Abstract
It is the defects that determine the physicochemical properties and photoelectrical properties of the corresponding semiconductors. Controlling defects is essential to realize high-efficiency and stable solar cells, particularly in those based on hybrid halide perovskite materials. Here, we review the defect chemistry in perovskite absorbers, most of which take effects at grain boundaries and surfaces. These defects impact kinetics and/or thermodynamics during the courses of charge recombination, ion migration, and degradation in the corresponding devices, which inevitably influences their efficiency and stability. The effective suppression of harmful defects in perovskite photovoltaics not only reduces non-radiative recombination centers to improve the efficiency, but also retards their degradation under aging stresses to dramatically improve their long-term operational stability. Finally, the future challenges with regard to the in-depth understanding of defects formation, migration, and their passivation are presented, which shed light on realizing high-efficiency and stable perovskite optoelectronics.
Highlights
The tunable direct bandgap for perovskite absorbers from 1.2 to 3.0 eV obtained by simple composition engineering allows the fabrication of perovskite/silicon and all perovskite tandem solar cells with theoretical photoelectric conversion efficiency (PCE) limit beyond 30%, surpassing the Shockley– Queisser efficiency limit of single-junction solar cells.[19,20,21,22,23]
High temperature facilitates the diffusion of extrinsic ion in carrier transport layer and metal counter electrode, which bring about the ohmic contact and device architecture degradation, greatly shaking the foundations of stability in perovskite solar cells
The rapid development partially relies on the in-depth understanding of defects evolution and relevant suppression strategies
Summary
As a promising next-generation photovoltaic materials candidate, hybrid halide perovskites possess a general formula of ABX3, wherein A presents methylammonium (MA), formamidinium (FA), or cesium (Cs); B is lead (Pb) or tin (Sn) cation; and X often presents halogen (I, Br, or Cl) anions.[1,2,3,4,5] Within nearly one decade, hybrid halide perovskite-based photovoltaics have achieved incredible progress, which is originated from their superior optical and electronic properties, such as high light absorption coefficient (∼105 cm−1), balanced ambipolar carrier transport, long carrier diffusion lengths (>1 μm), high charge mobility (∼10 cm[2] V−1 s−1), and low exciton binding energy (∼10 meV) in polycrystalline perovskite absorbers.[6,7,8,9,10,11,12,13,14] These excellent optical and electronic properties, combining with its superior defect tolerance, meet many of the requirements for a high-efficiency optoelectronic technology.[15,16,17,18] the tunable direct bandgap for perovskite absorbers from 1.2 to 3.0 eV obtained by simple composition engineering allows the fabrication of perovskite/silicon and all perovskite tandem solar cells with theoretical photoelectric conversion efficiency (PCE) limit beyond 30%, surpassing the Shockley– Queisser efficiency limit of single-junction solar cells.[19,20,21,22,23] Their nature abundance and solution processable fabrication compatibility enlightened the low-cost photovoltaic technology revolution, with competitive levelized cost of electricity (LCOE) than that of crystalline silicon solar cells.[24,25,26,27]. Many characterization methods to analyze defects density in perovskite films and corresponding devices have been developed, including space charge limited current (SCLC),[29,45] thermal admittance spectroscopy (TAS),[46,47] thermally stimulated current (TSC) measurement,[17,48] deep-level transient spectroscopy (DLTS),[32] absolute photoluminescence (PL) emission,[49] ideality factor (IF),[50] and recently proposed drive-level capacitance profiling (DLCP) approach.[51]. These efforts have largely underpinned the rapid development of perovskite solar cells, with the efficiency over 25%. Recent significant strategies with regard to the defects manipulation facilitated both efficiency and stability improvement have been investigated deeply to provide a useful guidance for further breakthroughs of perovskite solar cells
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