Impact of the Cd²⁺ treatment on the electrical properties of Cu₂ZnSnSe₄ and Cu(In,Ga)Se₂ solar cells

Abstract

The present contribution aims at determining the impact of modifying the properties of the absorber/buffer layer interface on the electrical performance of Cu2ZnSnSe4 (CZTSe) thin‐film solar cells, by using a Cd2+ partial electrolyte (Cd PE) treatment of the absorber before the buffer layer deposition. In this work, CZTSe/CdS solar cells with and without Cd PE treatment were compared with their respective Cu(In,Ga)Se2 (CIGSe)/CdS references. The Cd PE treatment was performed in a chemical bath for 7 min at 70 °C using a basic solution of cadmium acetate. X‐ray photoemission spectroscopy measurements have revealed the presence of Cd at the absorber surface after the treatment. The solar cells were characterized using current density–voltage (J–V), external quantum efficiency, and drive‐level capacitance profiling measurements. For the CZTSe‐based devices, the fill factor increased from 57.7% to 64.0% when using the Cd PE treatment, leading to the improvement of the efficiency (η) from 8.3% to 9.0% for the best solar cells. Similar observations were made on the CIGSe solar cell reference. This effect comes from a considerable reduction of the series resistance (RS) of the dark and light J–V, as determined using the one‐diode model. The crossover effect between dark and light J–V curves is also significantly reduced by Cd PE treatment. Copyright © 2015 John Wiley & Sons, Ltd.

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.…”

“…Second, TRPL data are commonly reported from measurements on completed kesterite devices, [5][6][7][8][9][10][11][12][16][17][18]24] despite the significant effect that charge-carrier separation in an electric field has on PL decays. [2,4,30,31,37] A more concerning observation is that no difference between PL decays measured on absorbers and measured on devices is characterized for kesterites, as seen in Figure 2 where measurements on absorbers and devices are distinguished, and also reported for high-efficiency kesterite devices/ absorbers [25] and devices/absorbers reported here (Section 2.2).…”

“…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 .…”

CuInSe2 thin film solar cells prepared by low-cost electrodeposition techniques from a non-aqueous bath

“…This may be due to the defect states present in the absorber or at the hetero-interface or in the CdS layer[31][32][33][34] . Three dotted circular rings correspond to (112), (204)/(220) and (312)/(116) planes of CIS are observed is selected area diffraction pattern.…”