Perovskite is a promising light harvester for use in photovoltaic solar cells. In recent years, the power conversion efficiency of perovskite solar cells has been dramatically increased, making them a competitive source of renewable energy.

This work will discuss several topics related to perovskite based solar cells: 

Micron sized grains in planar hole conductor free perovskite based solar cells, In this work we demonstrate the planar configuration on HTM free perovskite based solar cells. The CH3NH3PbI3 perovskite was deposited using the spray technique to achieve micron size perovskite crystals. The number of spray passes changes the CH3NH3PbI3 film thickness; for example, 10 spray passes achieved a film thickness of 3.4m of perovskite. Surprisingly, power conversion efficiency of 6.9% was demonstrated for this novel, simple solar cell structure with thick perovskite film that has no HTM. Capacitance-voltage measurements reveal charge accumulation at the CH3NH3PbI3/Au interface while the compact TiO2/CH3NH3PbI3 junction showed a space charge region, which inhibits the recombination.  

High Voltage hole conductor free perovksite solar cells. In this work we demonstrate high open circuit voltage of 1.35V using Al2O3/CH3NH3PbBr3 perovskite solar cells without a hole conductor. The contact potential difference under light measured by surface photovoltage spectroscopy for CH3NH3PbBr3 was more than twice than that for CH3NH3PbI3, which results with smaller surface potential for the Al2O3/CH3NH3PbBr3 cells. Incident modulated photovoltage spectroscopy shows a longer recombination lifetime for the Al2O3/CH3NH3PbBr3 cells than for the TiO2/CH3NH3PbI3 cells or for the TiO2/CH3NH3PbBr3 cells, further supporting the high open circuit voltage. The possibility to gain high open circuit voltage even without a hole transport material in perovskite solar cells shows that the perovskite/metal oxide interface has a major effect on the open circuit voltage in perovskite based solar cells.

Kelvin probe force microscopy is used to measure cross-sections of hole conductor free CH3NH3PbI3 perovskite solar cells. A depletion region width of about 45 nm was determined from the measured potential profiles at the interface between CH3NH3PbI3 and nanocrystalline TiO2, whereas a negligible depletion was measured at the CH3NH3PbI3/Al2O3 interface. A complete solar cell can be realized with the CH3NH3PbI3 that functions both as light harvester and hole conductor in combination with a metal oxide. The band diagrams were estimated from the measured potential profile at the interfaces, and are critical findings for a better understanding and further improvement of perovskite based solar cells.