11.4% Efficiency Kesterite Solar Cells on Transparent Electrode

Abstract

Thin film solar cells on semitransparent substrates are attracting much attention due to new application scenarios including building‐integrated photovoltaics (BIPV). Environmentally‐benign element constituted and highly stable kesterite Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cells are ideal candidates for such applications. However, the efficiency of kesterite solar cells on semitransparent substrates is far behind that on opaque Mo‐based substrates. Here, fabrication of CZTSSe solar cells on fluorine‐doped tin oxide (FTO) substrates from molecular solution and how step‐by‐step absorber engineering improves device performance is reported. A power conversion efficiency of 7.02% is obtained when the absorber is fabricated on bare FTO, which is improved to 9.56% after adding a MoO3 interfacial layer. Investigations show the enhancement originates from the transformation of MoO3 to MoSe2 during film selenization which initiates crystallization at the back contact and at the same time prevents oversize grains at the absorber surface. Na‐doping and Ag alloying further facilitate grain growth and mitigate band tailing, resulting in a certified effective area efficiency of 11.43% with all device parameters comparable to that on an Mo‐substrate. This is the first time highly efficient kesterite solar cells are demonstrated on transparent electrodes, which opens up new opportunities for these earth‐abundant elements composed of thin film photovoltaics.

Controllable Double Gradient Bandgap Strategy Enables High Efficiency Solution‐Processed Kesterite Solar Cells

“…Also, the bandgap fluctuation caused by charge compensation can lead to small mobility, and the smaller bandgap fluctuations and electrostatic potential fluctuations of the K 2 S device are favorable for carrier mobility. [ 56 ]…”

Back Contact Plasma Treatment Enables 14.5% Efficient Solution‐Processed CuIn(S,Se)2 Solar Cells

“…The existence of MoO 3‐x and MoO 3 is expected to reduce the thickness of MoSe 2 due to their lower chemical reactivity than Mo, which could reduce back contact resistance. [ 28 ] At the same time, O‐rich surface may change the interaction between the precursor solution and the substrate and thus affects property of the precursor film.…”

A critical review of solution-process engineering for kesterite thin-film solar cells: current strategies and prospects

“…The transformation of MoO 3 into MoSe 2 during the grain growth process of the CZTSSe absorption layer helps improve the back contact and enhance the quality of the absorption layer film. Na doping and Ag alloying further promote grain growth and reduce band tail states, resulting in a device efficiency of 11.43%, 103 as shown in Fig. 8c.…”