Publication date: 15th July 2022
Organo-halide perovskites exhibit excellent properties ideal for many optoelectronic devices, such as light emitting diodes (LEDs), solar cells or photodetectors. Due to their spectral purity, bandgap tunability and low cost have potential in high-brightness, large-area, and flexible LEDs. To further improve the photoluminescence quantum yield, a substantial effort to suppress the non-radiative recombination and degradation process has to be made. For an improvement of the light emitting performance, a detailed understanding of perovskite growth and of the process of defect formation is crucial.
In our study, we used a simultaneous measurement of in-situ photoluminescence (PL) and grazing-incidence wide-angle X-ray scattering (GIWAXS) to observe the perovskite layer crystallization process in real-time. We show that the layer formation process can be divided into three stages:
The growth starts with nucleation and free growth of perovskite grains. According to the high PL intensity, the defect density remains at a very low level during this stage.
In the second stage, the PL intensity decreases by order of magnitude, although the perovskite GIWAXS signal proves continual film growth. It indicates the formation of defective grain boundaries, and the non-radiative charge carriers recombination takes place. Direct passivation of these defects during this growth stage will significantly increase the light emission efficiency.
During the final part, the perovskite film slowly decomposes into PbI2. This process passivates the surface, and the photoluminescence signal is partially recovered. This implies that although post-growth defect passivation is possible, it cannot cure all active recombination sites.
This combined technique provides direct control of perovskite growth and, more importantly, defect formation and eventual passivation. The most significant advantage of such an approach is that the addition of passivating agents can be precisely timed, and the effect immediately measured. With the correct timing, the formation of defects at grain boundaries may be suppressed. This will lead to a significant improvement of light emission efficiency.
We acknowledge the financial support of projects APVV-17-0352, APVV-15-0641, APVV-15-0693, APVV-19-0465, SK-CN-RD-18-0006, SK-AT-20-0006, APVV-14-0745, APVV-14-0120, VEGA 2/0059/21, VEGA 2/0041/21, ITMS 26230120002, ITMS 26210120002, and ITMS 26210120023. This work was performed during the implementation of the project Building-up Centre for Advanced Materials Application of the Slovak Academy of Sciences, ITMS project code 313021T081, supported by the Research & Innovation Operational Programme funded by the ERDF. The authors also acknowledge the support of the Operational Programme Research, Development, and Education financed by the European Structural and Investment Funds and the Czech Ministry of Education, Youth and Sports (CzechNanoLab Research Infrastructure LM2018110 and CZ.02.1.01/0.0/0.0/16_026/0008382 CARAT) and the National Key Research and Development Program of China (2017YFE0119700).
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