Scanning Probe Microscopy Applied to Organic–Inorganic Halide Perovskite Materials and Solar Cells

Abstract

preparation can lead to a large variety of film morphologies.OHPs have impressive optoelectronic properties, ranging from high absorption coefficient and suitable bandgap for visible light, [5] low exciton binding energy, [6,7] high carrier mobility, and long carrier diffusion lengths, [8] all of which make this class of materials especially suitable for PV applications. It is of the utmost importance to understand the effect that film morphology has on these critical properties, and subsequently on standard solar cell device parameters such as photocurrent, photovoltage, and PCE. OHP devices are also known to degrade under prolonged exposure to environmental factors including moisture, iodine vapor, high temperature, and sunlight. [9][10][11][12] Understanding how and why the film morphology and performance changes over time is also of key interest.Perovskite films are often characterized using conventional techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), quantum efficiency measurements, and I-V curve measurements, which lack high spatial resolution. However, scanning probe microscopy (SPM) techniques offer a unique advantage to correlate changes in optoelectronic properties and PV performance parameters with morphological features on the nanoscale. SPM techniques have been employed to characterize other PV technologies such as silicon, copper indium gallium selenide (CIGS), CdTe, GaAs, and organic solar cells. [13][14][15][16][17][18][19][20][21][22] Open-circuit voltage variation due to grain orientation and grain boundaries was revealed. [13] Moreover, SPM has been used to investigate the interfacial properties in polycrystalline Si [14] as well as in blended [15] and phase-segregated [16] organic solar cells. Furthermore, scanning-probe techniques demonstrated their ability to study molecules used for dye sensitized solar cells down to the atomic level. [20,21] In addition, SPM techniques can provide insight into phenomenon specific to OHPs. This includes film growth variation depending on fabrication technique, film degradation due to environmental factors, and undesirable current-voltage hysteresis possibly induced by ion migration within the OHP film. A wide variety of SPM techniques have been used to explore heterogeneities in OHP thin film properties (Figure 1a-c), including topographic atomic force micro scopy (AFM), Kelvin probe force microscopy (KPFM), scanning tunneling microscopy (STM), conductive-AFM (c-AFM), and scanning near-field optical microscopy (SNOM).To meet the increasing energy demands of the growing society, environmentally friendly and renewable energy sources are needed. Organicinorganic halide perovskites are a promising class of materials for building solar cells due to their easy fabrication, flexibility, and bandgap tunability. The highest efficiency achieved with these materials in the lab is comparable to conventional silicon solar cells currently on the market. However, their commercialization is hampered by certain challenges, such as stabil...

Reducing Detrimental Defects for High‐Performance Metal Halide Perovskite Solar Cells

“…Several techniques previously developed to understand the features of defects (energy levels and densities) in inorganic semiconductors were applied also in perovskites . These techniques include temperature‐dependent charge space limited current (SCLC), thermal admittance spectroscopy (TAS), deep‐level transient spectroscopy (DLTS), Laplace current DLTS (I‐DLTS), steady‐state photoluminescence (SSPL), time‐resolved photoluminescence (TRPL), PL mapping, time‐resolved microwave conductivity (TRMC), thermally stimulated current (TSC), capacitance‐frequency at different temperatures (C‐f), transient photocapacitance (TPC), surface photovoltage (SPV) spectroscopy, time‐resolved spectroscopies such as transient absorption and reflection techniques, ultraviolet photoemission spectroscopy (UPS), scanning tunneling microscopy (STM) . Comprehensive Reviews describing the working principles of techniques above and summarizing advantages and disadvantages can be found in Refs.…”

Emerging Conductive Atomic Force Microscopy for Metal Halide Perovskite Materials and Solar Cells

“…As for C‐AFM, this technique widely used to probe the electronic properties by measuring and recording current between conductive tip and the substrate in the contact mode. Under this scenario, the conductive tip sweeps across the substrate accompanied by a constant tip‐sample interaction force . As a derivative of AFM originated from the electrical mode of scanning probe microscopy, C‐AFM with a set of current amplifiers attached to the microscope can be devoted to imagining the morphology and characterizing local electrical properties of the sample surface simultaneously at microscopic scale, even under the ambient environment .…”

Probing the Microstructure of Methylammonium Lead Iodide Perovskite Solar Cells

“…In addition to the race for new efficiencies and finding ways to push the technology into market, a fundamental understanding of the energy conversion process within the perovskite thin films has started to develop. The latter not only provides handles to an enhanced energy conversion, but may also assist in improving the chemical and physical stability of the devices and eventually replacing the water‐soluble and ecotoxic lead‐halogen compound . To improve the understanding of light harvesting, photon‐to‐electron conversion and charge carrier transport, a detailed analysis of the microstructure and its properties is needed.…”