Effective Improvement of the Photovoltaic Performance of Carbon-Based Perovskite Solar Cells by Additional Solvents

During the past 5 years, there has been a surging interest in the study of organic–inorganic hybrid perovskite compounds for applications in photovoltaic devices because of low cost, simple fabrication process, and high-efficiency solar power conversion [ 1 – 6 ]. Typically, perovskite solar cells (PSCs) employed a mesoporous titania or alumina scaffold, a methylammonium (MA) lead iodide perovskite light absorber, an organic hole transport material (HTM), characteristically spiro-OMeTAD (2,2′,7,7′-tetrakis-( N , N -di- p -methoxyphenylamine)-9,9′-bifluorene), and an Au or Ag electrode. PSCs achieved a power conversion efficiency (PCE) of >10 % in 2012 [ 2 , 3 ]. TiO 2 /spiro-OMeTAD is regarded as a successful couple owing to its good optical transparency and perfect band alignment with respect to CH 3 NH 3 PbI 3 . Later, the PCEs were improved to 15 % using a two-step sequential deposition technique, involving spin-coating of a PbI 2 followed by exposure to a solution of CH 3 NH 3 I to form CH 3 NH 3 PbI 3 , or a dual-source vapor deposition technique to fabricate a planar heterojunction solar cell [ 4 , 5 ]. Then, a planar structured PSC using a polyethyleneimine ethoxylated modified ITO electrode, yttrium-doped TiO 2 layer, mixed halide perovskite CH 3 NH 3 PbI 3− x Cl x absorber, and spiro-OMeTAD reached a PCE of 19.3 % [ 6 ]. Very recently, triple Cs/MA/formamidinium cation PSCs reached a power output of 21.1 % [ 7 ].