Enhanced performance of CH3NH3PbI3 perovskite solar cells via interface modification using phenyl ammonium iodide derivatives

Interface modification in perovskite solar cells is a key factor for achieving high power conversion efficiency by suppressing electron-hole recombination and accelerating charge carrier extraction. Here, we use a series of phenyl ammonium derivatives, phenyl ammonium iodide (PAI), benzyl ammonium iodide (BAI), and phenyl ethyl ammonium iodide (PEAI), to modify the interface between methylammonium lead triiodide (MAPbI3) perovskite and Spiro-OMeTAD as a hole transport layer in solar cell devices. The structural and optical properties of the perovskite films are studied and the results reveal the formation of two-dimensional perovskite interfacial layers on the surface of the MAPbI3 film modified with PEAI and BAI whereas the MAPbI3 layer modified with PAI gives an interface layer with slightly different properties compared to the two-dimensional perovskite. Impedance spectroscopy shows that the charge transport resistance of the interface engineered solar cells decreases when compared to pristine MAPbI3. In addition, slower open-circuit voltage decay and longer carrier lifetime are also observed for the modified cells which in total lead to the improvement of the photovoltaic performance. The investigation therefore gives insight in the effect of interface modifications, and especially how different sizes of the molecular interface modifier results in different interface formation and characteristics.