Indications of short minority-carrier lifetime in kesterite solar cells

Abstract

Solar cells based on kesterite absorbers consistently show lower voltages than those based on chalcopyrites with the same bandgap. We use three different experimental methods and associated data analysis to determine minority-carrier lifetime in a 9.4%-efficient Cu 2 ZnSnSe 4 device. The methods are cross-sectional electron-beam induced current, quantum efficiency, and time-resolved photoluminescence. These methods independently indicate minority-carrier lifetimes of a few nanoseconds. A comparison of current-voltage measurements and device modeling suggests that these short minority-carrier lifetimes cause a significant limitation on the voltage produced by the device. The comparison also implies that low minority-carrier lifetime alone does not account for all voltage loss in these devices. V C 2013 AIP Publishing LLC. [http://dx.

Identifying the Real Minority Carrier Lifetime in Nonideal Semiconductors: A Case Study of Kesterite Materials

“…First, no correlation between the measured PL decay times and device performance over a wide range (1%-12%) of device efficiencies (shown in Figure 2) and open-circuit voltage V OC (see the Supporting Information) can be found from published TRPL data. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] These results are in contrast to that found from TRPL analysis of chalcopyrites and CdTe where a correlation with device efficiency and V OC is clear, as τ n is a measure of recombination losses. [33][34][35][36] However, for kesterites the connection between PL decay time and the assumed τ n is not apparent, as the reported decay times represent arbitrary measurement excitation conditions and data analysis procedures; characteristic decay times from a variety of fitting regions and techniques are reported for measured TRPL data.…”

“…Additionally, TRPL data measured on kesterites are typically reported with poor signal-to-noise ratio, with PL decays generally resolved over 1-3 orders of magnitude of signal decay. [5][6][7][9][10][11][12]14,15,18,[20][21][22][23][24] As various transport mechanisms can occur within this decay range care must be taken in interpreting such signal.…”

“…Similar conclusions were observed by Repins et al following device simulation. [22] Device simulation and experimental results in chalcopyrites and CdTe demonstrate that sub-nanosecond minority carrier lifetimes are sufficient to achieve power conversion efficiencies (PCE) up to ≈13%, [34,40] representing the performance level currently reported for kesterites. [41] In this work, we analyze intensity-, temperature-, voltagedependent, and spectrally resolved TRPL data measured on CZTSe and CZTSSe absorbers and devices to determine the origin of the PL decay signal.…”

“…Data are taken from refs. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. The solid lines represent device simulation results bounded by S F = 10 2 -10 6 cm s −1 and S B = 10 2 -10 7 cm s −1 ; the dashed line represents a lower bound on the efficiency for a reduced mobility gap E µ = E PL,Peak .…”

Analysis of Failure Modes in Kesterite Solar Cells

“…77 draw an opposite conclusion and incriminate the low mobility. Other studies 41 quantify losses due to low carrier lifetime ("30-50 mV in VOC and 2-4% absolute in efficiciency"). Another debated point in literature concerns the responsibility of interface recombination in VOC deficit.…”