Highly efficient, ultrathin (~400 nm) pure sulfide kesterite Cu₂ZnSnS₄ (CZTS) solar cells have been realized by interface reaction route controlling and self-organized nano-pattern at the back contact. The Al₂O₃ intermediate layer introduced at the Mo/CZTS interface can effectively inhibit the detrimental interfacial reaction between CZTS and Mo in the initial stage of sulfurization, and then turns into a self-organized nanopattern yielding a nanoscale opening for electrical contact. With this interface modification, the traditional issues of phase segregation (secondary phases) and voids at the back contact region can be well addressed, which greatly improves uniformity and reduces back contact recombination. As a result, this interface modification not only leads to beyond 8% ultrathin CZTS solar cells but also yields two certificated world record efficiencies: 9.26% for 0.237 cm² small area and 7.61% for 1 cm² standard kesterite CZTS solar cells (normal thickness).

A sustainable method for reclaiming silicon (Si) wafers from an end-of-life photovoltaic module is examined in this paper. A thermal process was employed to remove ethylene vinyl acetate and the back-sheet. We found that a ramp-up rate of 15 °C min⁻¹ and an annealing temperature of 480 °C enabled recovery of the undamaged wafer from the module. An ecofriendly process to remove impurities from the cell surface was developed. We also developed an etching process that precludes the use of hydrofluoric (HF) acid. The method for removing impurities consists of three steps: (1) recovery of the silver (Ag) electrode using nitric acid (HNO₃); (2) mechanical removal of the anti-reflecting coating, emitter layer, and p–n junction simultaneously; and (3) removal of the aluminum (Al) electrode using potassium hydroxide (KOH). The reclaimed wafers showed properties that are almost identical to those of commercial virgin wafers: 180 μm average thickness; 0.5 and 3.7 Ω cm minimum and maximum resistivities, respectively; and 1.69 μs average carrier lifetime. In addition, cells fabricated with the reclaimed wafers showed an efficiency equivalent to that of the initial cells.

The ideal approach for disposing of end-of-life photovoltaic (PV) modules is recycling. Since it is expected that more than 50 000 t of PV modules will be worn out in 2015, the recycling approach has received significant attention in the last few years. In order to recover Si wafers from degraded solar cells, metal electrodes, anti-reflection coatings, emitter layers, and p–n junctions have to be removed from the cells. In this study, we employed two different chemical etching processes to recover Si wafers from degraded Si solar cells. Each etching process consisted of two steps: (1) first etching carried out using a nitric acid (HNO₃) and hydrofluoric acid (HF) mixture and potassium hydroxide (KOH), (2) second etching carried out using phosphoric acid (H₃PO₄) and a HNO₃ and HF mixture. The first etching process resulted in deep grooves, 36 μm on average, on the front of recycled wafers that rendered the process unsuitable for wafers to be used in solar cell production. Such grooves occurred due to different etching rates of Ag electrodes and silicon nitride (SiN_x). On the other hands, the second etching process did not result in such grooves and produced a recovered Si wafer with a uniform and smooth surface. The recycled wafers obtained by the second etching process showed properties almost identical to those of commercial virgin wafers: thickness, 173 μm; minimum and maximum resistivity, 1.6 and 10 Ω cm, respectively; and average carrier lifetime, 1.785 μs. In addition, P and Al atoms were not detected in the recycled wafers by secondary ion mass spectroscopy.