High performance wide bandgap Lead-free perovskite solar cells by monolayer engineering

2PACz monolayer on PEDOT-PSS as the hole transport layer (HTL) was introduced to the inverted p-i-n Tin (Sn) based perovskite solar cells (PSCs) with 1.62 eV bandgap (Wide bandgap). 2PACz giving high efficiency to Pb perovskite solar cells was not effective at all for the Sn perovskite solar cells. We found that the efficiency was enhanced by synergistic effects of the 2PACz monolayer and PEDPT-PSS. The efficiency enhancement was explained by the compactness of the perovskite layer fabricated on bilayer consisting of 2PACz monolayer on PEDOT-PSS, an energetically aligned interface of the HTL/Sn-based perovskite absorber, the lower lattice disordering and reduced non-radiative recombination of the perovskite layer. The cell stability was improved by the compact surface morphology of the Sn perovskite fabricated on bilayer consisting of 2PACz monolayer on PEDOT-PSS and the suppression of direct contact between PEDOT-PSS and perovskite film. EDA0.01(GA0.06(FA0.8Cs0.2)0.94)0.98SnI2Br perovskite fabricated on bilayer consisting of 2PACz monolayer on PEDOT-PSS, gave the power conversion efficiency (PCE) of 8.66%, which is the highest performance for wide bandgap Sn perovskite solar cells reported so far.