Solar cells can realize efficient conversion of solar energy to electric energy without environmental pollution and carbon emissions. Highly efficient solar cells will help to reach peak carbon emissions and achieve carbon neutrality.
Perovskite solar cells feature high efficiency, high defect tolerance, solution processes and low cost. They exhibit excellent performance in both single-junction and multi-junction solar cells. Noble metal electrodes inhibit reduction of the device cost, while the carbon electrodes of perovskite cells have the merits of low cost, simple preparation methods and high stability. Fully printable perovskite modules based on carbon electrodes with an area of >70 cm2 have achieved an efficiency of more than 13 percent so far, and show excellent stability.
However, there are insufficient interfacial points of contact and severe energy mismatches in perovskite/carbon electrode interfaces. In addition, the thermal treatment process of printed carbon electrodes can cause damage to the perovskite film beneath the carbon electrodes.
Carbon black interlayer improves the efficiency of all-inorganic perovskite solar cells based on carbon electrodes [IMAGE: SIC/CAS]
Recently, a research team led by Professor Yang Songwang of the Shanghai Institute of Ceramics (SIC), Chinese Academy of Sciences (CAS), has made progress in creating perovskite solar cells based on printed carbon electrodes. In order to improve the poor contact points in the carbon electrode/CsPbI2Br perovskite interface and energy level mismatches, they introduced carbon black nanoparticles to construct a carbon black interlayer and optimize the extraction of carriers.
The work function of the carbon black interlayer (-5.10 eV) is located between the valence band maximum of the CsPbI2Br perovskite (-5.44 eV) and the work function of the carbon electrode (-5.03 eV), which can reduce the interface energy mismatch.
The carbon black interlayer is also dense and uniform, which contributes to sufficiency of interfacial contact between the CsPbI2Br perovskite layer and the carbon electrode. The above advantages ensure an effective extraction of photogenerated holes, and the efficiency of the optimal device reaches 13.13 percent.
Moreover, the device based on the carbon black interlayer maintains about 90 percent of its initial efficiency after being continuously heated at 85℃ for 2,000 hours, showing good thermal stability of CsPbI2Br solar cells based on carbon electrodes.
Schematic diagram of the vacuum-assisted drying process of carbon electrodes and the ToF-SIMS element depth distribution of perovskite/CuSCN films [IMAGE: SIC/CAS]
Furthermore, in order to further enhance the efficiency of carbon-based solar cells, the team introduced an inorganic CuSCN hole transporting layer between the (CsFAMA)Pb(IBr)3 perovskite and the carbon electrode to improve the hole extraction and device efficiency. They demonstrated that the heating process of the carbon electrode under high temperature (~100℃) causes the diffusion of SCN- into the perovskite layer and therefore reduces the performance of the device.
To solve this problem, they developed a vacuum-assisted drying process for the preparation of carbon electrodes. This process can accelerate solvent volatilization at a lower temperature (<60℃), which inhibits SCN- diffusion caused by the heating process and improves the efficiency of the device to 15.72 percent.
Furthermore, the stability test showed that the device still maintained about 85 percent of its initial efficiency after 300 hours of continuous light soaking or 1,000 hours of storage (unencapsulated), indicating good stability.
The above results were published in ACS Applied Materials & Interfaces in articles entitled “CsPbI2Br Perovskite Solar Cells Based on Carbon Black-Containing Counter Electrodes” and “Vacuum-Assisted Drying Process for Screen-Printable Carbon Electrodes of Perovskite Solar Cells with Enhanced Performance Based on Cuprous Thiocyanate as a Hole Transporting Layer”.
Field test system for perovskite sub-modules [IMAGE: SIC/CAS]
In addition, Professor Yang’s team has developed large-area perovskite sub-modules (125 mm × 125 mm) based on the carbon electrodes. They have built a field test system to evaluate the outdoor performance of the perovskite sub-modules and also established a small-scale distributed electricity generation system based on the perovskite modules to evaluate their practical running properties.
For more information, please contact:
Professor Yang Songwang
Email: swyang@mail.sic.ac.cn
Shanghai Institute of Ceramics,
Chinese Academy of Sciences
Source: Shanghai Institute of Ceramics (SIC),
Chinese Academy of Sciences