The role of nanoparticle inks in determining the performance of solution processed Cu₂ZnSn(S,Se)₄ thin film solar cells

Abstract

Cu 2 ZnSnS 4 (CZTS) nanoparticle inks synthesized by the injection of metal precursors into a hot surfactant offer an attractive route to the fabrication of Earth-abundant Cu 2 ZnSn(S,Se) 4 (CZTSSe) thin film photovoltaic absorber layers. In this work it is shown that the chemical reaction conditions used to produce CZTS nanoparticle inks have a fundamental influence on the performance of thin film solar cells made by converting the nanoparticles to large CZTSSe grains in a selenium rich atmosphere and subsequent cell completion. The reaction time, temperature and cooling rate of the nanoparticle fabrication process are found to affect doping level, secondary phases and crystal structure respectively. Specifically, prolonging the reaction offers a new route to increase the concentration of acceptor levels in CZTSSe photovoltaic absorbers and results in higher device efficiency through an increase in the open circuit voltage and a reduction in parasitic resistance. Quenching the reaction by rapid cooling introduces a wurtzite crystal structure in the nanoparticles which significantly degrades the device performance, while elevating the reaction temperature of the nanoparticle synthesis introduces a secondary phase Cu 2 SnS 3 in the nanoparticles and results in the highest cell efficiency of 6.26%. This is correlated with increased doping in the CZTSSe absorber and the results demonstrate a route to controlling this parameter.

Solution processing route to Na incorporation in CZTSSe nanoparticle ink solar cells on foil substrate

“…CZTS nanoparticle inks were chemically synthesised using the well-established hot injection of metallic precursors into surfactant and described in detail elsewhere [23]. NaF powder was dissolved in the obtained inks as a novel and effective doping method.…”

Enhanced external quantum efficiency from Cu2ZnSn(S,Se)4 solar cells prepared from nanoparticle inks

“…The CdS buffer layer was deposited using a chemical bath process. 18) After the CdS deposition, the samples were rinsed with deionized water, dried under a nitrogen stream and then annealed at 200°C for 10 min in air. The transparent oxide layer, i-ZnO and ITO were deposited by magnetron sputtering.…”

“…18) To induce grain growth, CZTS nanoparticle thin films were selenized in a tube furnace. The as-deposited precursor thin films were placed inside a cylindrical graphite box with selenium pellets placed directly beneath the substrate.…”

Obtención de estructuras calcopirita (CIGS) y kesterita (CZTS) como absorbentes para dispositivos fotovoltaicos de capa fina mediante métodos de síntesis de bajo coste

“…en diferentes áreas de la celda (̴ 0,5 V) confirma la introducción del azufre (sustitución del Se) en la red cristalina [105,106,116,122,128,135,283,284]. Un alto valor de R S y bajo de R SH disminuye el valor del FF y en consecuencia la eficiencia [285]. Los altos valores de R S están principalmente relacionados con una gruesa interfase de MoS 2 o MoSe 2 y con una reacción incompleta de las nanopartículas [106].…”

“…Además la acumulación de carbón en la parte inferior de la capa absorbente imposibilita la formación de grandes cristales y dificulta la difusión el flujo de corriente a través del dispositivo. Por otro lado, las heterogeneidades como grietas y defectos observados a lo largo de la superficie (Figura 89a) podría dar lugar a un gran número de límites de grano, los cuales están relacionados con valores bajos de R SH a causa de su rol como centros de recombinación [285]. La muestra sulfurizada que utiliza Mo trilayer (C2) no ha mejorado en general los parámetros eléctricos respecto a la muestra monolayer (C1) disminuyendo los parámetros de eficiencia, voltaje y corriente.…”