About

David Hwang is an Associate Professor in the Department of Mechanical Engineering at Stony Brook University. He earned his Ph.D. from the University of California at Berkeley in 2005. His research focuses on micro and nanoscale heat transfer, laser-assisted solar photovoltaic manufacturing and diagnostics, and advanced diagnostics of light-matter interaction. His work involves exploring the fundamental mechanisms of heat transfer at small scales and developing innovative techniques for manufacturing and diagnostics in solar energy and photonics applications.

Research topics

• Optoelectronics
• Nanotechnology
• Materials science
• Condensed matter physics
• Physics
• Chemistry
• Composite material
• Optics

Selected publications

• INVESTIGATION OF LASER SCRIBING MECHANISMS FOR METALLIC THIN FILMS ON A FLEXIBLE SUBSTRATE TOWARDS PHOTOVOLTAIC SOLAR MODULE MANUFACTURING

  2026-01-01

  article1st authorCorresponding
  PublisherDOI

• Enhancing low-temperature sintering in the MgO-LiF system: Mechanistic insights

  Journal of the European Ceramic Society · 2025-11-26 · 1 citations

  articleOpen access

  In the present article, we provide compelling evidence that minor (1 wt%) additions of micron and nanometre-sized LiF particles in MgO decompose leading to free Li diffusing into MgO surfaces enhancing vacancy production during direct current sintering. The addition of nanometre-sized LiF particles leads to a > 500 °C reduction in the sintering temperature and over 99 % theoretical density of final consolidated compacts. Correlating differential scanning calorimetry with in-situ x-ray diffraction, together with Schottky calculations, post sintering electron microscopy and laser induced breakdown spectroscopy, we uncover critical insights into this impressive reduction in sintering temperature. Our quantitative analysis reveals that MgO and LiF interact at low temperatures with the diffusion of Li into the surface of MgO particles due to the intrinsic structural disorder of the LiF and MgO crystallites. Nanometre-sized LiF particles were found to react the most at low temperatures due to their increased structural disorder. Our multimodal characterization points to a Li-promoted densification and sintering mechanism. This impressive reduction in sintering temperature can be harnessed to promote low-temperature fabrication of MgO-based composites for technological applications.

  PublisherDOI

• Unveiling Mechanisms of Nano‐ and Picosecond Laser Scribing of Bilayer Molybdenum Thin Films on Flexible Polyimide for CuIn_<i>x</i>Ga_{(1−<i>x</i>)}Se₂ Solar Photovoltaic Module Fabrication

  Solar RRL · 2025-04-03 · 1 citations

  articleOpen accessSenior authorCorresponding

  Flexible CuIn x Ga (1 −x ) Se 2 (CIGS) thin‐film solar cells are promising for future applications in buildings, mobility, and aerospace due to their high efficiency, lightweight, and flexible nature. To achieve large‐area monolithic‐integrated modules, a scribing process, dividing into multiple cells for series connection, is indispensable. Despite numerous merits laser scribing can offer, further improvement is required for high‐quality solar module. Picosecond laser, generally accepted as an efficient tool to suppress thermal impact, often causes problems in achieving a shunt‐free P1 scribing process that isolates the back contact, typically bi‐ or multilayered Mo thin films, due to edge deformation as a source of shunt. In this study, we experimentally compare the performance of picosecond and nanosecond lasers in scribing bilayered Mo films of different microstructures on flexible polyimide through morphological analysis and shunt evaluation for selected scribing conditions. Thermal analysis and time‐resolved measurement of laser‐induced emission further elucidate relevant scribing mechanisms. It will be shown that nanosecond lasers, usually not a preferred solution for temperature‐sensitive architectures, have significant merits in scribing complex multilayered structures of relatively large thickness, preferentially launching indirect interfacial heating mechanism for optically nontransparent film–substrate combinations.

  PublisherOA PDFDOI

• Dynamics of CSR and Employee Retention: A Generational Perspective

  Journal of Accounting Business and Management (JABM) · 2025-11-03

  articleOpen access

  The main objective of this study is to gain insights into the five corporate social responsibility (CSR) factors— environment-related CSR, human rights &amp; labor, product responsibility, community engagement, and corporate governance— and to understand their impact on employee retention among gen X, Y, and Z employees in the workplace during the Covid-19 pandemic. We collected survey data using Amazon Mechanical Turk, with a final sample size of 536 responses. The regression analyses indicated a positive and significant relationship between environment-related CSR and employee retention. The results also suggested that both human rights and labor-related CSR, as well as product responsibility-related CSR, are positively related to higher employee retention. Additionally, generational differences moderated the effect of environment-related CSR on employee retention, with a stronger correlation observed among gen Y and Z employees compared to gen X. These findings help reconcile mixed evidence on CSR–retention links by emphasizing generational differences and offering practical guidance. Managers aiming to retain talent should prioritize environmental stewardship, fair labor practices, and responsible products while tailoring CSR initiatives to the preferences of different employee cohorts.

  PublisherOA PDFDOI

• Laser scribing of flexible thin film photovoltaic solar cells

  2025-01-01

  article1st authorCorresponding
  PublisherDOI

• Selective laser scribing of thin films for photovoltaic solar cell devices

  2025-01-24

  article1st authorCorresponding

  Photovoltaic (PV) solar cells have been one of the most quickly developing renewable energy technologies. To upscale into the module level which will provide desired voltage and power outputs, laser scribing technology has been actively developed taking advantages over mechanical scribing, including reliable and precise scribing capabilities due to non-contact processing nature. Short/ultrashort pulsed lasers have shown favorable trends for layer specific scribing based on versatile thermal/non-thermal mechanisms selectively activated at a wide range of temporal and spatial domains. This study focuses on the manufacturing of build-integrated photovoltaic based on thin film PV architectures on two different platforms; fabrication on flexible substrates that will be attached to the arbitrary building surfaces, and fabrication of see-through patterns on conventional glass substrate in conjunction with relevant scribing mechanisms. On-going study includes efforts for larger scale manufacturing and realization of tandem solar module.

  PublisherDOI

• Highly sensitive and robust soft tri-axial tactile sensors enabled by dual inductive sensing mechanismss

  Soft Science · 2025-01-18 · 7 citations

  articleOpen access

  Tri-axial tactile sensors that provide real-time information on both normal and shear forces are enabling technologies for tactile perception, which open up new possibilities in robotics, human-machine interfaces, environmental sensing, and health monitoring. Among tri-axial tactile sensors based on different mechanisms, inductive sensors possess good robustness against environmental contamination. Their low sensitivity to normal and shear loads, however, is a critical barrier. This work presents the rational design of soft inductive tri-axial tactile sensors that are capable of distinguishing static or dynamic normal and shear loads, with exceptional tactile sensitivity. Dual mechanisms of Biot-Savart law and Eddy current effect are explored to overcome the long-standing sensitivity issue. In addition, a hybrid coil with non-uniform spacing is designed to generate uniform magnetic fields, addressing the limitations of traditional uniform coils and significantly improving the sensor’s tactile sensitivity. The picosecond pulsed laser scribing technique makes it possible to pattern silver nanowires into inductive coils with high fidelity. A porous compressible layer is adopted to enable adjustable sensitivity and sensing range to meet diverse application demands. Finally, the sensor is integrated between the user’s leg and the orthosis, showcasing the sensor’s capability for real-time monitoring of tri-axial forces and its robustness against environmental objects.

  PublisherOA PDFDOI

• Laser Scribing for Perovskite Solar Modules of Long‐Term Stability

  Solar RRL · 2024-03-26 · 14 citations

  articleOpen accessCorresponding

  Although the efficiency of hybrid lead‐halide perovskite solar cells has been significantly improved, the efficiency gap between small‐area cells and large modules continues to be a considerable challenge. Laser scribing is essential for realizing high‐quality monolithic connections; however, the laser‐induced material changes and their correlation with device performance have not been yet well understood, in particular for the perovskite material systems. In this study, the effect of P3 laser processing conditions on device performance and stability is explained. The most interesting finding is an improvement in open‐circuit voltage ( V OC ) after aging and long‐term stability under low‐laser‐overlap conditions that avoid direct laser exposure to perovskite material system as a source of material degradation. It is found that a high‐laser‐overlap during P3 results in a lower fill factor after aging and accelerated degradation due to larger portion of perovskite directly exposed to laser during the scribing process. The increased V OC under low‐overlap conditions is attributed to the increased PbI 2 formation in the P3 region. Moreover, a minimal pulse overlap is favorable for preserving long‐term device stability. Finally, a perovskite minimodule with an efficiency of 20.24% is successfully developed as a result of these findings.

  PublisherOA PDFDOI

• Enhanced Mechanical Stability of CIGS Solar Module with Glass/Polyimide/Indium Tin Oxide for Potentially Flexible Applications

  ACS Applied Energy Materials · 2023-03-23 · 18 citations

  articleCorresponding

  Cu(In,Ga)Se2 (CIGS) is a promising candidate for flexible photovoltaics because of its outstanding efficiency and flexibility. Despite its advantages, achieving high-efficiency CIGS solar cells on a flexible polyimide (PI) substrate is challenging as it requires a low-temperature process and relaxation of the thermal expansion. This limitation is critical in CIGS modules, particularly for monolithic interconnection processes by laser scribing. Furthermore, Mo back-contact (BC)-based PI cells are sensitive to each laser processing step. Laser scribing is one of the important processes in thin-film module manufacturing. In this study, for the first time, we applied indium tin oxide (ITO) instead of Mo as a BC layer on the spin-coated PI on soda-lime glass to obtain mechanically durable CIGS modules. The ITO BC-based module not only provides a crack-free CIGS layer but also offers superior device performance owing to the excellent laser scribing quality. Additionally, electrical properties related to respective scribing steps are analyzed in correlation with observed morphologies to evaluate parasitic resistance and optimize the laser scribing conditions. Consequently, a CIGS monolithic-integrated module with 15.03% efficiency at 40.14 cm2 (16.3% at 0.480 cm2) is fabricated on a novel “soda-lime glass/coated-PI/ITO structure”. We propose ITO BC-based cells as promising candidates for achieving high-efficiency and flexible CIGS solar modules.

  PublisherDOI

• Fabrication of see-through thin film photovoltaic solar cells

  2023-01-01

  article1st authorCorresponding
  PublisherDOI

Frequent coauthors

• Costas P. Grigoropoulos

  University of California, Berkeley

  83 shared

• Seungkuk Kuk

  Samsung (South Korea)

  33 shared

• Robert Horton

  Sandia National Laboratories California

  26 shared

• Sang‐Gil Ryu

  University of California, Berkeley

  25 shared

• Andrew M. Minor

  University of California, Berkeley

  25 shared

• Eunpa Kim

  Samsung (South Korea)

  22 shared

• Jeung‐hyun Jeong

  Korea Institute of Science and Technology

  21 shared

• Nipun Misra

  18 shared

Education

• Ph.D., Mechanical Engineering

  Stony Brook University

  2005

• M.S., Mechanical Engineering

  Stony Brook University

  2002

• B.S., Mechanical Engineering

  Stony Brook University

  2000