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

Simplifying Nanosphere Lithography for Reactive Ion Etch Texturing of Solar Cells

A simplified nanosphere lithography process has been developed which allows fast and low-waste maskings of Si surfaces for subsequent reactive ion etching (RIE) texturing. Initially, a positive surface charge is applied to a wafer surface by dipping in a solution of aluminum nitrate. Dipping the positive-coated wafer into a solution of negatively charged silica beads (nanospheres) results in the spheres becoming electrostatically attracted to the wafer surface. These nanospheres form an etch mask for RIE. After RIE texturing, the reflection of the surface is reduced as effectively as any other nanosphere lithography method, while this batch process used for masking is much faster, making it more industrially relevant

Understanding the impact of carrier mobility and mobile ions on perovskite cell performance

The realization of very high efficiency, stable perovskite solar cells fabricated on a large scale at low cost, has the potential to further lower the cost of photovoltaics. This necessitates an understanding of the properties required of the perovskite material, including the carrier mobility. Perovskite cells also feature mobile ionic species, and the impact of these ions on cell performance- A nd in particular, to what extent and under what circumstances they may limit device performance-is not well understood. Here, we employ an advanced numerical model that allows for the presence of mobile ionic species to probe the relationship between carrier mobility, the presence of ionic species as well as different possible recombination mechanisms within the cell. We show that a high electron and hole conductivity throughout the device is key to avoiding transport losses. For devices operating significantly below their radiative limit, achieving a sufficiently high conductivity requires high carrier mobilities of at least 10cm2/V-s. It is shown that the presence of a single mobile ionic species can lead to effective doping of the perovskite bulk, which is detrimental to cell performance by lowering the conductivity of one type of carrier. The results also indicate that increasing cell VOC closer to its radiative limit is also beneficial for reducing transport losses and pushing cell performance closer to its theoretical limit

A review of thin film crystalline silicon for solar cell applications. Part 1 : native substrates

Approximately half the cost of a furnished crystalline silicon solar module is due to the silicon itself. Combining this fact with a high efficiency potential makes thin film crystalline silicon solar cells a growing research area. This paper, written in two parts, aims to outline world-wide research on this topic. The subject has been divided into techniques which use native substrates and techniques which use foreign substrates. Light trapping, vapour and liquid phase deposition techniques, cell fabrication and some general considerations are also discussed with reference to thin film cells

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

Perovskite Photovoltaic Integrated CdS/TiO2 Photoanode for Unbiased Photoelectrochemical Hydrogen Generation

Photoelectrolysis of water using solar energy into storable and environment-friendly chemical fuel in the form of hydrogen provides a potential solution to address the environmental concerns and fulfill future energy requirements in a sustainable manner. Achieving efficient and spontaneous hydrogen evolution in water using solar light as the only energy input is a highly desirable but a difficult target. In this work, we report perovskite solar cell integrated CdS-based photoanode for unbiased photoelectrochemical hydrogen evolution. An integrated tandem device consisting of mesoporous CdS/TiO2 photoanode paired with a triple-cation perovskite (Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3) solar cell is developed via a facile fabrication route. The proposed photovoltaic integrated photoanode presents an efficient tandem configuration with high optical transparency to long-wavelength photons and strong photoelectrochemical conversions from short-wavelength photons. On the basis of this integrated tandem device, an unbiased photocurrent density of 7.8 mA/cm2 is demonstrated under AM1.5G illumination.ARC grant DP140103278 (2014-2016) - H.H. Tan, Nitride-based Compound Semiconductors for Solar Water Splittin

Superior Self-Powered Room-Temperature Chemical Sensing with Light-Activated Inorganic Halides Perovskites

Hybrid halide perovskite is one of the promising light absorber and is intensively investigated for many optoelectronic applications. Here, the first prototype of a self-powered inorganic halides perovskite for chemical gas sensing at room temperature under visible-light irradiation is presented. These devices consist of porous network of CsPbBr3 (CPB) and can generate an open-circuit voltage of 0.87 V under visible-light irradiation, which can be used to detect various concentrations of O2 and parts per million concentrations of medically relevant volatile organic compounds such as acetone and ethanol with very quick response and recovery time. It is observed that O2 gas can passivate the surface trap sites in CPB and the ambipolar charge transport in the perovskite layer results in a distinct sensing mechanism compared with established semiconductors with symmetric electrical response to both oxidizing and reducing gases. The platform of CPB-based gas sensor provides new insights for the emerging area of wearable sensors for personalized and preventive medicine.H.C. and M.Z. contributed equally to this work. A.T. gratefully acknowledges the support of Australian Research Council (ARC) DP150101939, ARC DE160100569, and Westpac 2016 Research Fellowship. M.Z., S.H., and A.W.Y. H.-B. acknowledge the support of the Australian government via financial support from the ARC through the DP160102955 program and the Australian Renewable Energy Agency. K.R.C. acknowledges the support of an ARC Future Fellowship. The financial support from ARC through DP160102955 is also acknowledged

In situ recombination junction between p-Si and TiO2 enables high-efficiency monolithic perovskite/Si tandem cells

Increasing the power conversion efficiency of silicon (Si) photovoltaics is a key enabler for continued reductions in the cost of solar electricity. Here, we describe a two-terminal perovskite/Si tandem design that increases the Si cell’s output in the simplest possible manner: by placing a perovskite cell directly on top of the Si bottom cell. The advantageous omission of a conventional interlayer eliminates both optical losses and processing steps and is enabled by the low contact resistivity attainable between n-type TiO2 and Si, established here using atomic layer deposition. We fabricated proof-of-concept perovskite/Si tandems on both homojunction and passivating contact heterojunction Si cells to demonstrate the broad applicability of the interlayer-free concept. Stabilized efficiencies of 22.9 and 24.1% were obtained for the homojunction and passivating contact heterojunction tandems, respectively, which could be readily improved by reducing optical losses elsewhere in the device. This work highlights the potential of emerging perovskite photovoltaics to enable low-cost, high-efficiency tandem devices through straightforward integration with commercially relevant Si solar cells