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In photovoltaic (PV) materials development, the complex relationship between device performance and underlying materials parameters obfuscates experimental feedback from current-voltage (J-V) characteristics alone. Here, we address this complexity by adding temperature and injection dependence and applying a Bayesian inference approach to extract multiple device-relevant materials parameters simultaneously. Our approach is an order of magnitude faster than the cumulative time of multiple individual spectroscopy techniques, with added advantages of using device-relevant materials stacks and interface conditions. We posit that this approach could be broadly applied to other semiconductor- and energy-device problems of similar complexity, accelerating the pace of experimental research. Photovoltaic (PV) research has historically taken decades to bring new materials to market, as the pace of development is often limited by our ability to identify the causes of underperformance. There are many ways to make an underperforming PV cell, and their signatures on device efficiency alone are not unique. This uncertainty plagues other energy-storage or -conversion devices with similarly complex combinations of materials but may be used to our advantage. By probing or biasing a PV cell in different operating conditions, the signature of underlying material properties becomes more unique. This connection between the operating conditions, the material properties, and the PV cell output may be solved through Bayesian inference algorithms. While computationally expensive, high-performance computing can enable such inference as a tool for experimentalists, a tool that could become increasingly valuable for accelerating the pace of materials research in PV and related fields. High-performance computing can greatly improve the workflow of experimentalists in energy materials, through the use of Bayesian inference. This allows us to solve the inverse problem of extracting underlying materials properties through the measurement of the electrical behavior of completed devices. Cheaper, faster measurements can be substituted for longer direct measurements of individual properties, without sacrificing accuracy or precision. We provide a general framework to apply this to other materials systems and devices.

To experimentally identify the character of radiative transitions in trigonal Cu2BaSnS4, we conduct temperature and excitation intensity dependent photoluminescence (PL) measurements in the temperature range of 15–300 K. The low-temperature near band edge PL spectrum is interpreted as the free exciton at 2.11 eV and the bound exciton at 2.08 eV, coupled with associated phonon-assisted transitions. In the low energy region, we assign the dominant defect emission at 1.96 eV to donor–acceptor-pair recombination and the weak broad emission at 1.6 eV to the free-to-bound transition. The activation energies and temperature shift for the radiative transitions are determined and discussed. Above 90 K, the free exciton recombination becomes the dominant radiative transition, with its energy shift mainly governed by the contribution of optical phonons. [ABSTRACT FROM AUTHOR]

The depth distribution of secondary phases in the solar cell absorber material Cu2ZnSnS4 (CZTS) is quantitatively investigated using X-ray Absorption Near Edge Structure (XANES) analysis at the K-edge of sulfur at varying incidence angles. Varying information depths from several nanometers up to the full thickness is achieved. A quantitative profile of the phase distribution is obtained by a self-consistent fit of a multilayer model to the XANES spectra for different angles. Single step coevaporated CZTS thin-films are found to exhibit zinc and copper sulfide secondary phases preferentially at the front or back interfaces of the film. [ABSTRACT FROM AUTHOR]

Distinguishing among different electrical loss mechanisms − such as interface and bulk recombination − is a common problem in thin film solar cells. In this work, we report a J–V measurement technique using different illuminating spectra to distinguish between these two recombination losses. The basic idea is to change the relative contribution of bulk recombination to the total losses of photo-generated charge carriers by generating them in different depths within the absorber layer using different spectral regions of the illuminating light. The use of modern LED sun-simulators allows an almost free design of illumination spectra at intensities close to 1 sun. The comparison of two simple J–V measurements, one recorded with illumination near the absorber's band-gap energy and one with light of higher energy, in combination with supporting measurements of the absorber properties, as well as device modeling, enables the extraction of the diffusion length and the interface recombination velocity. Using this technique, we show that in CIGS solar cells, an RbF post-deposition treatment does not only reduce interface recombination losses, as often reported, but also reduces bulk recombination in the CIGS absorber. Furthermore, we find that both cells, with and without RbF treatment, are dominantly affected by interface recombination losses.

Phase segregation in inorganic CsPb(Br x I 1- x ) 3 nanoparticles (NPs) exhibiting originally a homogeneous [Br]:[I] mixture was investigated by means of in situ transmission electron microscopy (TEM) and evaluated by using multivariate analyses. The colloidal synthesis of the NPs offers good control of the halide ratios on the nanoscale. The spatially resolved TEM investigations were correlated with integral photoluminescence measurements. By this approach, the halide-segregation processes and their spatial distributions can be described as being governed by the interaction of three partial processes: electron- and photon-irradiation-induced iodide oxidation, local differences in band gap energy, and intrinsic lattice strain. Since the oxidation can be induced by both electron-beam and light irradiation, both irradiation types can induce phase segregation in CsPb(Br x I 1- x ) 3 compounds. This makes in situ TEM a valuable tool to monitor phase transformation in corresponding NPs and thin films on the sub-nm scale., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Halide perovskite-based photon upconverters utilize perovskite thin films to sensitize triplet exciton formation in a small-molecule layer, driving triplet-triplet annihilation upconversion. Despite having excellent carrier mobility, these systems suffer from inefficient triplet formation at the perovskite/annihilator interface. We studied triplet formation in formamidinium-methylammonium lead iodide/rubrene bilayers using photoluminescence and surface photovoltage methods. By studying systems constructed on glass as well as hole-selective substrates, comprising self-assembled layers of the carbazole derivative 2PACz ([2-(9H-carbazol-9-yl)ethyl]phosphonic acid) on indium-doped tin oxide, we saw how changes in the carrier dynamics induced by the hole-selective substrate perturbed triplet formation at the perovskite/rubrene interface. We propose that an internal electric field, caused by hole transfer at the perovskite/rubrene interface, strongly affects triplet exciton formation, accelerating exciton-forming electron-hole encounters at the interface but also limiting the hole density in rubrene at high excitation densities. Controlling this field is a promising path to improving triplet formation in perovskite/annihilator upconverters., Competing Interests: The authors declare no competing interests., (© 2023 The Author(s).)

I-V-VI 2 ternary chalcogenides are gaining attention as earth-abundant, nontoxic, and air-stable absorbers for photovoltaic applications. However, the semiconductors explored thus far have slowly-rising absorption onsets, and their charge-carrier transport is not well understood yet. Herein, we investigate cation-disordered NaBiS 2 nanocrystals, which have a steep absorption onset, with absorption coefficients reaching >10 5  cm -1 just above its pseudo-direct bandgap of 1.4 eV. Surprisingly, we also observe an ultrafast (picosecond-time scale) photoconductivity decay and long-lived charge-carrier population persisting for over one microsecond in NaBiS 2 nanocrystals. These unusual features arise because of the localised, non-bonding S p character of the upper valence band, which leads to a high density of electronic states at the band edges, ultrafast localisation of spatially-separated electrons and holes, as well as the slow decay of trapped holes. This work reveals the critical role of cation disorder in these systems on both absorption characteristics and charge-carrier kinetics., (© 2022. The Author(s).)

Phosphides are interesting candidates for hole transport materials and p-type transparent conducting applications, capable of achieving greater valence band dispersion than their oxide counterparts due to the higher lying energy and increased size of the P 3p orbital. After computational identification of the indirect-gap semiconductor CaCuP as a promising candidate, we now report reactive sputter deposition of phase-pure p-type CaCuP thin films. Their intrinsic hole concentration and hole mobility exceed 1 × 10 20 cm -3 and 35 cm 2 V -1 s -1 at room temperature, respectively. Transport calculations indicate potential for even higher mobilities. Copper vacancies are identified as the main source of conductivity, displaying markedly different behaviour compared to typical p-type transparent conductors, leading to improved electronic properties. The optical transparency of CaCuP films is lower than expected from first principles calculations of phonon-mediated indirect transitions. This discrepancy could be partly attributed to crystalline imperfections within the films, increasing the strength of indirect transitions. We determine the transparent conductor figure of merit of CaCuP films as a function of composition, revealing links between stoichiometry, crystalline quality, and opto-electronic properties. These findings provide a promising initial assessment of the viability of CaCuP as a p-type transparent contact., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Background: Eliminating the NIH funding gap among underrepresented minorities (URMs) remains a high priority for the National Institutes of Health. In 2014, the National Research Mentoring Network 1 Steps Toward Academic Research (NRMN STAR) program recruited postdoctoral, early-stage and junior faculty to participate in a 12-month grant writing and professional development program. The expectation of the program was to increase the number of grant submissions and awards to URM researchers. Although receiving a grant award is the gold standard of NRMN STAR, instilling confidence for postdocs and early-stage faculty to submit an application is a critical first step. Based on our previous study, a sustained increase in trainee self-efficacy score over a 24-month period was observed after completing NRMN STAR., Methods: The current study sought to determine the association between self-efficacy score and grant submissions among two cohorts of trainees. Grantsmanship Self-Efficacy was measured using a 19-item questionnaire previously described by and used in our own work, which was originally adapted from an 88-item Clinical Research Appraisal Inventory. 2 A binary variable was created to identify trainees who submitted an initial or revised proposal vs those who abandoned their proposal or were still writing. Trainees were assessed prior to and following program completion with subsequent assessments at 6 and 12 months beyond participation., Results: As of June 20, 2019, 12 of the 21 (57%) trainees had submitted a grant proposal (eg, NIH, other federal or non-federal grant). For every point increase in 12-month post assessments, Grantsmanship Self-Efficacy scores across all domains had a 44% higher prevalence of submitting a grant after controlling for race, sex, education level, academic rank, research experience, duration of postdoctoral training, institution type, and NRMN STAR cohort., Conclusions: Our findings demonstrate that NRMN STAR had a positive impact on trainees' confidence in grant writing and professional development activities, which resulted in higher grant submission rates., Competing Interests: Competing Interests: None declared., (Copyright © 2021, Ethnicity & Disease, Inc.)

Background: A diverse research workforce is essential for catalyzing biomedical advancements, but this workforce goal is hindered by persistent sex and racial/ethnic disparities among investigators receiving research grants from the National Institutes of Health (NIH). In response, the NIH-funded National Research Mentoring Network implemented a Grant Writing Coaching Program (GCP) to provide diverse cohorts of early-career investigators across the United States with intensive coaching throughout the proposal development process. We evaluated the GCP's national reach and short-term impact on participants' proposal submissions and funding outcomes., Methods: The GCP was delivered as six similar but distinct models. All models began with an in-person group session, followed by a series of coaching sessions over 4 to 12 months. Participants were surveyed at 6-, 12- and 18-months after program completion to assess proposal outcomes (submissions, awards). Self-reported data were verified and supplemented by searches of public repositories of awarded grants when available. Submission and award rates were derived from counts of participants who submitted or were awarded at least one grant proposal in a category (NIH, other federal, non-federal)., Results: From June 2015 through March 2019, 545 investigators (67% female, 61% under-represented racial/ethnic minority, URM) from 187 different institutions participated in the GCP. Among them, 324 (59% of participants) submitted at least one grant application and 134 (41% of submitters) received funding. A total of 164 grants were awarded, the majority being from the NIH (93, 56%). Of the 74 R01 (or similar) NIH research proposals submitted by GCP participants, 16 have been funded thus far (56% to URM, 75% to women). This 22% award rate exceeded the 2016-2018 NIH success rates for new R01s., Conclusion: Inter- and intra-institutional grant writing coaching groups are a feasible and effective approach to supporting the grant acquisition efforts of early-career biomedical investigators, including women and those from URM groups., Competing Interests: The authors have declared that no competing interests exist.

Thin-film solar cells based on polycrystalline absorbers have reached very high conversion efficiencies of up to 23-25%. In order to elucidate the limiting factors that need to be overcome for even higher efficiency levels, it is essential to investigate microscopic origins of loss mechanisms in these devices. In the present work, a high efficiency (21% without anti-reflection coating) copper indium gallium diselenide (CIGSe) solar cell is characterized by means of a correlative microscopy approach and corroborated by means of photoluminescence spectroscopy. The values obtained by the experimental characterization are used as input parameters for two-dimensional device simulations, for which a real microstructure was used. It can be shown that electrostatic potential and lifetime fluctuations exhibit no substantial impact on the device performance. In contrast, nonradiative recombination at random grain boundaries can be identified as a significant loss mechanism for CIGSe solar cells, even for devices at a very high performance level.

The NRMN STAR program was created to address the persistent underrepresentation in grant submissions and receipt of National Institutes of Health (NIH) awards by racial/ethnic minority groups. In our current study, we assessed program impact on trainees' self-efficacy related to grant writing. The program was conducted with two cohorts: one in June 2014 and one in June 2015. We used a 19-item grant writing self-efficacy scale drawn from the 88-item Clinical Research Assessment Inventory of three domains (conceptualizing, designing, and funding a study) to predict whether self-efficacy influences researchers' grant submissions. Trainees were assessed prior to and following program completion with subsequent assessments at 6 and 12 months beyond participation. The majority of trainees were Black (62%), female (62%), and had obtained a PhD (90%). More than half (52%) were assistant professors and 57% had none or <1 year of research experience beyond postdoctoral training. However, 24% of trainees reported no postdoctoral research training. NRMN STAR trainees' self-efficacy significantly improved on all three domains exhibiting a 2.0-point mean change score on two domains (conceptualizing and design) and 3.7 point mean change score on the domain, funding a study. Findings suggest that NRMN's STAR provides impactful, confidence-building training for diverse, early stage investigators with little-to-no skills, experiences, or low self-efficacy in writing research grants., Competing Interests: Competing Interests: None declared., (Copyright © 2020, Ethnicity & Disease, Inc.)

By using synchrotron X-ray powder diffraction, the temperature dependent phase diagram of the hybrid perovskite tri-halide compounds, methyl ammonium lead iodide (MAPbI 3 , MA + = CH 3 NH 3 + ) and methyl ammonium lead bromide (MAPbBr 3 ), as well as of their solid solutions, has been established. The existence of a large miscibility gap between 0.29 ≤ x ≤ 0.92 (±0.02) for the MAPb(I 1- x Br x ) 3 solid solution has been proven. A systematic study of the lattice parameters for the solid solution series at room temperature revealed distinct deviations from Vegard's law. Furthermore, temperature dependent measurements showed that a strong temperature dependency of lattice parameters from the composition is present for iodine rich compositions. In contrast, the bromine rich compositions show an unusually low dependency of the phase transition temperature from the degree of substitution., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The mobilities of electrons and holes determine the applicability of any semiconductor, but their individual measurement remains a major challenge. Here, we show that time-resolved terahertz spectroscopy (TRTS) can distinguish the mobilities of minority and majority charge carriers independently of the doping-type and without electrical contacts. To this end, we combine the well-established determination of the sum of electron and hole mobilities from photo-induced THz absorption spectra with mobility-dependent ambipolar modeling of TRTS transients. The method is demonstrated on a polycrystalline Cu 2 ZnSnSe 4 thin film and reveals a minority (electron) mobility of 128 cm 2 /V-s and a majority (hole) carrier mobility of 7 cm 2 /V-s in the vertical transport direction relevant for light emitting, photovoltaic and solar water splitting devices. Additionally, the TRTS analysis yields an effective bulk carrier lifetime of 4.4 ns, a surface recombination velocity of 6 * 10 4  cm/s and a doping concentration of ca. 10 16 cm -3 , thus offering the potential for contactless screen novel optoelectronic materials.

Kelvin Probe Force Microscopy, Photoluminescence imaging and numerical simulations are used to study the surfaces of Cu 2 ZnSnSe 4 absorber layers. In particular, the effect of NH 4 OH and annealing under ambient conditions is investigated. We observe drastic changes in the measured quasi Fermi-level splitting (QFLs) after chemical cleaning of the absorber surface with NH 4 OH, which is traced back to a removal of the surface inversion. Air annealing recovers surface inversion, which reduces the recombination current at the surface. Annealing above 200 °C leads to a permanent change in the work function which cannot be modified by NH 4 OH etching anymore. This modification makes the QFLs insensitive to surface cleaning and explains why air annealing in Cu 2 ZnSnSe 4 is important. From numerical simulations we find that a large surface recombination velocity needs to be present in order to describe the experimental observations.

Background and Purpose: Effective mentorship is critical to the success of early stage investigators, and has been linked to enhanced mentee productivity, self-efficacy, and career satisfaction. The mission of the National Research Mentoring Network (NRMN) is to provide all trainees across the biomedical, behavioral, clinical, and social sciences with evidence-based mentorship and professional development programming that emphasizes the benefits and challenges of diversity, inclusivity, and culture within mentoring relationships, and more broadly the research workforce. The purpose of this paper is to describe the structure and activities of NRMN., Key Highlights: NRMN serves as a national training hub for mentors and mentees striving to improve their relationships by better aligning expectations, promoting professional development, maintaining effective communication, addressing equity and inclusion, assessing understanding, fostering independence, and cultivating ethical behavior. Training is offered in-person at institutions, regional training, or national meetings, as well as via synchronous and asynchronous platforms; the growing training demand is being met by a cadre of NRMN Master Facilitators. NRMN offers career stage-focused coaching models for grant writing, and other professional development programs. NRMN partners with diverse stakeholders from the NIH-sponsored Diversity Program Consortium (DPC), as well as organizations outside the DPC to work synergistically towards common diversity goals. NRMN offers a virtual portal to the Network and all NRMN program offerings for mentees and mentors across career development stages. NRMNet provides access to a wide array of mentoring experiences and resources including MyNRMN, Guided Virtual Mentorship Program, news, training calendar, videos, and workshops. National scale and sustainability are being addressed by NRMN "Coaches-in-Training" offerings for more senior researchers to implement coaching models across the nation. "Shark Tanks" provide intensive review and coaching for early career health disparities investigators, focusing on grant writing for graduate students, postdoctoral trainees, and junior faculty., Implications: Partners from diverse perspectives are building the national capacity and sparking the institutional changes necessary to truly diversify and transform the biomedical research workforce. NRMN works to leverage resources towards the goals of sustainability, scalability, and expanded reach., Competing Interests: Not applicable.Not applicable.The authors declare that they have no competing interests.Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

The influence of structure geometry on THz emission from Black Silicon (BS) surfaces fabricated by reactive ion etching (RIE) has been investigated by a comprehensive study including optical simulations, optical-pump THz probe and THz emission studies. A strong enhancement of THz emission is observed with increasing structure depth, which is mainly related to the increased number of carriers created within the silicon needles and not due to the overall absorption enhancement as previously claimed for silicon nanowires.