Understanding Temperature‐Dependent Charge Extraction and Trapping in Perovskite Solar Cells

Abstract

Understanding the factors that limit the performance of perovskite solar cells (PSCs) can be enriched by detailed temperature (T)-dependent studies. Based on p-i-n type PSCs with prototype methylammonium lead triiodide (MAPbI 3 ) perovskite absorbers, T-dependent photovoltaic properties are explored and negative T-coefficients for the three device parameters (V OC , J SC , and FF) are observed within a wide low T-range, leading to a maximum power conversion efficiency (PCE) of 21.4% with an impressive fill factor (FF) approaching 82% at 220 K. These T-behaviors are explained by the enhanced interfacial charge transfer, reduced charge trapping with suppressed nonradiative recombination and narrowed optical bandgap at lower T. By comparing the T-dependent device behaviors based on MAPbI 3 devices containing a PASP passivation layer, enhanced PCE at room temperature is observed but different tendencies showing attenuating T-dependencies of J SC and FF, which eventually leads to nearly T-invariable PCEs. These results indicate that charge extraction with the utilized all-organic charge transporting layers is not a limiting factor for low-T device operation, meanwhile the trap passivation layer of choice can play a role in the T-dependent photovoltaic properties and thus needs to be considered for PSCs operating in a temperature-variable environment.

Low-Temperature Induced Enhancement of Photoelectric Performance in Semiconducting Nanomaterials

“…Taskensen et al also witnessed the simultaneous improvement of V OC and fill factor (FF) on CZTSe solar cells during cooling to 240 K [ 163 ]. As illustrated in Figure 7 b, both the FF and PCE of hybrid perovskite solar cells significantly increase with declining temperature [ 164 ]. Temperature-dependent photovoltaic properties are closely related to light absorption, the motion of photogenerated carriers and even the structure and composition of devices.…”

“…Chen et al studied cooling-caused variations in MAPbBr 3 solar cells and proposed the insulating nature of a charge-extraction layer, rather than an absorption layer restricting performance at low temperature [ 174 ]. Represented by Figure 7 e, the PL intensity of the charge-transporting layer is lowered compared to control samples at various temperatures, implying a more efficient charge transfer in interfaces, especially at low temperature [ 164 ]. Nevertheless, Shao et al observed that deteriorated charge-carrier extraction caused a PCE drop at low temperature when using [ 60 ] PCBM as an electron extraction layer [ 103 ].…”

“…The rates of trapping declined from ~10 −8 cm 3 s −1 at room temperature to ~10 −9 cm 3 s −1 at low temperature due to less phonon-mediated recombination. Another experiment by Zhou et al claimed the impact of surface passivation by PASP benefiting the reduction of trap states during temperature-dependent measurements [ 164 ]. The temperature dependence of charge-carrier recombination opens up a new mechanism for improving perovskite solar cells’ output.…”

“…( a ) Temperature-dependent V OC of CZTS-based solar cells (adapted from [ 57 ], with permission from Wiley-VCH, 2018). ( b ) Cooling-enhanced PCE and FF of perovskite solar cells (adapted from [ 164 ], with permission from Wiley-VCH, 2019). ( c ) Phase transition (adapted from [ 39 ], with permission from Wiley-VCH, 2019).…”

“…( e ) Charge extraction. ( f ) Charge trapping (adapted from [ 164 ], with permission from Wiley-VCH, 2019). ( g ) Recombination rate (adapted from [ 30 ], with permission from Wiley-VCH, 2015).…”