Adding a 1 micron-thick perovskite layer, the efficiency is increased by 3.73%
The CIGS base layer is about 2 microns thick (or two thousandths of a millimeter). After absorbing sunlight, the conversion efficiency is about 18.7%. However, adding a 1 micron-thick perovskite layer can increase efficiency.And the entire assembly sits on a glass substrate that’s about 2 millimeters thick.
The team used nanoscale interface engineering of the CIGS surface and a heavily doped poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) hole transport layer between the subcells that preserves open-circuit voltage and enhances both the fill factor and short-circuit current. A monolithic perovskite/CIGS tandem solar cell achieved a 22.43% efficiency, and unencapsulated devices under ambient conditions maintained 88% of their initial efficiency after 500 hours of aging under continuous 1-sun illumination.(The previous record of this type of tandem solar cells, reported in 2015 by a group at IBM’s Thomas J. Watson Research Center, was 10.9 percent.)
▲Fig. Effects of CMP on CIGS surface and resulting performance of CIGS solar cells. (A) Atomic force microscopy (AFM) image of the CIGS surface before CMP polishing. (B) AFM image of the CIGS surface after CMP polishing. (C) Cross-sectional SEM images of the CMP processing on the CIGS surface. (D) J-V curves of original CIGS solar cells and after CMP polishing with a step size of 0.02 V and a scan velocity of 0.1 V/s, measured under AM1.5G illumination. (E) EQE of original CIGS solar cells and after CMP polishing.
▲Fig. Performance of the perovskite/CIGS tandem cells. (A) Schematic and cross-sectional SEM image of the monolithic perovskite/CIGS tandem solar cell. (B) J-V curve (NREL-certified; see fig. S8) and efficiency at the maximum power point (inset) of the champion tandem device. (C) EQE spectra for the subcells of the monolithic perovskite/CIGS tandem solar cell. (D) Stability test of the monolithic perovskite/CIGS tandem solar cell. The unencapsulation device maintained 88% of their initial PCE after 500 hours of aging under continuous 1-sun illumination and maximum power point tracking at 30°C ambient environment. The inset shows that the device can recover 93% of its initial performance after a 12-hour resting period without load and illumination.
The team uses Enli Tec QE-R Perovskite Solar Cell Quantum Efficiency Measurement System to measure EQE spectra of perovskite and CIGS single junction solar cells.
Dual-layer tandem technique could eventually approach 30 % power conversion efficiency
Professor Yang said, “With our tandem solar cell design, we’re drawing energy from two distinct parts of the solar spectrum over the same device area. This increases the amount of energy generated from sunlight compared to the CIGS layer alone.” Professor Yang also said, “Our technology boosted the existing CIGS solar cell performance by nearly 20 percent from its original performance. That means a 20 percent reduction in energy costs." He added that devices using the two-layer design could eventually approach 30 percent power conversion efficiency. That will be the research group’s next goal.
The study was supported by the National Science Foundation and the Air Force Office of Scientific Research. Over the years, Professor Yang Yang and the team of Yang Yang Lab have been working on tandem solar cells, and have many internationally renowned research results, including transparent tandem solar cells that can be applied to windows.
Cited from: High-performance perovskite/Cu(In,Ga)Se2 monolithic tandem solar cells
Qifeng Han, Yao-Tsung Hsieh, Lei Meng, Jyh-Lih Wu, Pengyu Sun, En-Ping Yao, Sheng-Yung Chang, Sang-Hoon Bae, Takuya Kato, Veronica Bermudez, Yang Yang
Science31 Aug 2018; Vol. 361, Issue 6405, pp. 904-908; DOI: 10.1126/science.aat5055
References：Matthew Chin | August 30, 2018. Dual-layer solar cell developed at UCLA sets record for efficiently generating power. (UCLA NEWROOM)