@article{StolterfohtWolffAmiretal.2017,
  author    = {Stolterfoht, Martin and Wolff, Christian Michael and Amir, Yohai and Paulke, Andreas and Perdigon-Toro, Lorena and Caprioglio, Pietro and Neher, Dieter},
  title     = {Approaching the fill factor Shockley-Queisser limit in stable, dopant-free triple cation perovskite solar cells},
  series = {Energy \& Environmental Science},
  volume    = {10},
  journal   = {Energy \& Environmental Science},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {1754-5692},
  doi       = {10.1039/c7ee00899f},
  pages     = {1530 -- 1539},
  year      = {2017},
  abstract  = {Perovskite solar cells now compete with their inorganic counterparts in terms of power conversion efficiency, not least because of their small open-circuit voltage (V-OC) losses. A key to surpass traditional thin-film solar cells is the fill factor (FF). Therefore, more insights into the physical mechanisms that define the bias dependence of the photocurrent are urgently required. In this work, we studied charge extraction and recombination in efficient triple cation perovskite solar cells with undoped organic electron/hole transport layers (ETL/HTL). Using integral time of flight we identify the transit time through the HTL as the key figure of merit for maximizing the fill factor (FF) and efficiency. Complementarily, intensity dependent photocurrent and V-OC measurements elucidate the role of the HTL on the bias dependence of non-radiative and transport-related loss channels. We show that charge transport losses can be completely avoided under certain conditions, yielding devices with FFs of up to 84\%. Optimized cells exhibit power conversion efficiencies of above 20\% for 6 mm(2) sized pixels and 18.9\% for a device area of 1 cm(2). These are record efficiencies for hybrid perovskite devices with dopant-free transport layers, highlighting the potential of this device technology to avoid charge-transport limitations and to approach the Shockley-Queisser limit.},
  language  = {en}
}
@article{WolffZuPaulkeetal.2017,
  author    = {Wolff, Christian Michael and Zu, Fengshuo and Paulke, Andreas and Perdigon-Toro, Lorena and Koch, Norbert and Neher, Dieter},
  title     = {Reduced Interface-Mediated Recombination for High Open-Circuit Voltages in CH3NH3PbI3 Solar Cells},
  series = {Advanced materials},
  volume    = {29},
  journal   = {Advanced materials},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {0935-9648},
  doi       = {10.1002/adma.201700159},
  pages     = {8},
  year      = {2017},
  abstract  = {Perovskite solar cells with all-organic transport layers exhibit efficiencies rivaling their counterparts that employ inorganic transport layers, while avoiding high-temperature processing. Herein, it is investigated how the choice of the fullerene derivative employed in the electron-transporting layer of inverted perovskite cells affects the open-circuit voltage (V-OC). It is shown that nonradiative recombination mediated by the electron-transporting layer is the limiting factor for the V-OC in the cells. By inserting an ultrathin layer of an insulating polymer between the active CH3NH3PbI3 perovskite and the fullerene, an external radiative efficiency of up to 0.3\%, a V-OC as high as 1.16 V, and a power conversion efficiency of 19.4\% are realized. The results show that the reduction of nonradiative recombination due to charge-blocking at the perovskite/organic interface is more important than proper level alignment in the search for ideal selective contacts toward high V-OC and efficiency.},
  language  = {en}
}