N-phenylindole-diketopyrrolopyrrole-containing narrow band-gap materials for dopant-free hole transporting layer of perovskite solar cell

Novel conjugated materials, DPIO and DPIE, having same molecular configuration of both an electron donating N-phenylindole and an electron accepting diketopyrrolopyrrole derivative, exhibited different aggregation behavior because of the applied side chains. When DPIO and DPIE were applied to as hole transporting materials in perovskite solar cell, DPIO showed better device performance than ones with DPIE, mostly due to the aggregation-assisted enhanced electrical property. DPIO effectively extracted hole from the perovskite layer, providing over 10% PCE of cell efficiency without any chemical doping. Incident-photon-to-electron conversion efficiency (IPCE) measurement confirmed that DPIO’s strong absorption in the longer wavelength region partly contributed to the light harvesting of the solar cell device. In addition, time-resolved photoluminescence (TRPL) and transient photovoltage (TPV) studies proved that the DPIO-based device, compared to the conventional Spiro-MeOTAD-based device, has better charge extraction ability and reduced charge recombination.