Relation of Nanostructure and Recombination Dynamics in a Low‐Temperature Solution‐Processed CuInS₂ Nanocrystalline Solar Cell

Abstract

The understanding and control of nanostructures with regard to transport and recombination mechanisms is of key importance in the optimization of the power conversion efficiency (PCE) of solar cells based on inorganic nanocrystals. Here, the transport properties of solution‐processed solar cells are investigated using photo‐CELIV (photogenerated charge carrier extraction by linearly increasing voltage) and transient photovoltage techniques; the solar cells are prepared by an in‐situ formation of CuInS2 nanocrystals (CIS NCs) at the low temperature of 270 °C. Structural and morphological analyses reveal the presence of a metastable CuIn5S8 phase and a disordered morphology in the CuInS2 nanocrytalline films consisting of polycrystalline grains at the nanoscale range. Consistent with the disordered morphology of the CIS NC thin films, the CIS NC devices are characterized by a low carrier mobility. The carrier density dynamic indicates that the recombination kinetics in these devices follows the dispersive bimolecular recombination model and does not fully behave in a diffusion‐controlled manner, as expected by Langevin‐type recombination. The mobility–lifetime product of the charge carriers properly explains the performance of the thin (200 nm) CIS NC solar cell with a high fill‐factor of 64% and a PCE of over 3.5%.

Molecular weight dependent bimolecular recombination in organic solar cells

“…A suppressed, non-Langevin recombination coefficient (with β < β L ) has been reported in organic photovoltaic blends that exhibit high performance. [6][7][8][9][10] Suppressed recombination is desirable to ensure efficient charge extraction. The reduction factor β/β L is a useful "figure of merit" for screening candidate photovoltaic blends to rapidly identify those which are likely to be highly performing.…”

Elucidating the Excited‐State Properties of CuInS2 Nanocrystals upon Phase Transformation: Quasi‐Quantum Dots Versus Bulk Behavior

“…Previous work demonstrated that indiumon-copper-antisites (In Cu ) and copper vacancies (V Cu ) are the dominant donors and acceptor defects, respectively, in ternary chalcopyrite CIS and CISe. [ 16,17 ] Even ordered defect stoichiometries such as CuIn 5 Se 8 or CuIn 5 S 8 may form.…”

ZnO-Based Nanostructuring Strategy Using an Optimized Solution Process in CuInS2 Superstrate Photovoltaics

“…Azimi et al suggested that the organic reagents present in the as-prepared film were removed by the second annealing process. 37 A void surface might help form an interpenetrating heterojunction during the CdS buffer-layer deposition to facilitate effective charge separation at the large area junction; however, in view of our cell configuration (Au/CIS/CdS/ZnO NR/ITO), a porous surface might deteriorate the cell performance because gold electrodes that deeply penetrate the voids in a CIS surface can form shunt paths through direct contact with the CdS buffer layer.…”