An Overview of the Types of Perovskite Solar Cells

Key Takeaways

• The basic structure of a perovskite solar cell consists of an electron transporting layer (ETL), a hole transporting layer (HTL), an anode, and a cathode. 

• Perovskite solar cells are classified as regular n-i-p and inverted p-i-n structures, depending on which transport material on the exterior portion of the perovskite encounters light rays first.  

• In the n-i-p structure of perovskite solar cells, the electron ETL is deposited first, whereas the HTL is deposited first in p-i-n structures.

Imagine you are going to purchase a phone online. You find a phone that you like listed on two different websites at the same price. The only difference between the two offers is the warranty period—only one website offers an extended warranty. Which website do you choose to purchase the phone from? Most likely, you would choose to purchase the phone from the site that offers an extended warranty. When companies make large investments in solar power generation projects, they have to make a similar decision, except instead of choosing a phone warranty, they have to choose between the service life of solar panels. 

The service life of solar panels defines the cost of a solar project. Perovskite solar cells are the rising star of the photovoltaic world, as their low cost and high conversion efficiency make them popular and affordable. Even though the bankability of perovskite solar cells has yet to be validated globally, due to their limited service life compared to silicon solar panels, extensive research into the field has produced different types of perovskite solar cells for commercial use.

In this article, we will discuss the advantages of different types of perovskite solar cells. 

The Advantages of Perovskite Solar Cells

An enormous amount of research has been conducted on perovskite materials. However, the service life of perovskite solar cells is less than silicon solar cells, and they suffer from instability and degradation issues. Given this, you might be wondering why perovskite research is still getting funded. Perovskite solar cells are still of interest to researchers for two main reasons: 

1. The power conversion efficiency of perovskite solar cells is high and inexpensive compared to existing photovoltaic cell technologies.

2. Perovskite tops the list when comparing open-circuit voltage versus bandgap. The photon energy lost during the conversion of light to electricity is less in perovskite solar cells compared to other cells.

The Configuration of Perovskite Solar Cells

Perovskite solar cell configuration plays a significant part in increasing the performance of the cells. The basic structure of a perovskite solar cell consists of an electron transporting layer (ETL) and a hole transporting layer (HTL), where the free electrons and holes get injected into. Usually, the anode and cathode in the perovskite solar cell structure are formed by Fluorine-doped tin oxide (FTO) glass and metal. 

The Different Types of Perovskite Solar Cells

Depending on which transport material (either electron or hole) on the exterior portion of the perovskite encounters the light rays first, perovskite solar cells are classified as:

• Regular n-i-p structures

• Inverted p-i-n structures

The n-i-p and p-i-n structures are further classified as:

• Mesoscopic structures—contains a mesoporous perovskite layer in the architecture.

• Planar structures—incorporates all planar layers.

Regular N-I-P Structures

In the n-i-p structure of perovskite solar cells, the electron ETL is deposited first, followed by HTL. The ETL encounters the sunlight first in this type of perovskite solar cell. The regular n-i-p perovskite solar cell structure comes in two architectures:

• N-i-p mesoscopic configuration—the mesoporous metal oxide consisting of perovskite is sandwiched between ETL and HTL. The cathode is a transparent glass and a metallic cap acts as the anode.

• N-i-p planar configuration—avoids the presence of a mesoporous metal oxide layer and makes the whole architecture simple. In an n-i-p planar structure, the perovskite light-harvesting layer is placed between ETL and HTL. The efficiency of planar n-i-p can be increased by controlling the interfaces between the various layers in the planar perovskite solar cell structure. N-i-p planar perovskite solar cells exhibit higher open-circuit voltage and short-circuit current density compared to the mesoscopic n-i-p structure. The current density-voltage hysteresis is a major drawback of planar n-i-p perovskite solar cells. 

Inverted P-I-N Structures

In inverted p-i-n planar perovskite solar cells, the HTL is deposited first and the light falls first on HTL before it encounters ETL. The capability of perovskite materials to transport holes themselves led to the development of planar heterojunction inverted p-i-n perovskite solar cells. Organic, inorganic, and oxide HTL materials are used to construct mesoscopic inverted p-i-n perovskite solar cells. The planar inverted p-i-n structure perovskite solar cells offer the advantages of low-temperature processing, high efficiency, and negligible hysteresis behavior. 

Apart from mesoscopic and planar n-i-p and p-i-n type solar cells, other types of perovskite solar cells include:

• ETL free configurations

• HTL free configurations

• Perovskite-silicon tandem architectures

Each configuration of perovskite solar cells have their own advantages and disadvantages. Still, research in this area continues, and new, low-cost types of perovskite solar cells will emerge, hopefully providing outstanding conversion efficiency and a long service life free from degradation problems. 

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