An Excellent Modifier: Carbon Quantum Dots for Highly Efficient Carbon‐Electrode‐Based Methylammonium Lead Iodide Solar Cells

Low‐temperature paintable carbon‐electrode‐based perovskite solar cells (LC‐PSCs) are developed predominantly due to several significant advantages of carbon electrodes: they do not require a hole transport layer (HTL) and are low‐cost, easy to fabricate on a large scale, and possess high ambient stability. The most critical hindrance to the photovoltaic performance of LC‐PSCs is the inferior contact between the perovskite and carbon layers. Herein, carbon quantum dots (CQDs) as interface modifiers between the perovskite layer and carbon electrode are applied, which can facilitate hole injection into the carbon electrode, thus improving the photovoltaic performance of LC‐PSCs. Meanwhile, the crystalline properties and hole mobility of the perovskite layer are improved significantly, and defect states in the perovskite layer are passivated following the embedding of CQDs. Finally, a champion efficiency of 13.3% in LC‐PSCs based on perovskite‐CQDs hybrid films without HTL is achieved for an active area of 1 cm2, which represents a 24.3% improvement over the pristine device. Furthermore, LC‐PSC devices maintain more than 95% of their initial efficiency under demanding conditions (humidity >40%, 1000 h). This work opens up a promising pathway to improve the photovoltaic performance of LC‐PSCs and potentially also of other thin‐film solar cells. Crystalline quality of perovskite films is improved due to the additional nucleation sites provided by carbon quantum dots (CQDs) and the interaction of the pyrrolic N in ligands of CQDs with CH3NH3PbI3 (MAPI). This technique opens up a promising pathway to improve the photovoltaic performance of low‐temperature paintable carbon‐electrode‐based perovskite solar cells (LC‐PSCs) and potentially also of other thin‐film solar cells.