All Solution‐Processed Chalcogenide Solar Cells – from Single Functional Layers Towards a 13.8% Efficient CIGS Device

Abstract

Solution processing of inorganic thin fi lms has become an important thrust in material research community because it offers low-cost and high-throughput deposition of various functional coatings and devices. Especially inorganic thin fi lm solar cells -macroelectronic devices that rely on consecutive deposition of layers on large-area rigid and fl exible substrates -could benefi t from solution approaches in order to realize their low-cost nature. This article critically reviews existing deposition approaches of functional layers for chalcogenide solar cells with an extension to other thin fi lm technologies. Only true solutions of readily available metal salts in appropriate solvents are considered without the need of pre-fabricated nanoparticles. By combining three promising approaches, an air-stable Cu(In,Ga)Se 2 thin fi lm solar cell with effi ciency of 13.8% is demonstrated where all constituent layers (except the metal back contact) are processed from solutions. Notably, water is employed as the solvent in all steps, highlighting the potential for safe manufacturing with high utilization rates. remarkable improvements in conversion effi ciency. [ 1 ] The highest effi ciency of 21.0% has been achieved for two thin fi lm technologies so far: Cu(In,Ga)Se 2 (CIGS) [ 2 ] and CdTe. [ 3 ] Remarkably, both CIGS and CdTe records are exceeding the highest value of 20.4% for the market leading polycrystalline silicon wafer technology. Kesterite Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cells are often considered as low-cost alternatives to CIGS and CdTe because they consist of only earth-abundant and nontoxic elements although the effi ciency is currently limited to 12.6% (12.7% not certifi ed). [ 4 ] Well-established dye-sensitized solar cell (DSSC) and amorphous silicon (a-Si) technology peak at 12.3% and 13.4%, respectively. [ 1 ] The most recent boom in TFPV -organometallic halide perovskite cells -has shown an incredible spurt by advancing effi ciency from below 5% to 17.9%(!) within just 3 years. [ 5 ] On the border to classical TFSC is the thin crystalline silicon technology that employs liftoff of 50-micrometer-thick Si wafers to yield up to 21.2%-efficient solar cells. [ 6 ] These massive research and development efforts in the fi eld of TFSC clearly refl ect their commercial value for manufacturing inexpensive effi cient solar modules -rigid or fl exible. Functional layers for the high effi ciency devices are deposited mostly in a batch-to-batch manner using vacuum-based methods such as evaporation, sputtering, or chemical vapor deposition. For example, Figure 1 exhibits a cross-section of a >20% effi cient CIGS solar cell in the so-called substrate confi guration, where 5 out of 6 functional layers are deposited by evaporation or sputtering. In this respect, non-vacuum deposition methods are often promoted as alternative approaches to reduce capital investment costs, offer fast roll-to-roll (R2R) processing and eventually reduce the PV module prices. Particularly desirable among non-vacuum approaches are solutionb...

Transparent Electrodes for Efficient Optoelectronics

“…The reason for this is that the often-used optical transmittance is strongly linked to the reflectance of the transparent electrode, which, in turn, is strongly influenced by the optical properties of the substrate, the film thickness, and the surface texture. In addition, while the transmittance is normally measured on a flat glass substrate, several solar cell absorbers feature textured surfaces (e.g., silicon heterojunction solar cells [1] ) or randomly oriented grains (e.g., CIGS and CZTS [107] ), which increase the roughness of the films and influence the reflectance of the layered stacks. To make an accurate and fair comparison of the amount of light that is parasitically absorbed by a transparent electrode, independent of the substrate and surface roughness, we therefore use the absorptance (A) value, defined as A = 1 -TT -TR, where TT is the total transmittance and TR is the total reflectance.…”

A Bottom‐Up Approach toward All‐Solution‐Processed High‐Efficiency Cu(In,Ga)S2 Photocathodes for Solar Water Splitting

“…[ 6,7 ] The attractiveness of these materials lies in their high extinction coeffi cients, large minority-carrier diffusion lengths (few micrometers), easily tunable band-gap energy (1.0-2.4 eV) by adjusting the alloy composition, and well-positioned conduction band for water photoreduction. In contrast to the PV fi eld-which has focused mainly on the Se-based chalcopyrites-the S-based analogs are better suited to PEC application due to their lower toxicity, the larger relative abundance of sulfur, their improved stability in aqueous electrolytes, and their wider band gap energy.…”

Refractive index and dispersion control of ultrafast laser inscribed waveguides in gallium lanthanum sulphide for near and mid-infrared applications

“…Chalcogenide glasses (ChGs) are an important class of materials used in phase-change memories [1], solar cells [2], sensors [3] and photonics [4]. They contain as their main constituent one or more of the chalcogen elements S, Se and Te, covalently bonded to network formers such as As, Ge, Sb, Ga, Si or P [4,5].…”