Despite the exceeding 23\% photovoltaic efficiency achieved in organic-inorganic hybrid perovskite solar cells obtaining, the stable materials with desirable band gap are rare and are highly desired. With the aid of first-principles calculations, we predict a new promising family of nontoxic inorganic double perovskites (DPs), namely, silicon (Si)-based halides A$_{2}$SiI$_{6}$ (A = K, Rb, Cs; X = Cl, Br, I). This family containing the earth-abundant Si could be applied for perovskite solar cells (PSCs). Particularly A$_{2}$SiI$_{6}$ exhibits superb physical traits, including suitable band gaps of 0.84-1.15 eV, dispersive lower conduction bands, small carrier effective masses, wide photon absorption in the visible range. Importantly, the good stability at high temperature renders them as promising optical absorbers for solar cells.
In this article, the stability of p-i-n perovskite solar cells is studied under accelerated heat lifetime conditions (60 oC ,85oC and N2 atmosphere). By using a combination of buffer layer engineering, impedance spectroscopy and other characterization techniques, we propose the interaction of the perovskite active layer with the top Al metal electrode through diffusion mechanisms as the major thermal degradation pathway for planar inverted perovskite photovoltaics (PVs) under 85oC heat conditions. We show that by using thick solution processed fullerene buffer layer the perovskite active layer…
Halide perovskites have outstanding photovoltaic properties which have been optimized through interfacial engineering. However, as these materials approach the limits imposed by the physics of semiconductor junctions, it is urgent to explore alternatives, such as the bulk photovoltaic effect, whose physical origin is different and not bound by the same limits. In this context, we focus on the flexo-photovoltaic effect, a type of bulk photovoltaic effect that was recently observed in oxides under strain gradients. We have measured the flexo-photovoltaic effect of MAPbBr3 and MAPbI3 crystals und…
Lead-halide perovskites have demonstrated astonishing increases in power conversion efficiency in photovoltaics over the last decade. The most efficient perovskite devices now outperform industry-standard multi-crystalline silicon solar cells, despite the fact that perovskites are typically grown at low temperature using simple solution-based methods. However, the toxicity of lead and its ready solubility in water are concerns for widespread implementation. These challenges, alongside the many successes of the perovskites, have motivated significant efforts across multiple disciplines to find …
Solution processed γ-Fe2O3 nanoparticles via the solvothermal colloidal synthesis in conjunction with ligand-exchange method are used for interface modification of the top electrode in inverted perovskite solar cells. In comparison to more conventional top electrodes such as PC(70)BM/Al and PC(70)BM/AZO/Al, we show that incorporation of a γ-Fe2O3 provides an alternative solution processed top electrode (PC(70)BM/γ-Fe2O3/Al) that not only results in comparable power conversion efficiencies but also improved thermal stability of inverted perovskite photovoltaics. The origin of improved stability…
Perovskite solar cells (PSCs) with superior performance have been recognized as a potential candidate in photovoltaic technologies. However, the defects in active perovskite layer induce non-radiative recombination which restricts the performance and stability of the PSCs. The construction of thiophene-based 2D structure is one of the significant approaches for surface passivation of hybrid PSCs that may combine the benefits of the stability of 2D perovskite with the high performance of 3D perovskite. Here, a sulfur-rich spacer cation 2-thiopheneethylamine iodide (TEAI) is synthesized as a pas…
With the rapid progress of perovskite photovoltaics (PV), further challenges arise to meet meet the minimum standards required for commercial deployment. Along with the push towards higher efficiencies, we identify a need to improve the quality and uniformity of reported research data and to focus efforts upon understanding and overcoming failures during operation. In this perspective, as a large and representative consortium of researchers active in this field, we discuss which methods require special attention and issue a series of recommendations to improve research practices and reporting.
Methyl-ammonium lead iodide perovskite crystallizes in different structures depending on the temperature: orthorhombic, tetragonal and cubic. An important point to be considered is the effect of the microscopic properties of the different structures on the optical and photovoltaic properties. Using first principles we obtain the absorption coefficients that will determine the absorption of solar radiation. In order to analyze the contributions of the different atoms to the absorption coefficients we split them into a many-species expansion. Using a similar methodology we also split the efficie…
Metal halide perovskites feature excellent absorption, emission and charge carrier transport properties. These materials are therefore very well suited for photovoltaics applications where there is a growing interest. Still, questions arise when looking at the unusual long carrier lifetime that, regarding the micrometric diffusion length, would imply a very low diffusion coefficient as compared to commonly used photovoltaic absorbers. In this paper, we provide an experimental insight into this long lifetime of charge carriers in slow-motion. Our approach relies on an improved model to analyze …
Organic-inorganic lead halide perovskites containing a mixture of iodide and bromide anions consistently perform better in donor-acceptor heterojunction solar cells than the standard methylammonium lead triiodide material. This observation is counterintuitive, as it is generally expected for photovoltaic materials that heterogeneities and compositional disorder cause reduced carrier diffusion length and conversion efficiency. Here, we combine ultrafast photoinduced electroabsorption and broadband fluorescence up-conversion spectroscopy measurements to scrutinize the carrier dynamics in mixed-c…
Singlet fission process has gained considerable attention because of its potential to enhance photovoltaic efficiency and break the Shockley Queisser limit. In photovoltaic devices perovskite materials have shown tremendous progress in the last decade. Therefore combining the singlet fission materials in perovskite devices can lead to a drastic enhancement in their performance. To reveal the applicability of singlet fission processes in perovskite materials we have investigated the charge transfer dynamics from an SF active material 910 bis phenylethynyl anthracene to CH3NH3PbBr3 perovskite na…
Light Management (LM) is essential for metal-halide perovskite solar cells in their race for record performance. In this review, criteria on materials, processes and photonic engineering are established such as to enhance mainly the short circuit current density, towards high energy yields. These criteria are used to analyse a large panel of solutions envisaged in the literature for single junction cells. Moreover, a perspective based on rigorous electromagnetic simulations performed on various comparable structures is proposed in order to clarify the conclusions, and to pave the way to furthe…
Indoor photovoltaics are receiving tremendous attention due to the continuous development of the Internet of Things (IoT). Here we report a triple anion (TA) perovskite CH3NH3PbI2.6(BrCl)0.2 with a tailored bandgap suitable for maximizing indoor light harvesting compared to methyl ammonium lead iodide CH3NH3PbI3. The best-performing TA perovskite indoor-photovoltaic device achieved a steady-state power conversion efficiency (PCE) of 25.1% with an output power density of ~ 75 microW/cm2 under 1000 lux indoor illumination (0.3 mW/cm2 irradiance). This PCE is almost 40% higher than that of equiva…
Perovskite solar cell (PSC) is one of the most promising next generation photovoltaic technologies, and there are considerable interests in the role of possible polarization of organic-inorganic halide perovskites (OIHPs) in photovoltaic conversion. The polarity of OIHPs, however, is still hotly debated. In this review, we examine recent literature on the polarity of OIHPs from both theoretical and experimental points of view, and argue that they can be both polar and nonpolar, depending on compositions, processing, and environments. Implications of OIHP polarity to photovoltaic conversion is …
The previously developed bistable amphoteric native defect (BAND) model is used for a comprehensive explanation of the unique photophysical properties and for understanding the remarkable performance of perovskites as photovoltaic materials. It is shown that the amphoteric defects in donor (acceptor) configuration capture a fraction of photoexcited electrons (holes) dividing them into two groups: higher energy bright and lower energy dark electrons (holes). The spatial separation of the dark electrons and the dark holes and the k-space separation of the bright and the dark charge carriers redu…
The last five years have witnessed a remarkable progress in the field of lead halide perovskite materials and devices. Examining the existing body of literature reveals staggering inconsistencies in the reported results among different research groups with a particularly wide spread in the photovoltaic performance and stability of devices. In this work we demonstrate that fractional, quite possibly unintentional, deviations in the precursor solution stoichiometry can cause significant changes in the properties of the perovskite layer as well as in the performance and stability of perovskite ph…
In this perspective, we explore the insights into the device physics of perovskite solar cells gained from modeling and simulation of these devices. We discuss a range of factors that influence the modeling of perovskite solar cells, including the role of ions, dielectric constant, density of states, and spatial distribution of recombination losses. By focusing on the effect of non-ideal energetic alignment in perovskite photovoltaic devices, we demonstrate a unique feature in low recombination perovskite materials - the formation of an interfacial, primarily electronic, self-induced dipole th…
We present the functionalization process of a conductive and transparent copper aluminum oxide, copper oxide alloy. The copper aluminum oxide, copper oxide powders were developed by flame spray pyrolysis and their stabilized dispersions were treated by sonication and centrifugation methods. We show that when the supernatant part of the treated copper aluminum oxide, copper oxide dispersions is used for the development of hole transporting layers the corresponding inverted perovskite solar cells show improved functionality and power conversion efficiency with negligible hysteresis effect.
Most traditional semiconductor materials are based on the control of doping densities to create junctions and thereby functional and efficient electronic and optoelectronic devices. The technology development for halide perovskites had initially only rarely made use of the concept of electronic doping of the perovskite layer and instead employed a variety of different contact materials to create functionality. Only recently, intentional, or unintentional doping of the perovskite layer is more frequently invoked as an important factor explaining differences in photovoltaic or optoelectronic per…
All-perovskite tandem solar cells promise high photovoltaic performance at low cost. So far however, their efficiencies cannot compete with traditional inorganic multi-junction solar cells and they generally underperform in comparison to what is expected from the isolated single junction devices. Understanding performance losses in all-perovskite tandem solar cells is a crucial aspect that will accelerate advancement. Here, we perform extensive selective characterization of the individual sub-cells to disentangle the different losses and limiting factors in these tandem devices. We find that n…
Solution combustion synthesized hole transport layer of co-doped spinel nickel cobaltite were fabricated using doctor-blading technique for planar inverted perovskite solar cells. Perovskite solar cells incorporating Co-doped spinel nickel cobaltite shown an increase in device performance parameters compared to un-doped spinel nickel cobaltite, leading to PCE of 16.5%. X-ray photoelectron spectroscopy measurements revealed the tendency of Cu cations to replace preferably the surface Ni atoms changing the surface stoichiometry of spinel nickel cobaltite inducing a cathodic polarization. Ultravi…
We present a new approach to ubiquitous sensing for indoor applications, using high-efficiency and low-cost indoor perovksite photovoltaic cells as external power sources for backscatter sensors. We demonstrate wide-bandgap perovskite photovoltaic cells for indoor light energy harvesting with the 1.63eV and 1.84 eV devices demonstrate efficiencies of 21% and 18.5% respectively under indoor compact fluorescent lighting, with a champion open-circuit voltage of 0.95 V in a 1.84 eV cell under a light intensity of 0.16 mW/cm2. Subsequently, we demonstrate a wireless temperature sensor self-powered …
Optimizing selective contact layers in photovoltaics is necessary to yield high performing stable devices. However, this has been difficult for perovskites due to their complex interfacial defects that affect carrier concentrations in the active layer as well as charge transfer and recombination at the interface. Using vacuum thermally-evaporated tin oxide as a case study, we highlight electrochemical tests that are simple yet screen device-relevant contact layer properties, making them useful for process development and quality control. Specifically, we show that cyclic voltammetry and potent…
In the present study, we report the synthesis and characterization of a low-temperature solution-processable monodispersed nickel cobaltite (NiCo2O4) nanoparticles via a combustion synthesis using tartaric acid as fuel and demonstrate its performance as hole transport layer (HTL) for Perovskite Solar Cells (PVSCs). NiCo2O4 is a p-type semiconductor consisting of environmentally friendly, abundant elements and higher conductivity compared to NiO. We show that the combustion synthesis of spinel NiCo2O4 using tartaric acid as fuel can be used to control the NPs size and provide smooth, compact an…
Perovskite solar cells (PSCs) with transparent electrodes can be integrated with existing solar panels in tandem configurations to increase the power conversion efficiency. A critical layer in semi-transparent PSCs is the inorganic buffer layer, which protects the PSC against damage when the transparent electrode is sputtered on top. The development of n-i-p structured semi-transparent PSCs has been hampered by the lack of suitable p-type buffer layers. In this work we develop a p-type CuOx buffer layer, which can be grown uniformly over the perovskite device without damaging the perovskite or…
Solution-processed quantum dots (QDs) have a high potential for fabricating low cost, flexible and large-scale solar energy harvesting devices. It has recently been demonstrated that hybrid devices employing a single monovalent cation perovskite solution for PbS QD surface passivation exhibit enhanced photovoltaic performance when compared to standard ligand passivation. Herein we demonstrate that the use of a triple cation Cs0.05(MA0.17FA0.83)0.95Pb(I0.9Br0.1)3 perovskite composition for surface passivation of the quantum dots results in highly efficient solar cells, which maintain 96 % of th…
The wide band gap methylammonium lead bromide perovskite is promising for applications in tandem solar cells and light-emitting diodes. Despite its utility, there is only a limited understanding of its reproducibility and stability. Herein, the dependence of the properties, performance, and shelf storage of thin films and devices on minute changes to the precursor solution stoichiometry is examined in detail. Although photovoltaic cells based on these solution changes exhibit similar initial performance, the shelf-storage depends strongly on the precursor solution stoichiometry. While all devi…
Cui et al. describe the fabrication and characterization of planar pn-junction solar cells based on lead-halide perovskites. The doping densities measured using Hall effect measurements vary from $N_D = 10^{12} cm^{-3}$ to $8\times 10^{12} cm^{-3}$ for the solution-processed n-type layer and $N_A = 8\times 10^9 cm^{-3}$ for the evaporated p-type layer. While these devices outperform their counterparts, that are supposedly un-doped, the results raise three important questions: (i) Are the reported doping densities high enough to change the electrostatic potential distribution in the device from…
Photovoltaic potential of tin perovskites revealed through layer-by-layer investigation of optoelectronic and charge transport properties
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH（亥姆霍兹柏林材料与能源有限公司）；Egyptian Petroleum Research Institute（埃及石油研究所）；IPVF, Institut Photovoltaïque d'Ile-de-France（法兰西岛光伏研究所）；University of Naples Federico II（那不勒斯费德里科二世大学）；Henan University（河南大学）；University of the Basque Country UPV/EHU（巴斯克国立大学）；Bielefeld University（比勒费尔德大学）
For almost sixty years, solar energy for space applications has relied on inorganic photovoltaics, evolving from solar cells made of single crystalline silicon to triple junctions based on germanium and III-V alloys. The class of organic-based photovoltaics, which ranges from all-organic to hybrid perovskites, has the potential of becoming a disruptive technology in space applications, thanks to the unique combination of appealing intrinsic properties (e.g. record high specific power, tunable absorption window) and processing possibilities. Here, we report on the launch of the stratospheric mi…
One of the most significant features of lead-halide perovskites are their ability to have comparably slow recombination despite the fact that these materials are mostly processed from solution at room temperature. The slow recombination allows achieving high open-circuit voltages when the lead-halide perovskite layers are used in solar cells. This perspective discusses the state of the art of our understanding and of experimental data with regard to recombination and open-circuit voltages in lead-halide perovskites. A special focus is put onto open questions that the community has to tackle to…
Detection and direct power conversion of high energy and high intensity ionizing radiation could be a key element in next generation nuclear reactor safety systems and space-born devices. For example, the Fukushima catastrophe in 2011 could have been largely prevented if 1\% of the reactor's remnant radiation ($γ$-rays of the nuclear fission) were directly converted within the reactor to electricity to power the water cooling circuit. It is reported here that the hybrid halide perovskite methylammonium lead triiodide could perfectly play the role of a converter. Single crystals were irradiated…
Due to their exceptional photovoltaic properties, metal halide perovskites (MHPs) are extensively studied for their potential applications in solar cells. In recent years, the power conversion efficiencies of MHPs-based solar cells rapidly increased from the initial few \% towards more than 25\,\% for single-junction devices. Therefore, also taking into account their low costs and ease of manufacturing, MHPs-based solar cells have become the fastest-advancing photovoltaic technology. In this regard, much of the recent work has been dominated by absorber materials based on methylammonium MHPs, …
The establishment of a rigorous theory on thermodynamics of light management in photovoltaics that accommodates various loss mechanisms as well as wave-optical effects in the absorption and reemission of light is at stake in this contribution. To this end, we propose a theoretical framework to calculate the open-circuit voltage enhancement resulting from photon recycling ($ΔV^{\mathrm{PR}}_{\mathrm{oc}}$) with rigorous wave-optical treatment. It can be applied to both planar thin-film and nanostructured single-junction solar cells. We derive an explicit expression for $ΔV^{\mathrm{PR}}_{\mathr…
Methylammonium lead iodide (MAPI) is the archetype of the intensively researched class of perovskites for photovoltaics. Nonetheless, even equilibrium aspects are far from being fully understood. Here we discuss equilibrium space charge effects at the MAPI/TiO2 and MAPI/Al2O3 interfaces, which are of paramount significance for solar cells. Different from the photovoltaic literature in which such built-in potentials are considered as being generated solely by electronic charge carriers, we will apply a generalized picture that considers the equilibrium distribution of both ionic and electronic …
Hybrid perovskites have received tremendous attention due to their exceptional photovoltaic and optoelectronic properties. Among the two widely used perovskite solar cell device architectures of n-ip and p-i-n, the latter is interesting in terms of its simplicity of fabrication and lower energy input. However this structure mostly uses PEDOT:PSS as a hole transporting layer which can accelerate the perovskite solar cell degradation. Hence the development of stable, inorganic hole extraction layers (HEL), without compromising the simplicity of device fabrication is crucial in this fast-growing …
In spite of intensive studies on the chalcogenides as conventional thermoelectrics, it remains a challenge to find a proper material with high electrical but low thermal conductivities. In this work, we introduced a new class of thermoelectrics, Ge-based inorganic halide perovskites \ce{CsGeX3} (X = I, Br, Cl), which were already known as a promising candidate for photovoltaic applications. By performing the lattice-dynamics calculations and solving the Boltzmann transport equation, we revealed that these perovskites have ultralow thermal conductivities below 0.18 W m$^{-1}$ K$^{-1}$ while ver…
Perovskite solar cells employing self assembled monolayers such as Me-4PACz as hole transport layer has been reported to demonstrate high device efficiency. However, the poor perovskite wetting on the Me-4PACz caused by poor perovskite ink interaction with the underlying Me-4PACz presents significant challenges for fabricating efficient perovskite devices. A triple co-solvent system comprising of dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and N-methyl-2-pyrrolidone (NMP) is employed to improve the perovskite ink-substrate interaction and obtain a uniform perovskite layer. In comparison…
Tin fluoride (SnF2) is an indispensable additive for high-efficiency Pb-Sn perovskite solar cells (PSCs). However, the spatial distribution of SnF2 in the perovskite absorber is seldom investigated while essential for a comprehensive understanding of the exact role of the SnF2 additive. Herein, we revealed the spatial distribution of SnF2 additive and made structure-optoelectronic properties-flexible photovoltaic performance correlation. We observed the chemical transformation of SnF2 to a fluorinated oxy-phase on the Pb-Sn perovskite film surface, due to its rapid oxidation. In addition, at t…
The ideal band gap for a photovoltaic active layer for the solar spectrum is around 1.3 eV. However oxides with such values are rare. One of the most studied oxides to date as a photovoltaic active layer is the cuprous oxide Cu2O. Its band gap is around 2.1 eV and is therefore not ideal for the solar spectrum. Power Conversion Efficiency generally do not exceed 4%. In this paper we propose to study an emerging type of solar cell that is based on ferroelectricity. In this type of solar cell, a p-n junction is not necessarily required, unlike conventional solar cells. Interesting conversion effi…
Solvent engineering offers fine control over the photovoltaic efficiency, film morphology, and crystallization quality of perovskite films and also enables to optimize light transmittance and absorbance in solar cell applications. In the present work, the band gap and reflectance were reduced through solvent engineering. We found that perovskite thin films produced using DMF (Dimethyl formamide) solvent had a band gap that was 0.24 eV less than those produced using IPA (Isopropyl Alcohol) solvent. Perovskite thin films produced using DMF solvent also exhibited considerably lower solar spectrum…
Halide perovskites have emerged recently as promising materials for many applications in photovoltaics and optoelectronics. Recent studies of their optical properties suggest many novel opportunities for a design of advanced nanophotonic devices due to low-cost fabrication, high values of the refractive index, existence of excitons at room temperatures, broadband bandgap tunability, high optical gain and nonlinear response, as well as simplicity of their integration with other types of structures. This paper provides an overview of the recent progress in the study of optical effects originatin…
Novel photovoltaics, such as perovskites and perovskite-inspired materials, have shown great promise due to high efficiency and potentially low manufacturing cost. So far, solar cell R&D has mostly focused on achieving record efficiencies, a process that often results in small batches, large variance, and limited understanding of the physical causes of underperformance. This approach is intensive in time and resources, and ignores many relevant factors for industrial production, particularly the need for high reproducibility and high manufacturing yield, and the accompanying need of physical i…
Recent observations indicated that the photoelectric conversion properties of perovskite materials are intimately related to the presence of superlattice structures and other unusual nanoscale features in them. The low dimensional or mixed dimensional halide perovskite family are found to be more efficient materials for device application compared to 3-dimensional halide perovskites. The emergence of perovskite solar cell has revolutionized the solar cell industry because of their flexible architecture and rapidly increased efficiency. Tuning the dielectric constant, charge separation are the …
Studies of emerging photovoltaics, such as organic and perovskite solar cells, have recently shown that the separation of photo-generated charge carriers is correlated with non-thermal, coherent oscillations within the illuminated device. We consider this experimental evidence in light of results from the theory of open quantum systems that point to the need for a self-oscillating internal capacitor, acting as a microscopic piston, to explain how an illuminated solar cell operates as an autonomous heat engine. We propose a picture of work extraction by photovoltaic devices that supersedes the …
