Abstract
A hole transport layer (HTL) composed of spiro-OMeTAD as a hole transport material (HTM) in a perovskite solar cell (PSC) with CH3NH3PbI3 as a light-absorber was characterized by observing the performance of the cell with variation of the condition in HTL and correlating the result with the electronic structure of the layers, through which positive holes are transferred. While the time-dependent in- crease in the work function of the Au anode, the doping of a spiro-OMeTAD layer with Li-TFSI and tBP, and the light irradiation increased the short-circuit current and the open-circuit voltage, they made the Fermi level of the HTL deeper and closer to the HOMO level of the spiro-OMeTAD layer. Namely, the changes in the performances and the electronic structures are in accord with each other to indicate that the transport of positive holes in the spiro-OMeTAD layer was disturbed by positive hole traps in the layer, and could be improved by the changes in the condition of the layer, which decreased the depth and density of positive hole traps. It is noted that the Fermi level of the HTL with high performance should be much lower than that of the systems in equilibrium with ambient atmosphere, providing a problem to be solved for the stabilization of PSC.
https://ror.org/035kpke84 
