Organic−inorganic halide perovskites have shown great promise as photovoltaic materials that bridge the gap between facile and low-cost fabrication and exceptional solar cell performance. Manipulation of the stoichiometry and chemistry of the precursors is among the main techniques for controlling the structural properties of perovskite layer. Herein we report that when a precursor solution containing excess cation halides (CH 3 NH 3 I) is utilized for perovskite formation, in situ dissociation of cations (CH 3 NH 3 + ) occurs. The excess iodide ions(I − ) mostly participate in the formation of iodoplumbate complexes such as PbI 3 − and PbI 4 2−. It is shown that the released energy from the crystal formation reaction can dissociate the free CH 3 NH 3 I molecules and iodoplumbate complexes into smaller molecules such as CH 3 I and NH 3 . When the I − concentration in the precursor is increased, more complexes are formed and subsequently more dissociations occur. The produced components are mostly trapped in the perovskite crystals and can act as defects.

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In this work, a full surface coverage CH3NH3PbI3 layer is achieved by controlling the growth mechanism of crystals according to the Stranski–Krastanov mode.

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By introducing an in situ synthesized low-crystalline ZnO (LC-ZnO) (amorphous) layer between the cathode and the active layer of PCPDTBT:CdSe solar cell {PCPDTBT: poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta [2,1-b:3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)]}, the device keeps more than 80 and 40 % of its initial lifetime after 180 and 360 days without any encapsulation, respectively. In this regard, 180 days is the highest lifetime achieved for polymer-based solar cells with direct configuration. In addition, the power conversion efficiency (PCE) is improved up to 70 % in the presence of the LC-ZnO interfacial layer. The LC-ZnO layer is synthesized during polymer annealing after solution-deposition of the precursor at a low temperature (140 °C) and a short time. Highly crystalline ZnO (HC-ZnO) nanoparticles are also synthesized and applied as an interfacial layer. The results show that the LC-ZnO is superior to the HC-ZnO in acting as cathode interfacial layer and moisture scavenger because of the high coverage and surface area provided by the in situ synthesis method.