Improved photovoltaic performances of lead-free Cs2AgBiBr6 perovskite solar cells incorporating tetracene as co-hole transport layer

Cs2AgBiBr6 double perovskite compounds have been increasingly studied in recent years as promising candidates able to counter polluting, harmful and oxygen/moisture sensitive issues intrinsic to traditional lead-containing solar cells. Exhibiting high optical absorption coefficient, low toxicity and important structural stability, Cs2AgBiBr6 solar cells still suffer from limited absorption of low energy photons, low carrier mobility, and limited carrier lifetimes induced by defect states. Herein, for the first time, a molecular layer of tetracene has been introduced within a Cs2AgBiBr6-based photovoltaic architecture: being incorporated at the interface between the double perovskite photoabsorber and Spiro-OMeTAD hole transport material, tetracene allows for a suitably graded cascade of energy bands within the solar cell architecture, which ultimately improves interfacial charge transfers and reduces charge recombinations. The performances in photovoltaic devices are consequently enhanced vs. tetracene-free configurations, with champion values of open circuit voltages of 1.1 V (vs. 1.0 V), current densities of 2.5 mA/cm² (vs. 1.9 mA/cm²) and photoconversion efficiencies of 1.7% (vs. 1.3%) with reduced hysteretic behavior.