α-CsPbBr₃ Perovskite Quantum Dots for Application in Semitransparent Photovoltaics

As effective light absorbers in solar cells, CsPbI₃ all-inorganic perovskite quantum dots (QDs) have received increasing attention, benefitting from their suitable optical band gap and thermal stability. However, the easy cubic to yellow orthorhombic phase transition hinders their further application in stable photovoltaic devices. CsPbBr₃ QDs have been targeted as a promising material for ultrahigh voltage and stable solar cells. In this work, we first develop a simple yet efficient post-treatment method using guanidinium thiocyanate (GASCN), which is able to exchange the native capping ligands of CsPbBr₃ QDs, thus improving the carrier transport properties through enhanced electrical coupling between QDs. Additionally, the morphology and crystalline properties of solid QD films are also improved. Therefore, simultaneously improved open-circuit voltage (V_oc), short-circuit current density (J_sc), and fill factor (FF) were obtained in the corresponding CsPbBr₃ QD devices. Finally, the QD solar cells based on optimal hole-transporting layers delivered the highest efficiency exceeding 5% together with an ultrahigh V_oc of 1.65 V, representing the most efficient CsPbBr₃ QD solar cells to date. More importantly, the CsPbBr₃ perovskite QD solar cells developed here exhibit excellent stability, ultrahigh voltage, and high transparency over the entire visible spectrum region, demonstrating their great potential in applications like solar windows of greenhouse and hydrogen generation driven by perovskite solar cells.