Influence of Processing Conditions on the Performance of Cu₂ZnSnS₄ Nanocrystal Solar Cells

Abstract

Quaternary Cu2ZnSnS4 is a promising solar cell material because of its narrow band gap, high light absorption coefficient, and low cost. It is known that the composition of Cu2ZnSnS4 largely influences the solar cell performance. Here, to study the composition dependent properties of Cu2ZnSnS4 NCs as a solar cell material, we synthesized oleylamine‐capped Cu2ZnSnS4 NCs with different compositions by a one‐pot solution process, and fabricated solar cells with a ITO/ZnO/CdS/Cu2ZnSnS4/Au structure, and photoelectrochemical cells. A photovoltaic device using Cu2ZnSnS4 NCs with Cu/ (Zn + Sn)=0.87 showed the best performance among the devices tested. To improve the performance, the NC film fabrication processes were modified. We found that ligand stripping with BF3:OEt2 and the subsequent annealing at 250 °C in N2 improved the power conversion efficiency from 0.06 to 0.14 %, most likely due to efficient stripping of surface insulating organic layers. The photocurrent response of a photoelectrochemical cell using the Cu2ZnSnS4 NCs deposited on a ITO substrate was also improved by the modified NC film fabrication processes.

Effective Ligand Engineering of the Cu2ZnSnS4 Nanocrystal Surface for Increasing Hole Transport Efficiency in Perovskite Solar Cells

“…The solar cell based on CZTS‐OAm NCs without any high‐temperature annealing showed no photocurrent in the device architecture of ITO/CZTS/CdS/Al (Figure S1, Supporting Information). In contrast, the device based on CZTS‐LF showed a short circuit current density ( J sc ) of 1.2 mA cm −2 which actually even exceeds previous report for low‐temperature processed CZTS NCs solar cells (see Figure S1, Supporting Information).…”

Synthesis of Cu2O/CuO Nanocrystals and Their Application to H2S Sensing

“…Thus, the removal of capping agents is necessary for device applications of NCs that are synthesized using the present method. Several routes have been developed for stripping of capping agents from the NC surface [41,42,43,44]. Here, we attempted to remove surface-adsorbed oleylamine by a simple heat treatment at a relatively lower temperature.…”

Controlling Morphology in Polycrystalline Films by Nucleation and Growth from Metastable Nanocrystals

“…Meanwhile, polycrystalline films from nanocrystals of complex copper chalcogenides have typically required aggressive annealing conditions, including the use of caustic selenium/sulfur vapor, to facilitate grain growth. Even with these extreme annealing conditions, the resulting polycrystalline films contain irregular grains not optimal for high-performance solar cells. − CZTS nanorods prepared in a metastable phase (i.e., wurtzite) have been shown to undergo a metastable-to-stable phase transition during annealing in a thin film, with the tantalizing result being a polycrystalline CZTS thin film with uniform and sizable (∼0.3 μm) grains . Here, we show that this phase transformation proceeds by nucleation and growth of the stable kesterite phase, with grain growth propagating from one nanocrystal to the next within a film.…”

“…For the CZTS materials system in particular, current strategies to drive crystallization and grain growth involve annealing in the presence of supplemental elements (Se, S, Na, etc. ), which inevitably couples the grain growth process with compositional changes due to ion exchange or doping. ,,,,− Alternatively, metastable CZTS nanocrystals can be used to achieve significant grain growth at lower temperatures after short, few-second annealing times due to a thermodynamically favorable wurtzite to kesterite phase transformation . While previous reports have examined the influence of precursor or additional processing, such as annealing and selenization/sulfurization under Se/S vapor pressure, ,− on final grain structure, here we sought to understand the underlying grain growth mechanisms for thin films generated from wurtzite CZTS nanocrystals. ,, The apparent nucleation-and-growth mechanism suggests new strategies for tuning the morphology of polycrystalline films derived from nanocrystals.…”