Co-evaporation and hybrid approaches for fabrication of MAPbI3 for perovskite solar cells

Manuela Ferrara, Maria Federica Caso, Fausta Loffredo, Giuseppe Nasti, Corinna Ponti, Gennaro V. Sannino, Carmen Serpico, Fulvia Villani, Paola Delli Veneri, Lucia V. Mercaldo

Abstract:

In recent years there is growing interest in thermal evaporation methods in the development of perov-skite solar cells. These techniques offer advantages such as scalability to large areas, high layer uni-formity, low material consumption, conformal coating of the substrate, and the absence of toxic sol-vents. We developed the archetypal methylammonium lead iodide (MAPbI3 or MAPI) via three methods: co-evaporation, a two-step hybrid approach consisting of evaporation of a PbI2 template followed by spin-coating of the MAI solution, and a second hybrid route with the MAI solution applied via inkjet printing on the evaporated PbI2 surface. For the co-deposited films, the temperature of the source, the amount of precursor in the crucible and the chamber pressure were appropriately optimized. In the hy-brid approaches, concentration of MAI solution, thermal annealing conditions, and specific parameters of the two techniques were optimized. Post treatments were additionally tested. The films were charac-terized with X-ray diffraction, scanning electron microscopy, photoluminescence with excitation at 514 nm, UV-vis transmittance, and spectroscopic ellipsometry. The thickness of the MAPI films was kept in the range of 350 – 450 nm. The materials were finally applied as a photoactive layer in n-i-p solar cells with solution-processed SnO2 and Spiro-OMeTAD as electron and hole transport layers, respectively. Functioning devices were produced with all the manufacturing methods. The bandgap of the MAPI ab-sorber, assessed from external quantum efficiency spectra, was ~1.6 eV, and a similar optical response was detected. Electrically, superior results were achieved with co-evaporated films, with conversion efficiency currently up to 14.8%.

 

ViperLab Expertise

Lucia V. MERCALDO

Manuela FERRARA

Paola DELLI VENERI