A Review of Common Characterization Methods for Perovskite Solar Cells
Chapter 1: Structural Characteristics and Photovoltaic Applications of Perovskite Materials
Perovskite solar cells (PSCs), representing the third generation of photovoltaic technology, are centered around using organic metal halide semiconductors with an ABX3 crystal structure as the light-absorbing layer. These materials are named after their similarity to the natural mineral CaTiO3 in crystal configuration, occupying cubic lattice vertex positions (coordinates 000) by A-site cations, body-centered positions (1/2 1/2 1/2) by B-site metal ions, and face-centered positions (1/2 1/2 0) by X-site halogen ions within space group Pm3m. This unique crystalline framework endows the material with excellent optoelectronic properties.
In terms of chemical composition, monovalent cations such as Cs+, CH3(NH3)+(MA+), or HC(NH2)2+(FA+) typically occupy the A site; these ions not only serve charge compensation but also adjust lattice parameters through size effects to optimize material band structures. The B site is primarily occupied by divalent metal ions like Pb2+ and Sn2+, whose d-orbital electronic states critically influence carrier mobility. The X site is filled with halogen ions such as I-, Br-, Cl-, or their mixtures; variations in halogen ratios allow precise tuning of band gaps within a range from 1.5 to 2.3 eV. This compositional tunability makes perovskites ideal 'designable' photovoltaic materials.
From a performance perspective, perovskites exhibit numerous outstanding advantages: first, they possess an extinction coefficient on the order of (10^5 ext{ cm}^{-1}), meaning that film thicknesses around 500 nm can achieve over 90% sunlight absorption; second, bipolar carrier transport characteristics enable both electron and hole diffusion lengths exceeding (1 mu m), significantly reducing bulk recombination losses; furthermore, solution processing capabilities facilitate low-temperature fabrication which greatly lowers production costs. Collectively, these features have propelled PSC efficiencies from just (3.8%) in (2009) to a certified current maximum efficiency of (25.7%), creating remarkable advancements in photovoltaic materials development.
Chapter 2: Microscopic Morphology Characterization Techniques
Scanning Electron Microscopy (SEM) serves as one direct tool for studying surface morphology in perovskite films. By comparing samples under different preparation conditions, researchers found significant correlations between grain sizes and device performances. In typical experiments without optimization controls showing average grain sizes around (200 nm) along with noticeable segregation at grain boundaries; however samples treated with NaAc seed layers exhibited increased grains above (300 nm), displaying columnar growth characteristics perpendicular to substrates—this oriented growth reduces lateral boundary numbers where deep-level defects predominantly accumulate leading directly to reduced non-radiative recombination centers across optimized films exhibiting single-crystal structures throughout their thickness ensuring efficient collection of photogenerated carriers.
Atomic Force Microscopy (AFM) provides quantitative information about nanoscale surface morphology revealing that increasing B-CQDs additive content from (0%) up to (5%) results in rising roughness values ((Ra) ranging from(13.076 nm o21 .046nm). Such increases stemmed mainly due crystallinity enhancements yielding uneven surfaces boosting scattering effects prolonging photon travel paths thus improving capture efficiencies while caution must be taken against excessive roughness potentially causing poor interfacial contacts necessitating balance between light absorption versus charge transport relationships. ... (Note: This article summarizes research findings published by scholars including Chen Ying and Yang Yuxuan among others in journals like Nano Energy and Chemical Engineering Journal.)