Pulsed laser deposition of CZTS thin films, their thermal annealing and integration into n-Si/CZTS photovoltaic devices

Abstract

The pulsed laser deposition (PLD) technique is used for the room-temperature (RT) deposition of Cu <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> ZnSnS <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> (CZTS) films. The PLD-CZTS films were subjected to post-annealing at different temperature ranging from 300–500°C in argon atmosphere. The X-ray diffraction and Raman analyses confirmed that the films crystallize in the kesterite structure regardless of their annealing temperature (Ta), but their crystallite size is found to increase with Ta and reaches its maximum value of 37 nm for Ta=400°C. The corresponding optical bandgap value of the PLD-CZTS films post-annealed at 400°C was found to be 1.6 eV. These PLD-CZTS films were directly integrated into Al/n-Si/PLD-CZTS/Al heterojunction PV devices without resorting to any surface treatment and/or post-sulfurization process. Under standard AM1.5 solar illumination, the Al/n-Si/PLD-CZTS/Al PV devices were found to yield a power conversion efficiency (η) of 1.1%, with a V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</inf> of 0.140 V, a J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</inf> of 26 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and a fill factor of 31%. Even if the obtained η value is still modest, it underlines nonetheless the promising potential of PLD-CZTS films as an effective absorber layer in Si-based heterojunction solar cells.