and the reason for enhanced PSC performance remains elusive. Here, we describe passivation based on the deposition of two dimensional (2D) perovskites (obtained from para-halophenylethylammonium iodide) on the surface of perovskite films. Moreover, the mechanism of passivation was elucidated and was traced to the high work function of the 2D perovskites, which induce band-bending at the surface of perovskite film and therefore reduces the charge carrier recombination at the interface of perovskite and the hole transporting material (HTM). Efficiencies >22% with average voltages >1.15 V were achieved using a typical mesoporous-TiO2 and Spiro-OMeTAD device configuration. This study paves the way for PSCs efficiency improvement by rational design. The employment of 2D perovskites is a promising approach to tackle the stability and voltage issues inherent in perovskite solar cells. It remains unclear however whether other perovskites with different dimensionalities have the same effect on efficiency and stability. Here, we report the use of quasi-3D azetidinium lead iodide (AzPbI3) as a secondary layer on top of the primary 3D perovskite film that results in significant improvements in the photovoltaic parameters. Remarkably, utilization of AzPbI3 leads to the passivation resulting in a power conversion efficiency (PCE) of 22.4 %. The open-circuit voltage obtained is as high as 1.18 V, which is among the highest reported to date for single-junction perovskite solar cells, corresponding to a voltage deficit of 0.37 V for a bandgap of 1.55 eV. Studying the compositional instability of mixed ion perovskites under light illumination is important to understand the mechanisms underlying their efficiency and stability. However, current techniques are limited in resolution and are unable to deconvolute minor ion migration phenomena. Here, we describe a method that enables ion migration to be studied allowing different segregation mechanisms to be elucidated. We applied statistical analysis to cathodoluminescence data to generate compositional distribution histograms. Using these histograms, we identified two different ion migration phenomena, horizontal ion migration (HIM) and vertical ion migration (

EPFL2021

Chargement

Today more than ever the world needs clean energy sources and thus a fast deployment and scaling up of the photovoltaic industry. In this context improving solar cell efficiency plays a major role. In order to achieve the maximum single junction efficiency for this material, technologies featuring carrier selective passivating contacts are foreseen to be the next successors of actual industrial cells. Among them, the silicon heterojunction (SHJ) solar cell is a promising technology which demonstrated efficiencies up to 26.7%. Its main specificity consists in the use of intrinsic and doped amorphous silicon (a-Si:H) to provide surface passivation and carrier selectivity to the c-Si, which allows to reach very high operating voltages in comparison to other c-Si based technology. The major drawbacks of SHJ solar cell is the large parasitic absorption occurring in those layers. To address this challenge, a strong focus on alternative non-silicon based thin films with wider band gap has built up in the literature. A first part of this thesis focuses on reviewing the fundamental process behind carrier selectivity and discuss the ability of different models from the literature to draw informations directly from the peculiar shapes of IV curves commonly observed in the solar cells featuring newly developed materials. We first discuss the simple four ideal diodes model of Roe et al to explain the occurrence of S-shapes depending on the contact quality. We discuss from a theoretical point of view how to improve the model by modifying the ideal diodes by other circuit elements as well as adding bulk recombinations. We test the theory experimentally and identified modifications that should be incorporated in the model.In a second part of the thesis, we explore the development of doped nano-crystalline silicon (nc-Si) layers to replace classical amorphous silicon layers. We investigate the influence of TMB and BF3 as dopant sources on the transparency and contact properties of nc-Si:H(p) layers as well as their integration in solar cells. We expose the roles of both gas to modify the crystallinity of the layer and find different optimum for both of them to lead high efficiencies, illustrated by a certified 23.9%-efficient solar cell. We report also on further optimization steps of this front junction architecture resulting in certified efficiency of 24.44%.We explore next the n-type nc-Si layers for application as window layer. In particular, we perform thickness and doping series to unravel the layer properties along its growth direction. In order to improve the low doping of the nucleation zone of nc-Si:H(n) at the i/n interface, a thin a-Si:H(n) buffer layer is introduced and shown to improve the passivation, selectivity and contact resistivity. Finally, we also report on the beneficial effect of an additional SiOx capping layer which improves both the reflection properties as well as all contact properties, broadening the optimal parameter window. The absorption loss in the front silicon layers remains however the highest share of losses, and therefore we explore theoretically the opportunity of using thinner front side layers or using thin TCO / silicon nitride bilayers to reduce the absorption losses. We finish the discussion by presenting an optimization roadmap, showing a possibility for double-side contacted SHJ cells to reach efficiencies above 26% without requiring any patterning or localization step.

EPFL2022

Chargement

Investigation on the impact of passivation in perovskite solar cells

Erfan Shirzadi

EPFL2021

EPFL2022