Recent progress of graphene‐based materials for efficient charge transfer and device performance stability in perovskite solar cells

Two organolead halide perovskite nanocrystals, CH(3)NH(3)PbBr(3) and CH(3)NH(3)PbI(3), were found to efficiently sensitize TiO(2) for visible-light conversion in photoelectrochemical cells. When self-assembled on mesoporous TiO(2) films, the nanocrystalline perovskites exhibit strong band-gap absorptions as semiconductors. The CH(3)NH(3)PbI(3)-based photocell with spectral sensitivity of up to 800 nm yielded a solar energy conversion efficiency of 3.8%. The CH(3)NH(3)PbBr(3)-based cell showed a high photovoltage of 0.96 V with an external quantum conversion efficiency of 65%.

Advancing perovskite solar cell technologies toward their theoretical power conversion efficiency (PCE) requires delicate control over the carrier dynamics throughout the entire device. By controlling the formation of the perovskite layer and careful choices of other materials, we suppressed carrier recombination in the absorber, facilitated carrier injection into the carrier transport layers, and maintained good carrier extraction at the electrodes. When measured via reverse bias scan, cell PCE is typically boosted to 16.6% on average, with the highest efficiency of ~19.3% in a planar geometry without antireflective coating. The fabrication of our perovskite solar cells was conducted in air and from solution at low temperatures, which should simplify manufacturing of large-area perovskite devices that are inexpensive and perform at high levels. Copyright © 2014, American Association for the Advancement of Science.

Perovskite solar cells (PSC) with efficiencies >20% have only been realized with highly expensive organic hole-transporting materials. We demonstrate PSCs achieving stabilized efficiencies exceeding 20% with CuSCN as hole extraction layer using fast solvent removal method to create compact, highly conformal CuSCN layers that facilitate fast carrier extraction and collection. The PSCs showed high thermal stability under long term heating, however, their operational stability was poor. This instability originates from potential induced degradation of the CuSCN/Au contact. The addition of a conductive reduced graphene oxide spacer layer between CuSCN and gold allowed PSCs to retain >95% of their initial efficiency after aging at a maximum power point for 1000 hours at 60 Celsius. Importantly, under both continuous full-sun illumination and thermal stress, CuSCN based devices surpassed the stability of spiro-OMeTAD based PSCs.