Among various coating techniques, blade coating is one promising alternative for upscaling perovskite photovoltaic devices from small area research cells to intermediately sized cells and modules. Also, it is potentially compatible for future roll-to-roll processing.

We present planar inverted (p-i-n) solution processed perovskite solar cells. Besides the indium tin oxide and metal electrodes, all layers were processed from solution. The perovskite absorber layer is deposited via blade coating in a one-step process, employing lead(II) acetate trihydrate as lead source. The active area of the cells was increased to 1.1 cm². It has been found that control of the perovskite layer drying before annealing is most critical for device function. We compare various drying approaches by temperature and/or blowing with a directed nitrogen stream and demonstrate a large impact on cell performance. Detailed analyses using photoluminescence spectroscopy, X-ray diffraction measurements and scanning electron microscopy reveal a strongly enhanced layer quality and crystallinity upon controlled drying, resulting in power conversion efficiencies of 10.3%. Small scale devices with the same architecture yield values of around 14%, comparable to literature values [1],[2]. Blade coated samples show approximately 100 mV lower open-circuit voltages which is attributed to an increased rate of non-radiative recombination as confirmed by photoluminescence measurements. Furthermore, dark lock-in thermography, laser beam induced current measurement and photoluminescence mapping resolved coating defects and pinholes within the active area, additionally limiting device performance.

Upon replacement of PEDOT:PSS against a NiO_x hole transport layer, the efficiency of blade coated cells was increased to 12.4%. In comparison to spin coated cells with small active area, reaching 16.8% efficiency, the open circuit voltage offset is negligible. This is due to a generally higher coating quality and better formation of the perovskite layer on top of NiO_x. The performance limitation of the blade coated cells arises from an increased series resistance of the cells, which is currently being investigated. In a next step mini-modules are fabricated featuring three cells monolithically interconnected in series with an active area of 5.9 cm². This shall demonstrate the potential for further upscaling to larger areas.

[1]   D. Liu et al., J. Mater. Chem. A 5, 5701–5708 (2017).

[2]   K. A. Bush et al., Adv. Mater. 28, 3937–3943 (2016).