Deep Defect States in Wide-Band-Gap ABX₃ Halide Perovskites

Abstract

Lead bromide-based halide perovskites are of interest for wide-band-gap (>1.75 eV) absorbers for low-cost solar spectrum splitting to boost solar-to-electrical energy conversion efficiency/area by adding them to c-Si or Cu(In,Ga)Se 2 PV cells and for photoelectrochemical solar fuel synthesis. Deep in-gap electronic states in PV absorbers serve as recombination centers and are detrimental for the cell's photovoltaic performance, especially for the open-circuit voltage (V oc ). We find four different deep defect states in polycrystalline layers of mixed-cation lead tribromide from highsensitivity modulated surface photovoltage (SPV) spectroscopy. Measurements were performed with different contact configurations, on complete solar cells and on samples before and after aging or stressing at 85 °C under illumination. Three of the four states, with energies of ∼0.63, 0.73, and 1.35 eV below the conduction band edge, are assigned to intrinsic defects, whereas defect states in the middle of the band gap could be associated with (uncontrolled) impurities.

2D/3D Heterostructure for Semitransparent Perovskite Solar Cells with Engineered Bandgap Enables Efficiencies Exceeding 25% in Four‐Terminal Tandems with Silicon and CIGS

“…The enhanced V OC deficit in PSCs employing high bromide contents is commonly observed in literature and attributed to increased recombination losses in wide‐bandgap PSCs. [ 3,51,52,75,79,81 ] Impressively, PSCs with 2D/3D heterostructure demonstrate an enhancement in V OC of ≈45 mV for all studied bandgaps compared to the 3D reference devices (Figure 1a). We mainly attribute this enhancement to reduced non‐radiative recombination losses by formation of a 2D‐RP interlayer, which passivates the surface of the 3D double‐cation perovskite layer.…”

“…[ 3,52,69,73,74 ] A common issue is photo‐induced phase segregation and subsequent funneling of charge carriers into iodide‐rich lower bandgap regions, [ 75 ] acting as radiative recombination centers. [ 68,69,74–80 ] In addition, a higher density of defect states [ 41,79,81,82 ] and stronger interfacial recombination (e.g., due to energy level offsets) [ 51,79,83–87 ] have been proposed to increase non‐radiative recombination losses. Finally, the concentration of vacancy defects and strength of phase segregation seem to be directly linked to each other.…”

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.…”

“…thermally stimulated current (TSC), capacitance-frequencyat different temperatures (C-f), transient photocapacitance (TPC), surface photovoltage (SPV) spectroscopy, [45] timeresolved spectroscopies such as transient absorption and reflection techniques, [46] ultraviolet photoemission spectroscopy (UPS), [42b,47] scanning tunneling microscopy (STM). [19, 25d, 48] Comprehensive Reviews describing the working principles of techniques above and summarizing advantages and disadvantages can be found in Refs.…”

Verringerung schädlicher Defekte für leistungsstarke Metallhalogenid‐Perowskit‐Solarzellen

“…Mehrere zuvor entwickelte Techniken zum Verständnis der Eigenschaften von Defekten (Energieniveaus und Dichten) in anorganischen Halbleitern wurden auch in Perowskiten angewendet . Diese Techniken beinhalten Messungen des temperaturabhängigen raumladungsbegrenzten Stroms (SCLC), thermische Admittanzspektroskopie (TAS), DLTS (deep‐level transient spectroscopy), Laplace‐DLTS, stationäre Photolumineszenz (SSPL), zeitaufgelöste Photolumineszenz (TRPL), PL‐Mapping, zeitaufgelöste Mikrowellenleitfähigkeit (TRMC), thermisch stimulierte Strommessungen (TSC), Kapazitäts‐Frequenz‐Messungen bei verschiedenen Temperaturen (C‐f), transiente Photokapazitätsmessungen(TPC), Oberflächen‐Photospannungs (SPV)‐Spektroskopie, zeitaufgelöste Spektroskopien wie transiente Absorptions‐ und Reflexionsmessungen, UV‐Photoemissionsspektroskopie (UPS) und Rastertunnelmikroskopie (STM) . Umfassende Übersichtsarbeiten, die die Funktionsprinzipien der oben genannten Techniken beschreiben und Vor‐ und Nachteile zusammenfassen, findet man in Lit.…”