Charge Carrier Lifetime Determination in Graded Absorber Solar Cells Using Time‐Resolved Photoluminescence Simulations and Measurements

Abstract

Thin‐film photovoltaic device efficiencies are limited by carrier recombination, thus understanding recombination mechanisms is critical for performance improvements. Bulk minority carrier lifetime (τ bulk) is a critical parameter for solar cells but is difficult to determine in P–N junction devices, especially for high doping. As doping ≥1016 cm−3 is required for efficient drift‐charge‐carrier‐collection devices, a method for τ bulk determination in doped P–N junction devices is necessary. This work utilizes time‐resolved photoluminescence (TRPL) simulations to quantify bulk and interface recombination properties in highly doped, graded absorber CdSeTe structures. The two methods developed here for τ bulk determination include utilization of an instantaneous lifetime representation to guide TRPL fitting and direct comparison between measured and simulated decays. Simulations verified that both methods are valid for state‐of‐the‐art device architectures which include graded bandgap absorbers, graded doping, and graded lifetimes. Shifts in the dominant recombination mechanism are identified for sufficiently long τ bulk, where front and back interface quality plays a more prominent role. Evaluation of surface recombination velocities and conduction band offset illustrate electro‐optical advantages of a positive conduction band offset and highlight the necessity of improved interfaces as bulk quality in photovoltaic devices improves.

Synergistic Enhancement of Stability and Performance for Perovskite Solar Cells Using Fluorinated Benzoic Acids as Additives

“…This, in turn, extends the electron/hole recombination lifetime, ultimately enhancing the charge transport efficiency. [ 65–67 ]…”

“…This, in turn, extends the electron/hole recombination lifetime, ultimately enhancing the charge transport efficiency. [65][66][67] To study the effect of additives on the trap density of the solar cell devices thus fabricated, dark current measurements are performed. The dark current measurements of perovskite devices with different additives are shown in Figure 4a.…”

Comprehensive Study of Carrier Recombination in High‐Efficiency CdTe Solar Cells Using Transient Photovoltage

“…[25,27,28,37] All those information is embedded in a single TRPL decay data, and deciphering it and extracting accurate carrier lifetimes become difficult for CdTe samples with graded absorber and other layers. [25] The multiexponential decay form often observed in measurements of CdTe film stacks highlights the complexity of the TRPL data, and it is common in the CdTe community to assign τ 1 to the interface or surface recombination and τ 2 to bulk recombination. While multiexponential fitting indeed sheds light on the existence of different recombination processes, it is only valid when the redistribution of charge carrier density in the sample is minimal, and charge extraction is negligible.…”

“…It is worth mentioning that, in an ideal case where a TRPL setup is able to detect five or even higher orders of magnitude change in signal at a much lower repetition rate (<100 KHz), TRPL decay can also be influenced by the reinjection of the carriers, from electrodes to absorber, and by the detrapping of the carriers from shallow defects. [25,27,28,37] All those information is embedded in a single TRPL decay data, and deciphering it and extracting accurate carrier lifetimes become difficult for CdTe samples with graded absorber and other layers. [25] The multiexponential decay form often observed in measurements of CdTe film stacks highlights the complexity of the TRPL data, and it is common in the CdTe community to assign τ 1 to the interface or surface recombination and τ 2 to bulk recombination.…”

“…This leads to υ = 284 cm s À1 , if surface recombination is the dominant one, which is significantly lower than the values (υ > 1000 cm s À1 ) often used in simulation. [5,10,25,27] TPV technique can, therefore, be applied as a diagnostic tool. As V OC exceeds 850 mV, the radiative recombination process starts to play a role showing a decrease in effective carrier lifetime τ eff .…”