Building integration of perovskite solar cells could 1 day become feasible because of their low cost, aesthetics, lightweight, and impressive power conversion efficiency (PCE). [1][2][3][4][5] When focusing on potential substrate materials compatible with the building industry, coated steel offers an interesting perspective because it is one of the most common architectural materials, especially in industrial buildings. Steel is a cheap (substrate) material and offers excellent mechanical, heat resistance, and barrier properties against oxygen and humidity. [6,7] Combining perovskite solar cells with steel can give added value to this commonly employed building material. One of the challenges to tackle when fabricating solar cells directly on steel substrates is the higher surface roughness as compared to glass or polymer film which can be fatal for thin-film solar cells. Using smooth steel substrates would add to the cost due to the extra surface polishing steps. The cost can be reduced when combining rough steel substrates with an additional planarization layer. [8] Fabricating perovskite solar cells on rough substrates may reduce device performance and yield, due to irregularities such as spike-like protrusions, valleys, and peaks. To investigate the impact of surface roughness on the photovoltaic performance, we developed a substrate-configuration n-i-p solar cell for coated steel substrates (Figure 1). Fabrication of perovskite solar cells on rough substrates has been mostly studied in superstrateconfiguration single-junction and top-illuminated perovskite Si monolithic tandem solar cells. [9][10][11][12][13][14][15] In several studies on tandem solar cell applications a rough pyramidal-textured Si substrate has been used. To achieve a conformal coverage of the perovskite active layer, the perovskite layer needs to be sufficiently thick, or it needs to be deposited via co-evaporation [9][10][11] or a hybrid evaporation/spin coating deposition method. [12][13][14] Tockhorn et al. demonstrated conformal coating of the perovskite active layer in single-junction superstrate-configuration perovskite solar cells by employing a self-assembled [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) monolayer hole transport layer (HTL) on a nanotextured indium tin oxide (ITO) glass substrate providing 19.7% efficiency. [15] In substrate-configuration perovskite solar cells, most devices have been fabricated on polished Ti foils, reaching efficiencies up to 15%. [16] Although most studies on substrate-configuration perovskite solar cells use polished Ti