Abstract
The charge carrier lifetime is an important parameter in solar cells as it defines, together with the mobility, the diffusion length of the charge carriers, thus directly determining the optimal active layer thickness of a device. Herein, we report on charge carrier lifetime values in bromine doped planar methylammonium lead iodide (MAPbI3) solar cells determined by transient photovoltage. The corresponding charge carrier density has been derived from charge carrier extraction. We found increased lifetime values in solar cells incorporating bromine compared to pure MAPbI3 by a factor of ~2.75 at an illumination intensity corresponding to 1 sun. In the bromine containing solar cells we additionally observe an anomalously high value of extracted charge, which we deduce to originate from mobile ions.
Highlights
carrier extraction (CE) experiments provided an anomalously large signal at longer timescales in the solar cell with the most bromine content, leading to a recombination current Jrec, which is larger than the short circuit current Jsc at 1 sun
All solar cells display a very small hysteresis, the power conversion efficiency (PCE) of forward and backward scans are comparable and show a decent performance with a PCE between 8–13% for all studied devices.The impact of bromine doping is evident in an increased Voc from 0.882 V to 1.113 V which can mainly be assigned to the increased band gap of the bromine containing cells[28]
Whereas the pure MAPbI3 solar cell displays a CE signal which is saturated after 0.1 ms, leading to a Jrec being comparable to Jsc, the device with largest bromine content shows an anomalous behavior
Summary
CE experiments provided an anomalously large signal at longer timescales in the solar cell with the most bromine content, leading to a recombination current Jrec, which is larger than the short circuit current Jsc at 1 sun. By bromine doping of the perovskite absorber, the charge carrier lifetime increases in the studied illumination intensity range: 0.36–72.5 μs for MAPb(I0.71Br0.29)[3] and 0.53–35.02 μs for the MAPb(I0.46Br0.54)[3] device.
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