Research progress in large-area perovskite solar cells
The record power conversion efficiency of perovskite solar cells (PSCs) has impressively exceeded 25% in 10 years due to composition engineering, perovskite film growth control and perovskite/transport layer interface modification. However, the high efficiency PSCs are usually small-area (<0.1 cm2). For commercial application, the preparation of large-area devices is the necessary step for the development of PSCs.
At present, a series of research progress in large-area PSCs was summarized by the research team led by Prof. Jingbi You from Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China This paper summarizes the key technologies in the preparation of high-performance large-area PSCs. By optimizing the preparation method of large-area modules, growing high-quality perovskite films, reducing carrier recombination centers, and selecting appropriate charge transport layer to obtain high-performance devices, which will help the commercial development of large-area PSCs (Fig. 1). It was published in Photonics Research, Vol. 8, Issue 7, 2020 （Yang Zhao, Fei Ma, Feng Gao, Zhigang Yin, Xingwang Zhang, Jingbi You. Research progress in large-area perovskite solar cells[J]. Photonics Research, 2020, 8(7): 070000A1）and was chose as On the Cover of Special Issue on Perovskite Photonics.
Fig. 1. Summary of the article content
At present, high-efficiency small-area PSCs are generally prepared by spin-coating. There is still a gap in the photoelectric conversion efficiency (PCE) between small-area PSCs and large-area PSCs. It is difficult to obtain high-quality perovskite films by spin-coating (>1 cm2). In order to prepare a high-efficiency large-area PSCs, the preparation method，the preparation conditions of the perovskite and carrier transport layer need to be further improved.
1. Deposition Methods of Large-area PSCs
In order to obtain a uniform and high-quality perovskite film, large-area film preparation methods, such as Blade coating, Slot-Die coating, Spray coating, Inkjet printing and Roll-to-Roll, are applied to the preparation of PSCs (Fig. 2).
The performance of the large-area PSCs could be further improved by optimizing the preparation details of the large-area preparation methods, for example, substrate heating and n2 flow assisted film formation.
Fig. 2. Deposition methods of large-area PSCs. a-f are Spin-coating, Blade coating, Slot-Die Coating, Spray Coating, Inkjet Printing and Roll to Roll, respectively.
2. Growth of High-quality Large-area PSCs
The method for preparing high-efficiency small-area PSCs can also be applied to the preparation of large-area devices. The perovskite light-absorbing layer determines the performance of the devices, and high-quality perovskite films can be prepared by adjusting the perovskite precursor solution, thereby improving the performance of large-area PSCs. For example, through the optimization of the solvent for dissolving the perovskite, the adjustment of the composition of the perovskite components, and the auxiliary film formation of additives, a uniform and high-quality perovskite light-absorbing layer can be prepared (Fig. 3).
Fig. 3. Different methods of preparing highly perovskite films, a-d are the Solvent engineering, Composition engineering and additives engineering, respectively.
3. Fabrication of Large-area Charge Transport Layers
The carrier transport layer plays a role in the extraction and transport of carriers in the PSCs. In large-area PSCs, a suitable carrier transport layer needs to be selected.
In many research reports, the carrier transport layer has been optimized (Fig. 4). Taking Spiro-OMeTAD as an example, Spiro-OMeTAD is the first choice for high-efficiency PSCs, but the performance of its devices in the preparation of large-area devices is affected due to its faster crystallinity. Cheng et al. modified Spiro-OMeTAD and used Bifluo-OMeTAD as the hole transport layer of the device, which suppressed the rapid crystallization of the hole transport layer during the slot-die printing process, thereby improving the performance of the device. This work provides a new idea for the selection of the appropriate carrier transport layer.
Fig. 4. (a, b) Structure and J-V curve of the device with the doped charge carrier extraction layers. (c, d) Comparison of the Bifluo-OMeTAD and Spiro-OMeTAD and J-V curve of devices. (e, f) Device structure and I-V curve of using P3HT as the HTL. (g, h) The DFT simulation of GO and Cl-GO and PL spectra and TRPL spectra for different films.
4. Outlook and summary
(1) The efficiency of large-area PSCs is far behind that of small-area PSCs. By optimizing the preparation method, adjusting the composition, and optimizing the selection of the carrier transport layer, high-performance large-area PSCs can be obtained.
(2) Compared with traditional solar cells, the stability of PSCs is poor, and the stability of large-area PSCs needs to be further improved.