The quaternary semiconductor copper zinc tin sulfide (Cu2ZnSnS4, CZTS) is one of the most promising alternatives to Ga and In based semiconductors for thin film solar cells. It consists of non-toxic, cheap, and abundant elements and displays highly beneficial optical as well as electronic properties for photovoltaic applications. In this work we present a solution-based preparation method for CZTS thin films using exclusively metal xanthates as precursor materials. The introduction of branched alkyl side chains (3,3-dimethyl-2-butyl) into the metal xanthates leads to highly soluble precursors with low decomposition temperatures. In addition, these precursors already contain the sulfur needed for the formation of the metal sulfide. Therefore, no external sulfur source such as thiourea, thioacetamide, or elemental sulfur is necessary. For the preparation of CZTS thin films, solutions containing these metal xanthates were used to coat precursor layers, which were subsequently annealed at temperatures between 180 and 350 °C. Depending on the temperature, nanocrystalline films with primary crystallite sizes ranging from 3 nm (180 °C) up to approximately 43 nm (350 °C) were obtained. A combined X-ray diffraction, Raman spectroscopy, and TEM-EDX study showed that a precursor solution with a Cu/(Zn + Sn) ratio of 0.6 has to be used to obtain CZTS films, which show high optical absorption (>2 × 105 cm−1) and an optical band gap of approximately 1.31 eV. First experiments concerning photovoltaic activity of the solution processed CZTS layers were carried out.

We present a thorough study on the various impacts of polymer:nanoparticle ratios on morphology, charge generation and device performance in hybrid solar cells, comprising active layers consisting of a conjugated polymer and in situ prepared copper indium sulfide (CIS) nanoparticles. We conducted morphological studies through transmission electron microscopy and transient absorption measurements to study charge generation in absorber layers with polymer:nanoparticle weight ratios ranging from 1:3 to 1:15. These data are correlated to the characteristic parameters of the prepared solar cells. To gain a deeper understanding of our experimental findings, three-dimensional drift-diffusion-based simulations were performed. Based on elaborate descriptions of the contributions of polymer and nanoparticle phase to device performances, our results suggest that a polymer:CIS volume ratio of 1:2 (weight ratio 1:9) is necessary to obtain a balanced hole and electron percolation. Also at higher CIS loadings the photocurrent remains surprisingly high due to the contribution of the CIS phase to the charge carrier generation.

Tandem solar cells offer the possibility to significantly enhance solar cell performance through harvesting a broader part of the solar spectrum by using complementary absorbing materials. We report on tandem solar cells, with at least one polymer/nanoparticle hybrid layer as absorber material, in which the nanoparticles are prepared in situ by thermal decomposition of metal xanthates directly in the polymer matrix. In a first series, we investigated a hybrid-organic tandem solar cell, with a hybrid solar cell consisting of the silafluorene containing low band gap polymer PSiF-DBT and copper indium sulphide (CIS) nanoparticles as the bottom cell, and a low band gap polymer (PTB7)/fullerene derivative (PC61BM) organic solar cell as the top cell in order to study different recombination layers. Tandem devices with open circuit voltages nearly reaching the sum of the individual cells have been realised. The short circuit current is equal to the value of the hybrid single cell and a fill factor above 50% is obtained, leading to power conversion efficiencies of about 4.1%. Furthermore, the first results on hybrid-hybrid tandem solar cells consisting of two PSiF-DBT/CIS solar cells are presented. Although the preparation of these double hybrid devices is challenging because of the necessity of two thermal annealing steps, the resulting multilayer stack reveals smooth and homogeneous layers with sharp interfaces. The first working hybrid-hybrid tandem solar cells still exhibited 81% of the sum of the open circuit voltages of the single junction solar cells.

In this contribution we present a solution based route toward copper zinc tin sulfide - CZTS - layers using metal dithiocarbamate precursors. We focus on the synthesis of the precursor materials as well as on the fabrication of thin CZTS layers at low temperatures of 350 C and their characterization. Powder Xray diffraction measurements show that a precursor solution containing an excess of the zinc precursor, compared to the Cu and Sn precursors, has to be used to obtain CZTS films without secondary phases. Thus, the prepared films are Zn-rich, which is beneficial for solar cell applications. Raman as well as X-ray photoelectron spectroscopy studies confirm the formation of CTZS. No clear evidence for free ZnS has been found. Electron microscopy shows agglomerates of 10 nm-sized crystallites forming spherical particles with a diameter between 50 rim and 400 nm. The prepared films possess high optical absorption (>1.10(4) cm(-1)) and an optical band gap of approximately 1.6 eV. (C) 2012 Elsevier B.V. All rights reserved.

Nanoparticles capped with amine ligands with different steric properties, dodecylamine and oleylamine, respectively, are investigated in the solid state as well as in solution. A combined X-ray diffraction, small angle X-ray scattering and electron microscopy investigation showed that the nanoparticles exhibit the sphalerite modification of ZnS as crystal phase with a diameter of 3–5 nm. A close packing of the monocrystalline nanoparticles in the solid state is observed. However, in the dodecylamine sample, besides spherical particles, a fraction of the nanoparticles is elongated. The nanoparticles are readily resoluble in apolar solvents like hexane. Dynamic light scattering (DLS) and SAXS investigations of the solutions reveal that the nanoparticles are dissolved as singular particles. In the case of oleylamine-capped ZnS, a defined core–shell structure with a ZnS core with a diameter of 4 nm and an organic shell with a thickness of approximately 2 nm have been found. Dodecylamine-capped nanoparticles slightly tend to form agglomerates with a diameter of approximately 40 nm.

Polymer/copper indium sulfide (CIS) nanocomposite solar cells are prepared via a capper free in situ preparation route using copper and indium xanthates as precursors, which decompose and form CIS nanoparticles in the polymer matrix during a mild thermal treatment. The solar cells generate current in a wide range of the solar spectrum and exhibit efficiencies up to 2.8%. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Copper zinc tin sulfide (Cu2ZnSnS4, CZTS) is a very promising alternative to semiconductors based on Ga or In as solar absorber material. CZTS consists of abundant and cheap elements and in addition it displays very beneficial properties like a high optical absorption coefficient and an ideal band gap for photovoltaic applications. In this contribution, we present the preparation of thin films of copper zinc tin sulfide from metal salts (copper(I) iodide, zinc(II) acetate, and tin(II) chloride) and thioacetamide as sulfur source by a solution-based precursor method. The influence of synthesizing temperatures and concentration of thioacetamide in the precursor solution on the obtained CZTS materials was investigated. X-ray diffraction studies show that kesterite CZTS is formed. Depending on the temperature, nanocrystalline films with primary crystallite sizes from 8 nm (180 degrees C) up to approximately 150 nm (450 degrees C) were obtained. The early stages of the CZTS formation were monitored by time-resolved simultaneous grazing incident small- and wide-angle X-ray scattering (GISAXS, GIWAXS) analysis directly in thin layers revealing that the thermally induced reaction already starts at approximately 105 degrees C. The thin films exhibit high optical absorption (> 1 x 10(4) cm(-1)) and an optical band gap between 1.41 and 1.81 eV depending on the heat treatment. The obtained CZTS materials are of copper-poor and zinc-rich nature, which is ideal for the use in photovoltaic applications.