In the current study, the perovskite absorber (CH3NH3PbI3) is processed via one-step deposition employing the small molecule additive, BmPyPhB, which can be dissolved in dimethylformamide along with precursors. Here, 1,3-Bis[3,5-di(pyridin-3-yl)phenyl]benzene (BmPyPhB) functions as the morphology controller to introduce an intermediate phase during perovskite film growth, which allows well-defined and precrystallized domains formed before the annealing treatment. Furthermore, a chloroform solvent wash procedure is applied afterward to remove BmPyPhB from perovskite without damaging the predetermined morphology. Thus, postannealing as low as 100°C for 5 min can achieve the optimal power conversion efficiency of 8% in a planar-structured inverted solar cell.
Tandem solar cells provide an effective way to harvest a broader spectrum of solar radiation by combining two or more
solar cells with different absorption ranges. However, for polymer solar cells (PSCs), the performance of tandem devices
lags behind single-layer cells mainly due to the lack of a high-performance low-bandgap polymer with appropriate
spectral response range. Here, we demonstrate a novel low bandgap conjugated polymer (~1.44 eV) specifically suitable for tandem structure. In the single-layer device, power conversion efficiency (PCE) of 6.5% was achieved. When the polymer was applied to tandem solar cells, we demonstrated a NREL certified PCE of 8.62%<sup></sup> . Further optimization on materials and devices of this system has lead to record breaking efficiency of 10.6%. Furthermore, the tandem devices show excellent stability due both to the intrinsic stability of the polymer and the advanced device structure.