Influence of alkali iodide fluxes on Cu2ZnSnS4 monograin powder properties and performance of solar cells

<h3>Abstract</h3><p>One promising and cost-effective method to produce flexible solar panels in the future is monograin layer (MGL) solar cell technology based on monograin powder (MGP) crystals. The results of the present study demonstrate the influence of different alkali salts (LiI, NaI, KI, RbI and CsI) on the properties of Cu2ZnSnS4 (CZTS) MGPs and their effect on the characteristics of MGL solar cells. SEM and EDX studies revealed that the morphology and composition of the formed crystals are influenced by the nature of the flux materials. Structural studies by XRD showed good crystallinities for all MGPs. However, CZTS crystals grown in LiI exhibited a shift of all diffraction peaks towards lower angles and larger lattice parameter values. In addition, powder grown in LiI exhibited the broadest main Raman peak (FWHM = 7.06 cm−1). When CsI was used, the Raman peaks were sharper and narrower with FWHM of 4.5 cm−1, showing a higher level of crystallinity compared to other produced powders. The estimated band gap energy values obtained from EQE measurements were ∼1.57 eV for NaI, KI, RbI, CsI and 1.65 eV for LiI grown CZTS MGPs. The analysis of temperature-dependent current–voltage characteristics indicated that tunneling enhanced interface recombination is the prevailing process in all materials. At low temperatures, the powder crystals grown in LiI, NaI, and RbI revealed the presence of recombination channels that were not observed at room temperature. The MGL solar cell based on CZTS powder grown in CsI resulted in the highest power conversion efficiency of 10.9%.</p&gt

Cu2ZnSnS4 monograin layer solar cells for flexible photovoltaic applications

<h3>Abstract</h3><p>Monograin powder technology is one possible path to developing sustainable, lightweight, flexible, and semi-transparent solar cells, which might be ideal for integration with various building and product elements. In recent years, the main research focus of monograin technology has centered around understanding the synthesis and optoelectronic properties of kesterite-type absorber materials. Among these, Cu2ZnSnS4 (CZTS) stands out as a promising solar cell absorber due to its favorable optical and electrical characteristics. CZTS is particularly appealing as its constituent elements are abundant and non-toxic, and it currently holds the record for highest power conversion efficiency (PCE) among emerging inorganic thin-film PV candidates. Despite its advantages, kesterite solar cells' PCE still falls significantly behind the theoretical maximum efficiency due to the large <i>V</i>OC deficit. This review explores various strategies aimed at improving <i>V</i>OC losses to enhance the overall performance of CZTS monograin layer solar cells. It was found that low-temperature post-annealing of CZTS powders reduced Cu–Zn disordering, increasing <i>E</i>g by ∼100 meV and <i>V</i>OC values; however, achieving the optimal balance between ordered and disordered regions in kesterite materials is crucial for enhancing photovoltaic device performance due to the coexistence of ordered and disordered phases. CZTS alloying with Ag and Cd suppressed non-radiative recombination and increased short-circuit current density. Optimizing Ag content at 1% reduced CuZn antisite defects, but higher Ag levels compensated for acceptor defects, leading to reduced carrier density and decreased solar cell performance. Co-doping with Li and K resulted in an increased bandgap (1.57 eV) and improved <i>V</i>OC, but further optimization is required due to a relatively large difference between measured and theoretical <i>V</i>OC. Heterojunction modifications led to the most effective PCE improvement in CZTS-based solar cells, achieving an overall efficiency of 12.06%.</p&gt

Impact of Li and K co-doping on the optoelectronic properties of CZTS monograin powder

<p>Abstract</p><p>In this work, the impact of Li and K co-doping on the properties of Cu2ZnSnS4 (CZTS) monograin powders used as absorber materials in monograin layer (MGL) solar cells was investigated. CZTS powders were grown in the liquid phase of flux materials with different LiI-KI ratios by synthesis-growth method. According to Atomic Absorption Spectroscopy, the amount of K in the host material did not depend on the molar ratio of LiI to KI in the flux mixtures and remined constant at 0.01 at%. However, the Li concentration depended on the initial amount of LiI in the LiI-KI flux mixture and increased from 0.01 at% to 1.22 at% in the synthesized CZTS. X-ray diffraction, Raman analysis and photoluminescence (PL) analysis confirmed that Li content x = 0.2 and x = 0.4 in the input composition of (Cu1-xLix)1.84Zn1.09Sn0.99S4 resulted in formation of solid solution. The external quantum efficiency measurements showed that the effective bandgap energy of CZTS increased from 1.52 eV to 1.57 eV by increasing the Li content in CZTS from x = 0–0.02 to x = 0.4, respectively. The mean values of VOC of the corresponding monograin layer solar cells increased from 700 to 742 mV. The highest VOC of 784 mV was obtained with device based on solid solution containing 1.22 at% of Li (x = 0.4). The best performing solar cell with power conversion efficiency of 9.4% was obtained with Li and K co-doped CZTS powder (x = 0.002) showing output parameters: VOC = 718 mV, JSC = 20.9 mA/cm2 and FF = 62.5%.</p&gt