TY  - JOUR
A1  - Stolterfoht, Martin
A1  - Wolff, Christian Michael
A1  - Amir, Yohai
A1  - Paulke, Andreas
A1  - Perdigon-Toro, Lorena
A1  - Caprioglio, Pietro
A1  - Neher, Dieter
T1  - Approaching the fill factor Shockley-Queisser limit in stable, dopant-free triple cation perovskite solar cells
JF  - Energy & Environmental Science
N2  - 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.
Y1  - 2017
U6  - https://doi.org/10.1039/c7ee00899f
SN  - 1754-5692
SN  - 1754-5706
VL  - 10
SP  - 1530
EP  - 1539
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Stolterfoht, Martin
A1  - Caprioglio, Pietro
A1  - Wolff, Christian Michael
A1  - Marquez, Jose A.
A1  - Nordmann, Joleik
A1  - Zhang, Shanshan
A1  - Rothhardt, Daniel
A1  - Hörmann, Ulrich
A1  - Amir, Yohai
A1  - Redinger, Alex
A1  - Kegelmann, Lukas
A1  - Zu, Fengshuo
A1  - Albrecht, Steve
A1  - Koch, Norbert
A1  - Kirchartz, Thomas
A1  - Saliba, Michael
A1  - Unold, Thomas
A1  - Neher, Dieter
T1  - The impact of energy alignment and interfacial recombination on the internal and external open-circuit voltage of perovskite solar cells
JF  - Energy & environmental science
N2  - Charge transport layers (CTLs) are key components of diffusion controlled perovskite solar cells, however, they can induce additional non-radiative recombination pathways which limit the open circuit voltage (V-OC) of the cell. In order to realize the full thermodynamic potential of the perovskite absorber, both the electron and hole transport layer (ETL/HTL) need to be as selective as possible. By measuring the photoluminescence yield of perovskite/CTL heterojunctions, we quantify the non-radiative interfacial recombination currents in pin- and nip-type cells including high efficiency devices (21.4%). Our study comprises a wide range of commonly used CTLs, including various hole-transporting polymers, spiro-OMeTAD, metal oxides and fullerenes. We find that all studied CTLs limit the V-OC by inducing an additional non-radiative recombination current that is in most cases substantially larger than the loss in the neat perovskite and that the least-selective interface sets the upper limit for the V-OC of the device. Importantly, the V-OC equals the internal quasi-Fermi level splitting (QFLS) in the absorber layer only in high efficiency cells, while in poor performing devices, the V-OC is substantially lower than the QFLS. Using ultraviolet photoelectron spectroscopy and differential charging capacitance experiments we show that this is due to an energy level mis-alignment at the p-interface. The findings are corroborated by rigorous device simulations which outline important considerations to maximize the V-OC. This work highlights that the challenge to suppress non-radiative recombination losses in perovskite cells on their way to the radiative limit lies in proper energy level alignment and in suppression of defect recombination at the interfaces.
Y1  - 2019
U6  - https://doi.org/10.1039/c9ee02020a
SN  - 1754-5692
SN  - 1754-5706
VL  - 12
IS  - 9
SP  - 2778
EP  - 2788
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  -