Anh Dinh Bui

To enhance the performance of monolithic perovskite/silicon tandem solar cells toward their theoretical limits and enable commercial‐scale deployment, it is essential to quantify local power losses and identify their physical origins. In this study, we apply a method to extract the local tandem series resistance (LTR _S ), a key contributor to the performance degradation of perovskite/silicon tandem devices. The method is based on bias‐voltage‐dependent photoluminescence (PL) imaging under two different illumination intensities, coupled with the generalized Planck's law. Finite element simulations demonstrate the robustness of the method under a range of realistic conditions, including current mismatch, low shunt resistance, and luminescence coupling effects. When exemplarily applied to a high‐efficiency perovskite/silicon tandem device with a power conversion efficiency PCE of 29%, the method reveals that approximately 1.9% absolute efficiency loss can be attributed to resistive effects. We further investigate the influence of the transient behavior of perovskites on LTR _S measurements using a metastable device. The results show that, even for unstable samples, reliable estimations of LTR _S can be achieved if an appropriate stabilization protocol is employed. These findings establish PL imaging as a powerful diagnostic tool for identifying performance‐limiting regions and guiding the design and processing improvements of next‐generation tandem photovoltaics.

Monolayer molybdenum disulphide (MoS₂) holds great potential for optoelectronic and photovoltaic applications, yet its performance is limited by intrinsic defects, such as sulfur vacancies, that hinder photoluminescence (PL) and charge carrier dynamics. This study investigates the effects of passivation using cation‐based bis(trifluoromethanesulfonimide) (TFSI) treatments (Li‐TFSI, Cs‐TFSI, and Rb‐TFSI) on the optoelectronic properties of MoS₂ monolayers. Implied open‐circuit voltages (iV_oc) at 1 sun illumination are taken from photoluminescence measurements, yielding post‐treatment values of 1425, 1351, and 1381 mV for Li‐TFSI, Rb‐TFSI, and Cs‐TFSI, respectively, indicating reduced non‐radiative recombination. Optical absorption also increased after the cation‐based TFSI treatment, leading to expected improvements in short‐circuit current densities (J_SC). These results demonstrate that cations can play an important role in reducing defect‐related recombination and improving charge carrier dynamics, and that cation‐based TFSI passivation may help to enhance the efficiency of MoS₂‐based optoelectronic devices.

Well‐structured and ordered 2D layered semiconducting materials have excellent optical properties but limited advanced optoelectronic applications in their natural state. Altering their natural arrangement, through artificial heterostructures, strain and pressure engineering, chemical doping, intercalation, and alloying, can impart them with unusual optical properties and potentially enhance their performance in various applications. Among these approaches, alloying is generally difficult to control and disrupts the well‐ordered homophilic crystal phase of these 2D crystals, albeit with the capability to control materials as thin as a single atomic layer. In this work, the synthesis of a low‐dimension ordered–disordered layered 2D alloy of Mo_(1−x)W_xSe₂ with clearly ordered in‐plane segregations of nano‐sized islands of individual MoSe₂ and WSe₂ across the material surface is reported. The optical analysis of this ordered–disordered layered Mo_(1−x)W_xSe₂ reveals unique interfacial and interlayer coupling physics, such as the co‐existence of intralayer (interfacial) and interlayer excitons and enhanced valley polarization of up to 50%, which is traditionally absent in ordered MoSe₂, WSe₂, or their heterostructures. Furthermore, the structure exhibits implies open circuit voltage (up to 1130 mV), signifying its excellent open‐circuit voltage potential if employed in photovoltaic devices. Overall, the reported low‐dimension ordered–disordered semiconductor alloys can be useful in various optoelectronic applications.

Over the past decade, silicon solar cells with carrier‐selective passivating contacts based on polysilicon capping an ultra‐thin silicon oxide (commonly known as TOPCon or POLO) have demonstrated promising efficiency potentials and are regarded as an evolutionary upgrade to the PERC (passivated emitter and rear contact) cells in manufacturing. The polysilicon‐based passivating contacts also exhibit excellent gettering effects that relax the wafer and cleanroom requirements to some extent. In this work, we experimentally explore the impact of bulk iron contamination and polysilicon gettering on the passivation quality of the polysilicon/oxide structure and the resulting solar cells performance. Results show that both n‐ and p‐type polysilicon/oxide passivating contacts are not affected by iron gettering, demonstrating robust and stable passivation quality. However, for a very high bulk iron contamination (1 × 10¹³ cm⁻³), the accumulated iron in the p‐type lightly boron‐doped emitter in crystalline silicon would degrade the emitter saturation current density. This can cause a reduction in both open‐circuit voltage and short‐circuit current. Meanwhile, this very high iron content (1 × 10¹³ cm⁻³) can further degrade the fill factor and temperature coefficient of the cells. On the other hand, for an initial iron content of 2 × 10¹² cm⁻³, which should be well above the iron level in the current industrial Czochralski silicon wafers, the resulting cells demonstrate similar performance as the control group with no intentional iron contamination. This work brings attention to both the benefits of polysilicon gettering effects as well as the potential degradation due to the accumulation of metal impurities in the p‐type emitter region.

Scalable fabrication of all-perovskite tandem solar cells is challenging because the narrow-bandgap subcells made of mixed lead-tin (Pb-Sn) perovskite films suffer from nonuniform crystallization and inferior buried perovskite interfaces. We used a dopant from Good’s list of biochemical buffers, aminoacetamide hydrochloride, to homogenize perovskite crystallization and used it to extend the processing window for blade-coating Pb-Sn perovskite films and to selectively passivate defects at the buried perovskite interface. The resulting all-perovskite tandem solar module exhibited a certified power conversion efficiency of 24.5% with an aperture area of 20.25 square centimeters.

As the efficiency of perovskite silicon tandem solar cells is increasing, the upscaling for industrial production is coming into focus. Spatially resolved, quantitative, fast, and reliable contactless measurement techniques are demanded for quality assurance and to pinpoint the cause of performance losses in perovskite silicon tandem solar cells. In this publication, we present a measurement method based on spectrally integrated photoluminescence (PL) imaging to extract subcell‐selective implied open‐circuit ( ) images from monolithic perovskite silicon tandem solar cells. We validate the approach using spectrally resolved absolute PL measurements based on an integrating sphere for the perovskite top cell and PL‐calibrated carrier lifetime images for the silicon bottom cell. Additionally, measurements of solar cells with low contact losses are used to validate the new measurement technique. We find a good agreement of the images with the validating measurements with a maximum deviation of well below 1% compared to the validation measurements.

As the efficiency of perovskite silicon tandem solar cells is increasing, the upscaling for industrial production is coming into focus. Spatially resolved, quantitative, fast, and reliable contactless measurement techniques are demanded for quality assurance and to pinpoint the cause of performance losses in perovskite silicon tandem solar cells. In this publication we present a measurement method based on spectrally integrated photoluminescence (PL) imaging to extract subcell-selective implied open-circuit ( i V oc ) images from monolithic perovskite silicon tandem solar cells. We validate the approach using spectrally resolved absolute PL measurements based on an integrating sphere for the perovskite top cell and PL-calibrated carrier lifetime images for the silicon bottom cell. Additionally, V oc measurements of solar cells with low contact losses are used to validate the new measurement technique. We find a good agreement of the i V oc images with the validating measurements with a maximum deviation of well below 1 % compared to the validation measurements.

Perovskite solar cells (PSCs) are studied in low-intensity low-temperature (LILT) conditions before and after low energy proton irradiation to characterize device performance at deep space mission-relevant light intensities and temperatures.

Hybrid organic–inorganic perovskite solar cells (PSCs) are one of the most promising candidates for next generation photovoltaics. Further improvement in their performance, particularly efficiency, durability and reproducibility, requires a deep understanding of recombination losses during fabrication and within a device itself. In this work, we report a contactless, imaging‐based procedure to spatially resolve electronic properties of PSCs including implied open‐circuit voltage (iV_oc) and its temperature coefficient, ideality factor (n_id) and activation energy of recombination (E_A) by employing illumination intensity and temperature‐dependent photoluminescence. The illumination intensity dependence of iV_oc allows the extraction of n_id whereas its temperature dependence allows the extraction of the temperature coefficient and E_A. This imaging approach is then applied to investigate changes of these electronic parameters on fully and partially fabricated devices.