Solution‐Processed Semitransparent CZTS Thin‐Film Solar Cells via Cation Substitution and Rapid Thermal Annealing

Abstract

Semitransparent solar cells are able to capitalize on land scarcity in urban environments by co‐opting windows and glass structures as power generators, thereby expanding the capacity of photovoltaics to meet energy needs. To be successful, devices must be efficient, possess good visual transparency, long‐term stability, and low cost. Copper zinc tin sulfide is a promising thin‐film material that consists of earth‐abundant elements. For optical transparency, the usual molybdenum back contact is replaced with a transparent conducting oxide (TCO). However, due to subsequent high‐temperature annealing, the TCO degrades, losing conductivity, or forms a poor interface with CZTS. Lower temperatures mitigate this issue but hinder grain growth in CZTS films. Herein, cadmium substitution and silver and sodium doping are used to aid grain growth and improve film quality at lower annealing temperatures. Thin molybdenum is sputtered on TCO to help improve the interface transition postannealing by conversion to MoS2. Rapid thermal processing is used to minimize high‐temperature exposure time to preserve the TCO. With these methods, a semitransparent device with a front illumination efficiency of 2.96% is demonstrated.

A new approach for alkali incorporation in Cu2ZnSnS4 solar cells

“…The low performance of this parameter can be related to the detrimental double-layer morphology and incomplete grain growth of the kesterite. Although in general the efficiency values are modest, they are above the average value of efficiencies reported for kesterite solar cells on transparent or semi-transparent substrates [26,[48][49][50]. It can be seen that Na-doping with an intermediate PDA temperature of 300 • C gathers the best PV parameters, reaching an efficiency of 3%.…”

A Critical Review on the Progress of Kesterite Solar Cells: Current Strategies and Insights

“…The lower annealing temperature is realized because Ag participation assists in grain growth at low temperatures. [91] Nevertheless, it is not feasible to introduce more Ag since a large amount of Ag will diminish the p-type doping density and even result in n-type conductivity. [92] Some recent works also report localized Ag incorporation for surface-type inversion, [30,38] which will be discussed in detail in Section 3.3.…”

11.4% Efficiency Kesterite Solar Cells on Transparent Electrode

“…[ 9 ] in 2012 with the CZTS absorber fabricated on fluorine‐doped tin oxide (FTO)‐coated glass by successive ionic layer adsorption and reaction. Later, a few groups have reported kesterite solar cells on FTO [ 10–17 ] or indium tin oxides (ITO) [ 14–15 ] with the absorbers deposited either by vacuum [ 11–12,14–16 ] or solution methods. [ 13,17 ] For example, Wang et al.…”

“…Later, a few groups have reported kesterite solar cells on FTO [ 10–17 ] or indium tin oxides (ITO) [ 14–15 ] with the absorbers deposited either by vacuum [ 11–12,14–16 ] or solution methods. [ 13,17 ] For example, Wang et al. [ 10 ] reported 4.73% CZTS solar cell via coelectrodeposition process.…”