Plasmon-enhanced internal photoemission for photovoltaics: Theoretical efficiency limits

Plasmon-enhanced internal photoemission in metal-semiconductor Schottky junctions has recently been proposed as an alternative photocurrent mechanism for solar cells. Here, we identify and discuss the requirements for efficient operation of such cells and analyze their performance limits under standard solar illumination. We show that the maximum efficiency limit is 20%.We acknowledge the Australian Research Council and the Australian Solar Institute for financial support

Effective light trapping in polycrystalline silicon thin-film solar cells by means of rear localized surface plasmons

Significant photocurrent enhancement has been achieved for evaporated solid-phase-crystallized polycrystalline siliconthin-filmsolar cells on glass, due to light trapping provided by Agnanoparticles located on the rear siliconsurface of the cells. This configuration takes advantage of the high scattering cross-section and coupling efficiency of rear-located particles formed directly on the optically dense silicon layer. We report short-circuit current enhancement of 29% due to Agnanoparticles, increasing to 38% when combined with a detached back surface reflector. Compared to conventional light trapping schemes for these cells, this method achieves 1/3 higher short-circuit current

The Two Faces of Capacitance: New Interpretations for Electrical Impedance Measurements of Perovskite Solar Cells and Their Relation to Hysteresis

Perovskite solar cells are notorious for exhibiting transient behaviour not seen in conventional inorganic semiconductor devices. Significant inroads have been made into understanding this fact in terms of rapid ion migration, now a well-established property of the prototype photovoltaic perovskite MAPbI$_3$ and strongly implicated in the newer mixed compositions. Here we study the manifestations of ion migration in frequency-domain small-signal measurements, focusing on the popular technique of Electrical Impedance Spectroscopy (EIS). We provide new interpretations for a variety of previously puzzling features, including giant photo-induced low-frequency capacitance and negative capacitance in a variety of forms. We show that these apparently strange measurements can be rationalized by the splitting of AC current into two components, one associated with charge-storage, and the other with the quasi-steady-state recombination current of electrons and holes. The latter contribution to the capacitance can take either a positive or a negative sign, and is potentially very large when slow, voltage-sensitive processes such as ion migration are at play. Using numerical drift-diffusion semiconductor models, we show that giant photo-induced capacitance, inductive loop features, and low-frequency negative capacitance all emerge naturally as consequences of ion migration via its coupling to quasi-steady-state electron and hole currents. In doing so, we unify the understanding of EIS measurements with the comparably well-developed theory of rate dependent current-voltage (I-V) measurements in perovskite cells. Comparing the two techniques, we argue that EIS is more suitable for quantifying I-V hysteresis than conventional methods based on I-V sweeps, and demonstrate this application on a variety of cell types.Comment: Fixed typos and amended the axes on Figure 3 for clarit

Highly Reflective Dielectric Back Reflector for Improved Efficiency of Tandem Thin-Film Solar Cells

We report on the prototyping and development of a highly reflective dielectric back reflector for application in thin-film solar cells. The back reflector is fabricated by Snow Globe Coating (SGC), an innovative, simple, and cheap process to deposit a uniform layer of TiO2 particles which shows remarkably high reflectance over a broad spectrum (average reflectance of 99% from 500 nm to 1100 nm). We apply the highly reflective back reflector to tandem thin-film silicon solar cells and compare its performance with conventional ZnO:Al/Ag reflector. By using SGC back reflector, an enhancement of 0.5 mA/cm2 in external quantum efficiency of the bottom solar cell and an absolute value of 0.2% enhancement in overall power conversion efficiency are achieved. We also show that the increase in power conversion efficiency is due to the reduction of parasitic absorption at the back contact; that is, the use of the dielectric reflector avoids plasmonic losses at the reference ZnO:Al/Ag back reflector. The Snow Globe Coating process is compatible with other types of solar cells such as crystalline silicon, III–V, and organic photovoltaics. Due to its cost effectiveness, stability, and excellent reflectivity above a wavelength of 400 nm, it has high potential to be applied in industry

Device Performance of Emerging Photovoltaic Materials (Version 2)

Following the 1st release of the “Emerging photovoltaic (PV) reports”, the best achievements in the performance of emerging photovoltaic devices in diverse emerging photovoltaic research subjects are summarized, as reported in peer-reviewed articles in academic journals since August 2020. Updated graphs, tables, and analyses are provided with several performance parameters, e.g., power conversion efficiency, open-circuit voltage, short-circuit current density, fill factor, light utilization efficiency, and stability test energy yield. These parameters are presented as a function of the photovoltaic bandgap energy and the average visible transmittance for each technology and application and are put into perspective using, e.g., the detailed balance efficiency limit. The 2nd instalment of the “Emerging PV reports” extends the scope toward tandem solar cells and presents the current state-of-the-art in tandem solar cell performance for various material combinations.</p

Device Performance of Emerging Photovoltaic Materials (Version 1)

Emerging photovoltaics (PVs) focus on a variety of applications complementing large scale electricity generation. Organic, dye‐sensitized, and some perovskite solar cells are considered in building integration, greenhouses, wearable, and indoor applications, thereby motivating research on flexible, transparent, semitransparent, and multi‐junction PVs. Nevertheless, it can be very time consuming to find or develop an up‐to‐date overview of the state‐of‐the‐art performance for these systems and applications. Two important resources for recording research cells efficiencies are the National Renewable Energy Laboratory chart and the efficiency tables compiled biannually by Martin Green and colleagues. Both publications provide an effective coverage over the established technologies, bridging research and industry. An alternative approach is proposed here summarizing the best reports in the diverse research subjects for emerging PVs. Best performance parameters are provided as a function of the photovoltaic bandgap energy for each technology and application, and are put into perspective using, e.g., the Shockley–Queisser limit. In all cases, the reported data correspond to published and/or properly described certified results, with enough details provided for prospective data reproduction. Additionally, the stability test energy yield is included as an analysis parameter among state‐of‐the‐art emerging PVs

Diffuse reflectors for improving light management in solar cells: a review and outlook

Pigment based diffuse reflectors (DRs) have several advantages over metal reflectors such as good stability, high reflectivity, and low parasitic absorption. As such, DRs have the potential to be applied on high efficiency silicon solar cells and further increase the power conversion efficiency. In this paper, we perform a thorough review on the notable achievements to date of DRs’ application for photovoltaics. We outline unique attributes of these technologies and discuss the theoretical and laboratory development working towards overcoming the challenges of transferring to high efficiency silicon solar cells. In order to understand the potential of DRs for high efficiency silicon solar cells, we provide a qualitative analysis of the impact of front reflection, rear absorption and the angular distribution on the useful light absorption in silicon wafers. By including this discussion, we provide an outlook for the application of DR in reaching maximum photo-current for high efficiency silicon solar cells

Light trapping with plasmonic particles: beyond the dipole model

Disk-shaped metal nanoparticles on high-index substrates can support resonant surface plasmon polariton (SPP) modes at the interface between the particle and the substrate. We demonstrate that this new conceptual model of nanoparticle scattering allows clear predictive abilities, beyond the dipole model. As would be expected from the nature of the mode, the SPP resonance is very sensitive to the area in contact with the substrate, and insensitive to particle height. We can employ this new understanding to minimise mode out-coupling and Ohmic losses in the particles. Taking into account optical losses due to parasitic absorption and outcoupling of scattered light, we estimate that an optimal array of nanoparticles on a 2 μm Si substrate can provide up to 71% of the enhancement in absorption achievable with an ideal Lambertian rear-reflector. This result compares to an estimate of 67% for conventional pyramid-type light trapping schemes