Carbon based perovskite solar cells (PSCs) are fabricated through easily scalable screen printing techniques, using abundant and cheap carbon to replace the hole transport material (HTM) and the gold electrode further reduces costs, and carbon acts as a moisture repellent that helps in maintaining the stability of the underlying perovskite active layer. An inorganic interlayer of spinel cobaltite oxides (CoO) can greatly enhance the carbon based PSC performance by suppressing charge recombination and extracting holes efficiently. The main focus of this research work is to investigate the effectiveness of CoO spinel oxide as the hole transporting interlayer for carbon based perovskite solar cells (PSCs). In these types of PSCs, the power conversion efficiency (PCE) is restricted by the charge carrier transport and recombination processes at the carbon-perovskite interface. The spinel CoO nanoparticles are synthesized using the chemical precipitation method, and characterized by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and UV-Vis spectroscopy. A screen printed thin layer of p-type inorganic spinel CoO in carbon PSCs provides a better-energy level matching, superior efficiency, and stability. Compared to standard carbon PSCs (PCE of 11.25%) an improved PCE of 13.27% with long-term stability, up to 2500 hours under ambient conditions, is achieved. Finally, the fabrication of a monolithic perovskite module is demonstrated, having an active area of 70 cm and showing a power conversion efficiency of >11% with virtually no hysteresis. This indicates that CoO is a promising interlayer for efficient and stable large area carbon PSCs.

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A fully printable, hole‐conductor‐free perovskite solar cell with a simple and low‐cost fabrication route and high stability is well placed for commercialization. We aim to simplify the fabrication process of these solar cells by replacing the mesoporous TiO2 (meso‐TiO2) layer with a thick ZrO2 layer. This new architecture required only three steps: screen‐printing first the compact TiO2 (c‐TiO2), second the mesoporous ZrO2 layer (for perovskite infiltration), and third the carbon electrode. To improve the solar cell performance of the architecture, the c‐TiO2 and ZrO2 printing process are optimized. After systematic optimization of these processes, we found that the double‐printing of the c‐TiO2 layer and an increase of the ZrO2 later thickness from 1.4 to 2.1 μm in the device structure gives an optimized efficiency of 9.69 %, which is comparable to that of standard carbon devices with meso‐TiO2. This method provides an approach to reduce the fabrication time and thermal budget for fully printable solar cells.