α-CsPbBr3 Perovskite Quantum Dots for Application in Semi-Transparent Photovoltaics.

As effective light absorber 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 firstly develop a simple yet efficient post-treatment 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 property of solid QD film are also improved. Therefore, simultaneously improved open-circuit-voltage (Voc), short-circuit current density (Jsc) and fill factor (FF) were obtained in the corresponding CsPbBr3 QD devices. Finally, the QD solar cells based on optimal hole-transporting layers delivered a highest efficiency exceeding 5% together with an ultrahigh Voc 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.