Why Thick Perovskite Solar Cells Lose Efficiency — And a Simple Way to Fix It
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Abstract
Perovskite is a next-generation solar material that allows for higher efficiency, lower cost, and ultra-lightweight panels through its superior light absorption properties. Perovskite solar cells have thus become a leading technology in perovskite photovoltaics. They are highly efficient and low-cost solar cells that can be adapted to almost any surface. Their ability to capture even the slightest ray of light means they can outperform traditional solar panels.
However, like all technology, perovskite comes with its own set of challenges. A common problem that has arisen is that the performance of a perovskite film drops as its thickness increases.
This study shows that lattice strain relaxation is the main reason behind this efficiency loss in thick perovskite solar cells, even when electron-hole diffusion lengths and carrier lifetimes are long. The reason is that when compressive strain is released, it reduces charge transport, causing diminished current density and power conversion efficiencies (PCE).
To overcome this, we apply a Strain Retention Strategy (SRS) during the fabrication of perovskite films to preserve compressive strain in films over 2 microns thick. With SRS, inverted perovskite solar cells achieved a PCE of 23.5%. This performance is comparable to that of thin films and highlights a scalable route for improving the efficiency and stability of perovskite solar technology.
Introduction
Perovskite solar cells lie at the center of our research in the energy industry. These solar cells are highly efficient and can harvest light much better than traditional solar cells. They are also flexible, which means they can be adapted to many surfaces.
As research on perovskite solar cells progresses, we have observed that increasing the perovskite thickness to the level necessary for commercial solar modules often causes declines in performance.
Further research and observation revealed that lattice strain within lead iodide perovskite films affects how charge is transported and ultimately impacts the overall efficiency of the device.
The Unexpected Challenge of Thick Perovskite Layers
Thicker perovskite films, typically over 1 micron, improve light absorption and display better long-term stability in solar cells equipped with perovskite absorbers.
However, as the thickness increases, specific features such as short-circuit current density, fill factor, and overall power conversion efficiency (PCE) degrade. This hinders the development of perovskite technology for all types of devices, resulting in poorer long-term stability.
Even stranger was the fact that this occurs despite engineering films with long electron-hole diffusion lengths and excellent carrier lifetimes. The persistent drop in performance suggested that there are additional limiting factors beyond carrier recombination.
Cracking the Mystery: It’s All About Strain
Using benzamidine hydrochloride (BZM) as an additive in methylammonium lead iodide-based perovskite systems, researchers achieved exceptional carrier lifetimes exceeding 15 microseconds and diffusion lengths over 4 microns. This surpasses typical perovskite film thickness. However, thicker films still failed to display stable and efficient device performance.
Further research showed that lattice strain relaxation—a release of compressive strain within the crystal lattice—causes decreased carrier mobility and free carrier concentration. This, in turn, caused higher series resistance and lower efficiency.
A Simple Solution: The Strain Retention Strategy (SRS)
To combat strain relaxation, our team developed the Strain Retention Strategy (SRS), a subtle modification during the fabrication of perovskite films. This strategy involves sequential dripping in spin-coating, a technique that carefully controls crystallization and maintains compressive strain in films thicker than 2 microns.
The resulting inverted perovskite solar cells demonstrated a leap from 17.0% to 23.5% PCE. This level matches the performance of thin films and represents a significant step toward improved efficiency for perovskite solar cells. This means that even thicker cells can perform efficiently, and perovskite technology can be applied to a broader range of devices with the same high performance.
Why This Discovery Matters
This breakthrough focuses less on traditional limits, such as diffusion length, and more on the vital role of strain stabilization in halide perovskites. The approach allows perovskite technology to be scaled up for manufacturing purposes. The resulting high-efficiency solar cells can be used in a wider range of applications.
Additionally, these findings tell us how to further improve planar perovskite solar devices. They also offer valuable insights into tandem solar cells, including all-perovskite tandem and silicon tandem architectures.
What’s Next?
Smarter Interface Engineering
Future research will focus on improving surface passivation, energy level alignment, and buried interface stabilization. The goal is to reduce interfacial recombination and improve charge extraction in thick perovskite layers.
When we can optimize transport layers and hole-transport materials, we will maximize photovoltaic performance in high-efficiency devices.
Optimized Materials and Transport Layers
New developments and upgrades to perovskite technology, including innovative transport materials and additives that stabilize perovskite-substrate interfaces, deliver uniform crystal growth and consistent device quality.
The more we develop halide perovskite chemistry and lead halide perovskite precursors, the more we can include these cells in new applications. Stable and high-performing thick perovskite solar cells mean that this technology can be used in more fields.
Toward Tandems and Scalable Devices
Tandem solar cell architectures rely on thick perovskite absorbers.
Research is currently focusing on scalable inverted perovskite solar devices. These will combine optical and electrical optimizations for high-performance solar modules compatible with industrial manufacturing. This paves the way for high-efficiency solar cells with long-term stability.
CPTI for Your Perovskite Solar Cells
Are you ready for next-gen solar energy? Contact CPTI today to discover how our perovskite solar cells can upgrade your products. Partner with us for cutting-edge perovskite solutions tailored to your products and operations!
FAQs
Why do thicker perovskite solar cells lose efficiency?
Thicker perovskite solar cells often display incomplete charge extraction, increased interfacial recombination, and non-uniform crystal growth. These issues limit both the efficiency and stability of the device, especially at scale.
Can thick perovskite layers be used in tandem solar cells?
Yes, thick perovskite absorbers are particularly relevant for tandem solar cells, where maximizing light absorption is important. To achieve efficient and stable operation, researchers must focus on interface engineering and optimized transport layers.
What role do buried interfaces play in thick perovskite devices?
Buried interfaces, such as the junction between the perovskite and the hole transport layer, matter — a lot. Defects or misaligned energy levels at these interfaces can reduce the efficiency of charge extraction and increase recombination losses in thick films.
How can we improve the performance of thick perovskite solar cells?
Solutions include using high-performance perovskite modules, applying surface sulfidation, optimizing electron transport and hole transport materials, and stabilizing perovskite-substrate interfaces. These techniques can reduce recombination and deliver high-efficiency inverted perovskite architectures.
Are thick perovskite solar cells scalable for commercial use?
With advances in interface engineering, transport materials, and crystallization control, thick perovskite solar cells and modules show strong potential for scalable, commercial applications, particularly in flexible perovskite and all-perovskite tandem solar formats.