Publications by Stefaan De Wolf

Below the Urbach Edge: Solar Cell Loss Analysis Based on Full External Quantum Efficiency Spectra

Stefaan De Wolf, Jakub Holovsky, Randall Ellingson, Xin Yu Chin

We suggest a new solar cell loss analysis using theexternal quantumefficiency (EQE) measured with sufficiently high sensitivity to alsoaccount for defects. Unlike common radiative-limit methods, wherethe impact of deep defects is ignored by exponential ext ...

AMER CHEMICAL SOC2023

Photovoltaics at multi-terawatt scale: Waiting is not an option

Stefaan De Wolf, Sophia Haussener

A major renewable-energy milestone occurred in 2022: Photovoltaics (PV) exceeded a global installed capacity of 1 TWdc. But despite considerable growth and cost reduction over time, PV is still a small part of global electricity generation (4 to 5% for 202 ...

American Association for the Advancement of Science2023

Quantitative Analysis of Nanorough Hydrogenated Si(111) Surfaces through Vibrational Spectral Assignment by Periodic DFT Calculations br

Christophe Ballif, Stefaan De Wolf, Jakub Holovsky

In this work, we use periodic density functional theory(periodic DFT) to rigorously assign vibrational spectra measured on nanorough wet-processed hydrogenated Si(111) surfaces. We compare Si(111)-(1x1) surfaces etched by dilute HF and NH4F, featuring two ...

AMER CHEMICAL SOC2022

Toward Stable Monolithic Perovskite/Silicon Tandem Photovoltaics: A Six-Month Outdoor Performance Study in a Hot and Humid Climate

Christophe Ballif, Quentin Thomas Jeangros, Stefaan De Wolf, Shynggys Zhumagali

Perovskite/silicon tandem solar cells are emerging as a high-efficiency and prospectively cost-effective solar technology with great promise for deployment at the utility scale. However, despite the remarkable performance progress reported lately, assuring ...

AMER CHEMICAL SOC2021

Amorphous/Crystalline Silicon Interface Stability: Correlation between Infrared Spectroscopy and Electronic Passivation Properties

Christophe Ballif, Stefaan De Wolf, Jakub Holovsky, Silvia Martin de Nicolas Agut

Ultrathin layers of hydrogenated amorphous silicon (a-Si:H), passivating the surface of crystalline silicon (c-Si), are key enablers for high-efficiency silicon heterojunction solar cells. In this work, the authors apply highly sensitive attenuated total r ...

WILEY2020

Mitigating Plasmonic Absorption Losses at Rear Electrodes in High‐Efficiency Silicon Solar Cells Using Dopant‐Free Contact Stacks

Christophe Ballif, Quentin Thomas Jeangros, Stefaan De Wolf, Mathieu Gérard Boccard, Julie Amandine Dreon, Sihua Zhong, Fan Fu

Although charge‐carrier selectivity in conventional crystalline silicon (c‐Si) solar cells is usually realized by doping Si, the presence of dopants imposes inherent performance limitations due to parasitic absorption and carrier recombination. The develop ...

2019

Field Performance versus Standard Test Condition Efficiency of Tandem Solar Cells and the Singular Case of Perovskites/Silicon Devices

Christophe Ballif, Stefaan De Wolf, Björn Niesen, Olivier Denis Dupré

Multijunction cells may offer a cost-effective route to boost the efficiency of industrial photovoltaics. For any technology to be deployed in the field, its performance under actual operating conditions is extremely important. In this perspective, we eval ...

2018

Toward Annealing-Stable Molybdenum-Oxide-Based Hole-Selective Contacts For Silicon Photovoltaics

Christophe Ballif, Stefaan De Wolf, Mathieu Gérard Boccard, Jérémie Werner, Jonas Geissbühler, Monica Morales Masis, Philipp Friedrich Hermann Löper, Oscar Esteban Rucavado Leandro, Stephanie Essig, Julie Amandine Dreon

Molybdenum oxide (MoOX) combines a high work function with broadband optical transparency. Sandwiched between a hydrogenated intrinsic amorphous silicon passivation layer and a transparent conductive oxide, this material allows a highly efficient hole‐sele ...

2018

Amorphous gallium oxide grown by low-temperature PECVD

Christophe Ballif, Aïcha Hessler-Wyser, Quentin Thomas Jeangros, Stefaan De Wolf, Mathieu Gérard Boccard, Monica Morales Masis, Eiji Kobayashi, Daniel Vresilovic, Nathan Jacques Rodkey

2018

Hole-Collection Mechanism in Passivating Metal-Oxide Contacts on Si Solar Cells: Insights From Numerical Simulations

Christophe Ballif, Stefaan De Wolf, Philipp Friedrich Hermann Löper, Stephanie Essig

2018

Interdigitated back contact silicon heterojunction solar cells featuring an interband tunnel junction enabling simplified processing

Christophe Ballif, Antoine Descoeudres, Nicolas Badel, Benjamin Strahm, Antonin Faes, Sylvain Nicolay, Quentin Thomas Jeangros, Gabriel Christmann, Stefaan De Wolf, Matthieu Despeisse, Loris Barraud, Jonas Geissbühler, Johannes Peter Seif, Andrea Tomasi, Bertrand Yves Paul Paviet-Salomon

This paper reports on the development of an innovative back-contacted crystalline silicon solar cell with passivating contacts featuring an interband tunnel junction at its electron-collecting contacts. In this novel architecture, named "tunnel-IBC", both ...

2018

The impact of silicon solar cell architecture and cell interconnection on energy yield in hot & sunny climates

Christophe Ballif, Jacques Levrat, Stefaan De Wolf, Matthieu Despeisse, Jean Cattin, Yannick Samuel Riesen, Johannes Peter Seif, Andrea Tomasi, Jan Haschke, Brahim Aissa

Extensive knowledge of the dependence of solar cell and module performance on temperature and irradiance is essential for their optimal application in the field. Here we study such dependencies in the most common high-efficiency silicon solar cell architec ...

Royal Soc Chemistry2017

Optical Evaluation of the Rear Contacts of Crystalline Silicon Solar Cells by Coupled Electromagnetic and Statistical Ray-Optics Modeling

Christophe Ballif, Ali Dabirian, Stefaan De Wolf, Franz-Josef Haug, Monica Morales Masis

High-efficiency crystalline silicon (c-Si) solar cells increasingly feature sophisticated electron and hole contacts aimed at minimizing electronic losses. At the rear of photovoltaic devices, such contacts-usually consisting of stacks of functional layers ...

Ieee-Inst Electrical Electronics Engineers Inc2017

Improved Optics in Monolithic Perovskite/Silicon Tandem Solar Cells with a Nanocrystalline Silicon Recombination Junction

Christophe Ballif, Aïcha Hessler-Wyser, Sylvain Nicolay, Quentin Thomas Jeangros, Stefaan De Wolf, Matthieu Despeisse, Jérémie Werner, Florent Sahli, Loris Barraud, Raphaël Monnard, Johannes Peter Seif, Andrea Tomasi, Bertrand Yves Paul Paviet-Salomon, Björn Niesen, Matthias Wolfgang Bräuninger

Perovskite/silicon tandem solar cells are increasingly recognized as promi-sing candidates for next-generation photovoltaics with performance beyond the single-junction limit at potentially low production costs. Current designs for monolithic tandems rely ...

2017

Impact of organic overlayers on a-Si:H/c-Si surface potential

Christophe Ballif, Stefaan De Wolf, Johannes Peter Seif, Andrea Tomasi, Björn Niesen

Bilayers of intrinsic and doped hydrogenated amorphous silicon, deposited on crystalline silicon (c-Si) surfaces, simultaneously provide contact passivation and carrier collection in silicon heterojunction solar cells. Recently, we have shown that the pres ...

American Institute of Physics2017

Increasing the efficiency of silicon heterojunction solar cells and modules by light soaking

Christophe Ballif, Antoine Descoeudres, Jacques Levrat, Stefaan De Wolf, Franz-Josef Haug, Matthieu Despeisse, Eiji Kobayashi

Silicon heterojunction solar cells use crystalline silicon (c-Si) wafers as optical absorbers and employ bilayers of doped/intrinsic hydrogenated amorphous silicon (a-Si:H) to form passivating contacts. Recently, we demonstrated that such solar cells incre ...

Elsevier Science Bv2017

Transparent Electrodes for Efficient Optoelectronics

Christophe Ballif, Stefaan De Wolf, Monica Morales Masis, Rachel Emma Woods-Robinson

With the development of new generations of optoelectronic devices that combine high performance and novel functionalities (e.g., flexibility/bendability, adaptability, semi or full transparency), several classes of transparent electrodes have been develope ...

2017

Photocurrent Spectroscopy of Perovskite Layers and Solar Cells: A Sensitive Probe of Material Degradation

Christophe Ballif, Stefaan De Wolf, Jérémie Werner, Jakub Holovsky, Björn Niesen, Martin Ledinsky, Philipp Friedrich Hermann Löper, Martin Müller

Optical absorptance spectroscopy of polycrystalline CH3NH3PbI3 films usually indicates the presence of a PbI2 phase, either as a preparation residue or due to film degradation, but gives no insight on how this may affect electrical properties. Here, we app ...

Amer Chemical Soc2017

Simple processing of back-contacted silicon heterojunction solar cells using selective-area crystalline growth

Christophe Ballif, Antoine Descoeudres, Sylvain Nicolay, Quentin Thomas Jeangros, Gabriel Christmann, Stefaan De Wolf, Matthieu Despeisse, Loris Barraud, Johannes Peter Seif, Andrea Tomasi, Bertrand Yves Paul Paviet-Salomon, Jan Haschke

For crystalline-silicon solar cells, voltages close to the theoretical limit are nowadays readily achievable when using passivating contacts. Conversely, maximal current generation requires the integration of the electron and hole contacts at the back of t ...

Nature Publishing Group2017

Imaging the Spatial Evolution of Degradation in Perovskite/Si Tandem Solar Cells After Exposure to Humid Air

Christophe Ballif, Stefaan De Wolf, Jérémie Werner, Florent Sahli, Björn Niesen, Randall Ellingson

Monolithically integrated two-terminal perovskite/Si tandem solar cells promise to achieve high power conversion efficiency. However, there is a concern that the stability of the perovskite top cell will limit the long-term performance of tandem devices. T ...

Ieee-Inst Electrical Electronics Engineers Inc2017