Rapid and low temperature processing of mesoporous TiO 2 for perovskite solar cells on flexible and rigid substrates. Materials Today Communications, 13, 232-240.

The beneficial effect of surface photoreduction on the photoresponse of copper bismuthate is reported for the first time. A detailed photoemission spectroscopy study (PES) reveals that irradiation of CuBi2O4 with hν ≥ 2.7 eV in an inert atmosphere leads to the formation of reduced surface Cu. Surface states associated with reduced Cu species induce a 0.35 eV downward band bending, which improves the charge carrier transport properties of this material as judged by a measured increase of the characteristic surface photovoltage (SPV) from 0.07 to 0.27 V. In connection with this PES study, improvements of up to 30% in the photoresponse are observed for CuBi2O4 photocathodes that have been subjected to a visible light irradiation (100 mW/cm2 white LED) in argon prior to photoelectrochemical performance testing using H2O2 as an electron scavenger. The stability of reduced surface states and associated SPV under relevant reaction conditions has been further studied by near-ambient pressure PES. Results indicate that reduced surface states remain stable in the presence of Ar and methanol, but reoxidation of surface Cu occurs in the presence of oxygen, which decreases the measured SPV. Hence, this work establishes a direct relationship between the presence of reduced Cu at the surface and SPV of CuBi2O4, having important implications on its photovoltaic properties. A similar downward band bending is observed at the interface between CuBi2O4 and a Cu thin film deposited by physical vapor deposition, which further highlights the importance of the Cu/CuBi2O4 buried interface in photoelectrodes.

To date, substrate‐configuration metal‐halide perovskite solar cells (PSCs) fabricated on opaque substrates such as metal foils provide inferior efficiencies compared with superstrate‐configuration cells on transparent substrates such as glass. Herein, a substrate‐configuration PSC on planarized steel is presented. To quantify the differences between the two configurations, a 15.6%‐efficient n–i–p superstrate‐configuration PSC is transformed step wise into a substrate‐configuration cell. Guided by optical modeling, the opaque Au electrode is replaced by a transparent MoO3/thin Au/polystyrene dielectric–metal–dielectric electrode. The semitransparent device affords efficiencies of 15.4% and 11.4% for bottom and top illumination, respectively. Subsequently, substrate‐configuration PSCs with a metal bottom electrode are fabricated on glass and planarized steel, using a thin MoO3 interlayer between the Au bottom electrode and the SnO2 electron transport layer. The glass‐based substrate‐configuration cell provides 14.0% efficiency with identical open‐circuit voltage and fill factor as the superstrate cell. The cell on planarized steel reaches 11.5% efficiency due to a lower fill factor. For both substrate‐configuration cells, the lower short‐circuit current density limits the efficiency. Optical modeling explains this quantitatively to be due to absorption and reflection by the top electrode and absorption by the organic hole transport layer.

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