LAUSR

DOI: 10.1002/aenm.201903108 including polyethylene terephthalate (PET) and polyethylene naphthalate (PEN). Indium tin oxide (ITO) is still the best option for the transparent electrode. Deposition of transparent and conductive ITO by sputtering requires a substrate temperature higher than 200 °C to promote crystallization.[4] However, the glass transition temperatures of PET and PEN are around 78 and 120 °C, respectively.[5,6] As a consequence, ITO on polymer substrates has to be deposited at a low temperature such as room temperature, which yields amorphous ITO films. ITO on polymer substrates is much thicker to reduce the sheet resistance, and also less transparent, especially in the wavelength range around 400 nm (Figure S1, Supporting Information).[7,8] In addition, perovskite materials are known to be sensitive to moisture,[9–11] but polymer substrates have relatively high water vapor transmission rates (WVTR). For example, a 100 μm thick PET substrate has a WVTR higher than 3.9 g m−2 day−1 (at 37.8–40 °C).[12,13] It is not clear yet whether the encapsulation layers for perovskite flexible PV modules made on polymer substrate can still maintain their flexibility or not. Here, we report fabricating perovskite solar module directly on flexible Willow Glass which itself serves as encapsulation layer. Willow Glass not only retains the advantages of glass substrates, i.e., withstanding processing temperatures over 600 °C and a WVTR below detection limits (3 × 10−7 g m−2 day−1),[13] but also offers a good flexibility with the minimum bending radius of less than 100 mm, benefiting from its small thickness, typically 100 μm.[14] The ultrathin glass also enables the manufacturing of lightweight PV modules, fulfilling requirements in emerging markets such as portable power supplies and electric vehicles which need solar panels to be as light as possible. Moreover, the flexible glass is compatible with roll-to-roll fabrication processing, where scalable solution coating strategies such as blade coating and slot-die coating can be applied to realize high throughput and high-speed manufacturing. We demonstrate a large-area, high-efficiency flexible perovskite solar module with perovskite films fabricated by blade coating on ITO coated Willow Glass. Ammonium chloride (NH4Cl) was added in precursor solution to improve the perovskite film morphology by retarding perovskite nucleation. Meanwhile, similar to many ammonium halides, NH4Cl can passivate perovskite films, improving the performance of devices. As a result, the PCE of a flexible perovskite module Perovskite materials are good candidates for flexible photovoltaic applications due to their strong absorption and low-temperature processing, but efficient flexible perovskite modules have not yet been realized. Here, a record efficiency flexible perovskite solar module is demonstrated by blade coating high-quality perovskite films on flexible Corning Willow Glass using additive engineering. Ammonium chloride (NH4Cl) is added into the perovskite precursor solution to retard the nucleation which prevents voids formation at the interface of perovskite and glass. The addition of NH4Cl also suppresses the formation of PbI2 and reduces the trap density in the perovskite films. The implementation of NH4Cl enables the fabrication of single junction flexible perovskite solar devices with an efficiency of 19.72% on small-area cells and a record aperture efficiency of 15.86% on modules with an area of 42.9 cm2. This work provides a simple way to scale up high-efficiency flexible perovskite modules for various applications.