Tuning perovskite morphology by polymer additive for high efficiency solar cell.

Solution processable planar heterojunction perovskite solar cell is a very promising new technology for low cost renewable energy. One of the most common cell structures is FTO/TiO2/CH3NH3PbI3-xClx/spiro-OMeTAD/Au. The main issues of this type of solar cell are the poor coverage and morphology control of the perovskite CH3NH3PbI3-xClx film on TiO2. For the first time, we demonstrate that the problems can be easily resolved by using a polymer additive in perovskite precursor solution during the film formation process. A 25% increase in power conversion efficiency at a value of 13.2% is achieved by adding 1 wt % of poly(ethylene glycol) in the perovskite layer using a 150 °C processed TiO2 nanoparticle layer. The morphology of this new perovskite was carefully studied by SEM, XRD, and AFM. The results reveal that the additive controls the size and aggregation of perovskite crystals and helps the formation of smooth film over TiO2 completely. Thus, the Voc and Jsc are greatly increased for a high efficiency solar cell. The amount of additive is optimized at 1 wt % due to its insulating characteristics. This research provides a facile way to fabricate a high efficiency perovskite solar cell by the low temperature solution process (<150 °C), which has the advancement of conserving energy over the traditional high temperature sintering TiO2 compact layer device.