2023 Nano-Micro (IF:26.6)LettersCrystallization and Orientation Modulation Enable Highly Efficient Doctor-Bladed Perovskite Solar Cells
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Improving Perovskite Solar Cell Efficiency through Crystallization and Orientation Modulation by Blade Coating Technique: Breakthrough in Solar Technology
In the rapidly advancing field of solar technology, perovskite solar cells (PSCs) have emerged as promising contenders due to their exceptional optoelectronic properties. However, a major challenge lies in developing commercially viable and scalable manufacturing techniques. In a significant breakthrough, a research team led by Professor Yang Junliang, Vice Dean of the School of Physics and Electronics at Central South University, introduced a novel additive – Methylammonium Chloride (MACl) – to modulate the crystallization and orientation of perovskite thin films fabricated using the two-step sequential blade-coating process. This innovative approach significantly improved the quality of perovskite thin films and reached an impressive power conversion efficiency (PCE) of 23.14%.
The Potential of Perovskite Solar Cells:
Perovskite solar cells have garnered considerable research interest due to their high absorption coefficient, long carrier diffusion length, and low trap density. These characteristics have enabled PSCs to achieve certified PCEs of up to 25.7%. However, most high-efficiency PSCs are fabricated using laboratory-scale spin-coating deposition, which lacks scalability for large-scale production. Therefore, developing scalable manufacturing techniques is crucial for the commercialization of PSCs.
The PCE of PSCs fabricated through the two-step sequential deposition process significantly lags behind those fabricated using advanced spin-coating methods. The two-step sequential deposition process involves the reaction between organic salts and lead halides to bypass the uncontrolled nucleation process of perovskite thin films in a single-step process. However, Professor Yang Junliang’s research team aimed to address this performance disparity.
The Role of Methylammonium Chloride (MACl):
The research team introduced MACl to modulate the crystallization and orientation of perovskite thin films fabricated through the two-step sequential blade-coating process. MACl plays a crucial role in improving the quality of perovskite thin films. It increases grain size and crystallinity, reducing trap density and suppressing non-radiative recombination. Non-radiative recombination is an important loss mechanism in solar cells, where absorbed light energy is converted to heat instead of electricity. By suppressing non-radiative recombination, MACl significantly enhances the efficiency of solar cells.
Additionally, MACl promotes preferred orientation of the perovskite thin film’s (100) surface upwards. This orientation is more favorable for carrier transport and collection, resulting in a substantial improvement in the fill factor. The fill factor is a key parameter representing the maximum obtainable power and indicating the quality of the solar cell. Higher fill factors correspond to higher solar cell efficiency.
The introduction of MACl led to PSCs based on the ITO/SnO2/FA1-xMAxPb(I1-yBry)3/Spiro-OMeTAD/Ag structure achieving a maximum PCE of 23.14% and outstanding long-term stability. This structure represents a common architecture for PSCs, with ITO/SnO2 serving as the electron transport layer, FA1-xMAxPb(I1-yBry)3 as the perovskite absorber layer, Spiro-OMeTAD as the hole transport layer, and Ag as the electrode. The research team also achieved excellent PCEs of 21.20% for a 1.03 cm2 PSC and 17.54% for a small module with an area of 10.93 cm2. These results mark significant progress in the practical application of large-scale, high-performance two-step sequential deposition PSCs.
The research team led by Professor Yang Junliang from the School of Physics and Electronics at Central South University has made an important stride in the development of scalable manufacturing techniques for perovskite solar cells. The introduction of MACl to modulate the crystallization and orientation of perovskite thin films has proven to be a game-changing approach, greatly improving the quality of the films and significantly enhancing the power conversion efficiency.
Furthermore, the research team used the SS-X Solar Simulator from Enlitech to test the performance of the solar cells. The SS-X simulator utilizes a xenon short arc lamp as a broadband light source, possesses A+ level spectral matching capability, and offers various spot sizes ranging from 50mm to 220mm. The simulator features a patented automatic intensity adjustment function with an accuracy of up to 1%. It also has the capability to provide variable spectra, making it suitable for testing tandem solar cells. The use of AM1.5G filters manufactured using advanced plasma deposition technology ensures high spectral accuracy and long lifespan.
The superior spectral accuracy of the SS-X simulator makes it more suitable than other simulators for characterizing various types of novel solar cells, such as low-bandgap organic solar cells and perovskite/Si tandem solar cells. The SS-X simulator provides stable and continuous irradiation, avoiding characterization errors caused by the slow response times of the tested solar cells.
The work of this research team has not only achieved significant breakthroughs in the field of perovskite solar cells but also ensured the accuracy and reliability of experimental data through the advanced performance of the SS-X simulator from Enlitech.
Characterization of perovskite films fabricated via two-step doctor-blading. a XRD patterns of wet pristine perovskite films. b XRD patterns of perovskite films after annealing. c Steady-state PL emission spectra. d Time-resolved PL decay curves
Photovoltaic performance and optoelectronic properties of PSCs with perovskite films fabricated via two-step doctor-blading with the different ratios of MACl. a J–V curves and corresponding parameters of typical PSCs. b Light intensity dependence of the Voc of PSCs. c Mott–Schottky plots of the PSCs. d Fill factor limitation comprises nonradiative loss (blue area) and transport loss (pink area). e SCLC measurements of perovskite films. f Nyquist plots of EIS
Performance of OAI-modified PSCs and mini-module. a J–V curves. b Stabilized power output measured at the maximum power point (MPP). c Long-term stability measurements of OAI-modified device without encapsulation under ambient conditions with about 30% relative humidity. d J–V curves of 1.03 cm2 PSCs and 10.93 cm2 mini-module. Insets are the pictures of 1.03 cm2 PSCs and 10.93 cm2 mini-module