Electrodeposition of germanium-containing precursors for Cu2(Sn,Ge)S3 thin film solar cells

Abstract

A B S T R A C TCu 2 (Sn,Ge)S 3 has recently emerged as an absorber layer for single junction thin film solar cells, already achieving power conversion efficiencies of up to 6.7%. Electrodeposition of metallic precursors and their subsequent annealing is an attractive synthesis method for such solar cell absorber layers, since it does not require vacuum conditions and little energy is consumed. The aqueous electrodeposition of metallic germanium based on current knowledge is limited to very thin layers, which do not provide the stoichiometric amount of material required for thick semiconductor layers. Therefore we introduce an electrodeposition method for the growth of germanium-containing precursors for Cu 2 (Sn,Ge)S 3 , using propylene-glycol-based electrolytes. These baths do not require additives, give rates of germanium electrodeposition higher than other plating baths and are cheap. The electrochemical behaviour of copper, tin and germanium in propylene glycol was studied and the corresponding deposits were characterised. Smooth and compact layers of each of the pure elements were deposited. Additionally, the co-electrodeposition of copper and germanium was studied as well and thin films containing the alloy Cu 3 Ge and metallic copper were obtained. A constant [Cu]/[Ge] ratio of around 3 was found over a wide potential range, with a higher plating efficiency than that of pure germanium. For these reasons, copper and germanium were incorporated into the precursor via the referred co-deposition method. After thermal annealing in the presence of elemental sulphur, the semiconductor Cu 2 (Sn,Ge)S 3 was successfully formed and it was incorporated in a working solar cell structure with efficiency of 0.7%

Insight into the Decomposition Mechanism of Donor–Acceptor Complexes of EH2 (E = Ge and Sn) and Access to Germanium Thin Films from Solution

“…Our procedure requires only standard Schlenk techniques and glassware, and any byproducts formed during Ge film deposition can be easily removed by washing with an organic solvent. This is in contrast to pre-existing routes to Ge films that require very high temperatures or sophisticated CVD set-ups . Additionally, we examined four different decomposition pathways for various NHC·EH 2 ·BH 3 (E = Ge and Sn) complexes, and an analysis of the computed Gibbs free energies and kinetic studies points toward the initial E–B bond cleavage as the most likely decomposition route to eventually yield NHC·BH 3 , Ge or Sn, and H 2 .…”

“…A number of different NHCs were investigated experimentally and computationally (Chart ) en route to the isolation of the new reported complexes. Moreover, we show that ImMe 2 ·GeH 2 ·BH 3 (ImMe 2 = (HCNMe) 2 C:) can cleanly deposit germanium as 20 to 70 nm thick films onto various substrates. , While ImMe 2 ·GeH 2 ·BH 3 does not have the required volatility to enable its use in CVD, the use of this complex to yield nanometer-thick Ge coatings via an entirely solution-phase and low-temperature approach has distinct advantages over pre-existing routes to Ge films, including the ability to deposit Ge onto thermally sensitive and nonconducting substrates without the need for high vacuum chambers or electrochemical apparatuses. − In addition to these promising new results, an important question remained unanswered: what is the mechanism of EH 2 release from our donor–acceptor complexes? Does the first step involve LB-E or E-LA bond cleavage, or does a competing process, such as a 1,2-hydrogen shift from the tetrel element (E) to an N -heterocyclic carbene carbon center, occur en route to element deposition?…”

Electrochemical Atomic Layer Deposition (EC-ALD) Low Cost Synthesis of Engineered Materials a Short Review

“…For these reasons, Cu and Ge were incorporated into the precursor via the referred co-deposition method. After thermal annealing in the presence of elemental S, the semiconductor Cu 2 (Sn,Ge)S 3 was successfully formed and it was incorporated in a working solar cell structure with efficiency of 0.7% [82].…”

Fabrication of Cu2Sn1-xGexS3 Thin-Film Solar Cells via Sulfurization of Cu2GeS3/Cu2SnS3 Stacked Precursors

“…Consequently, various compositions and fabrication processes have been reported for CTGS thin-film solar cells, including CTS cells corresponding to x = 0 and CGS thin-film solar cells corresponding to x = 1. As shown in Table 1 [11][12][13][14][15][16][17][18][19][20], a type of CTGS with x = 0 (i.e., CTS), achieved a power conversion efficiency (PCE) of more than 5% [11,12]. PCEs exceeding 5% have also been reported in CTGS solar cells fabricated by alloying Ge with CTS in thin films fabricated by the sulfurization of Ge/Cu-SnS 2 precursors with S and SnS 2 [14] and in thin films obtained by the sulfurization of Cu-Sn metal precursors with S and GeS 2 vapor [15,16].…”