Effect of Annealing on the Photoelectrochemical Behavior of CuInS₂Nanocrystal Films

Abstract

Photovoltaics based on inorganic thin film absorber layers such as CuInS 2 (CIS) are showing promise in overcoming the increasing energy demand. There are, however, challenges that CIS presents before it can be considered cost effective. A typical synthesis employs a high temperature (∼500 • C) annealing step with a H 2 S atmosphere, which can significantly raise the cost of the photovoltaic devices. In this work we report a relatively low temperature, H 2 S free annealing step (250 • C) that produced a photocurrent enhancement in the CIS nanocrystal film based on the comparison of respective photoelectrochemical measurements. Investigations into the effects of annealing on the morphology, composition, crystallinity and temperature of degradation of the film were carried out. A thin CdS buffer layer can provide photocurrent enhancement of the CIS layer, but it is typically added after annealing because temperatures above 300 • C will degrade optical properties. The low annealing temperature allowed for CIS and the CdS buffer layer to be annealed together, which produced a further photocurrent density enhancement. The combination of a low temperature annealing along with a large photocurrent enhancement of the CIS/CdS bi-layer could help to improve efficiency in the full device fabrication while still keeping costs low.

Controlling Cu2ZnSnS4 photocatalytic ability through alterations in sulfur availability

“…Further, the reaction visually occurs slower, taking twice the time to observe the black color indicative of CZTS formation. This occurs due to the higher decomposition temperature of MPP, which begins around 200 o C[23]. Though the reaction is never heated to temperatures above which MPP decomposes, we clearly see some decomposition in the absence of free-S.…”

Assessing the Band Structure of CuInS2 Nanocrystals and Their Bonding with the Capping Ligand

“…7 The fabrication of efficient CIS solar cells currently requires high temperatures and vacuum methods in a toxic environment, all of which are preventing CIS solar cells from becoming commercially viable. 7,[9][10][11][12][13][14][15][16] Recently, our group has synthesized CIS nanocrystals (NCs) using a one-pot solvothermal method that avoids high-cost and dangerous techniques. [16][17][18] The NCs have been previously characterized photoelectrochemically and structurally.…”

“…7,[9][10][11][12][13][14][15][16] Recently, our group has synthesized CIS nanocrystals (NCs) using a one-pot solvothermal method that avoids high-cost and dangerous techniques. [16][17][18] The NCs have been previously characterized photoelectrochemically and structurally. [17][18] The use of 2-mercapto-5-n-propylpyrimidine (MPP) as a capping ligand in place of the typical oleylamine eliminates the need of thermal removal for the device to produce photocurrent, making it a more cost-effective capping ligand.…”

“…Although the use of gallium and selenium in CIGS adds undesirable costs to the CIGS-based solar cells, they can be removed and replaced, leading to a ternary chalcogenide CuInS 2 (CIS) that is also promising as the light absorber layer in thin film photovoltaics. − CIS has a direct band gap between 1.4 and 1.5 eV and a high absorption coefficient in the range of 10 4 to 10 5 cm –1 . − Solar cells utilizing CIS as the light-absorbing layer are, therefore, good candidates, with an efficiency of >10%, , and >12% in its quasi-ternary counterpart CuIn­(S,Se) . The fabrication of efficient CIS solar cells currently requires high temperatures and vacuum methods in a toxic environment, all of which are preventing CIS solar cells from becoming commercially viable. ,− Recently, our group has synthesized CIS nanocrystals (NCs) using a one-pot solvothermal method that avoids high-cost and dangerous techniques. − The NCs have been previously characterized photoelectrochemically and structurally. , The use of 2-mercapto-5- n -propylpyrimidine (MPP) as a capping ligand in place of the typical oleylamine eliminates the need of thermal removal for the device to produce photocurrent, making it a more cost-effective capping ligand . The interactions of this capping ligand with CIS will be addressed herein.…”

Spin-Coated CZTS Film with a Gradient Cu-Deficient Interfacial Layer for Solar Hydrogen Evolution

“…In these curves, a circular shape indicates high K rec , a semicircular shape means high K tr , and a spiral shape suggests a balance between the two rates. 66,68,69 Comparing the curves, the pure CZTS sample shows a circular response (Figure S15a), while CZTS-8-8-8, CZTS-8-6-6, and CZTS-8-6-4 with the GCD-layer tend toward a spiral shape. CZTS-8-6-6 notably leans more toward a spiral trend, suggesting lower K tr /K rec ratios.…”