An Introduction of Perovskite Solar Cells

Posted by alfachemistry on August 19th, 2019

Development of perovskite solar cells

In 2009, Akihiro Kojima, a professor at Yokohama University in Japan, first prepared CH3NH3PbI3 and CH3NH3PbBr3 as light absorbing layers for dye-sensitized solar cells, achieving 3.8% efficiency. Later, the perovskite material decomposes quickly due to the liquid electrolyte, so that the battery efficiency is quickly attenuated. But researchers quickly realized that perovskites absorb sunlight and carry electricity. In recent years, the development of perovskite solar cells have been rapid. With the continuous development of the preparation process and commercialization process, the photoelectric conversion efficiency of perovskite solar cells has increased from 3.8% in 2009 to 20.1%. Compared with the solar cells of the silicon era, the perovskite solar cell is expected to occupy a large share in the future solar cell industry.

Structure of perovskite solar cells

The name of the perovskite solar cell is derived from the fact that its light absorbing layer (CH3NH3PbIx) has a perovskite structure, not because it contains calcium titanate (CaTiO3). This type of organic-inorganic mixed metal halide-based perovskite structural semiconductor exists in the form of the common ABX3 wherein A is a monovalent organic cation, B is a metal cation, and X is a halogenated anion. The most commonly used organic-inorganic perovskite material is CH3NH3PbI3-x-yBrxCly (MAPbI3-x-yBrxCly). Perovskite solar cells are ideal for photovoltaics, semiconductor light sources, and even lasers. A highly crystalline film precursor can be prepared by a low temperature solution method, the band gap of which can be adjusted by modifying the halide component. Such perovskite solar cells exhibit excellent high photoluminescence lifetime and mobility. 

The main structure of the perovskite solar cell includes FTO conductive glass, dense layer, mesoporous layer, insulating layer, and carbon counter electrode.

FTO conductive glass

The primary role of conductive glass in batteries is to collect and transport electrons. Perovskite solar cells are generally made of fluorine-doped tin oxide conductive glass. The laser-etched FTO can be used as a base material.

Dense layer

The dense layer of TiO2 is generally an n-type semiconductor and functions to transport electrons. In general, the optimal thickness of the TiO2 dense layer is 50-100 nm, so as not to affect its series resistance.

Mesoporous layer

The TiO2 mesoporous layer is a thin film layer with electron transport function and channel function, and this layer is optional during the experiment.

Insulating layer

The ZrO2 insulation layer is printed primarily to avoid short-circuit of the battery.

Carbon counter electrode

Replacing the metal electrode with a carbon counter electrode not only reduces the cost, but also effectively improves the humidity stability of the battery.

Work mechanism of perovskite solar cells

The photoelectric conversion mechanism of a perovskite solar cell is as follows: When sunlight is irradiated onto the FTO, the perovskite light absorbing layer first absorbs photons to generate electron-hole pairs. Since the perovskite material has different binding ability to excited electron-hole pairs, and these perovskite materials tend to have low carrier recombination probability and high carrier mobility, so the diffusion length and lifetime of these carriers is long. The carrier diffusion length of methylaminoiodide (CH3NH3PbI3) reaches 100 nm, while the diffusion of chlorine-doped methylaminoiodide (CH3NH3PbI3-xClx) is even greater than 1 μm.

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