Impact of Absorber Layer Morphology on Photovoltaic Properties in Solution-Processed Chalcopyrite Solar Cells

Abstract

Solution-processed chalcopyrite solar cells can be economically produced on a large scale; however, for them to be commercially viable, their low efficiency and detrimental processing have to be overcome. To this end, extensive research efforts have been devoted to boost device efficiency and develop benign solution processes. In this review, relevant processes are categorized into molecular-based and particulate-based solution processes, and progress is evaluated in terms of device performance and processing. To identify strategies for improving device performance, the key parameters affecting the optoelectronic properties of the device are discussed. Interestingly, the authors found an unnoticed fact from previously reported experimental results in literature: short-circuit current density increases and deficit of open-circuit voltage decreases as the average domain size of the absorber layer increases. In addition, the power conversion efficiency increases with the grain size irrespective of the band gap, thickness, and processing conditions. Ensuring a large grain size is specifically elucidated to be necessary to increase the photocurrent generation and reduce the charge carrier recombination in the chalcopyrite solar cells. The findings and related reviews afford critical insight into the absorber film design to improve the performance of solution-processed chalcopyrite solar cells.

Over 16% Efficient Solution‐Processed Cu(In,Ga)Se2 Solar Cells via Incorporation of Copper‐Rich Precursor Film

“…Hence, the inferior material quality of the solution process prepared CIGS absorber is responsible for the poor device performance. [11,12] Typically, the solution-processed CIGS thin films exhibit small grains, whereas the vacuum-processed CIGS films present large grains. [13,14] Meanwhile, more defects may exist in the solution-processed CIGS films because of the residual solvent impurities and impurities introduced during film preparation.…”

Toward Understanding Chalcopyrite Solar Cells via Advanced Characterization Techniques

“…Based on the published papers, the correlation between the average grain size of solution‐processed CIGS solar cells and photovoltaic characteristics was obtained. [ 25 ] From the results, J sc increased with average grain size and saturated with further increase in the grain size (Figure 20d). V oc,def decreased with increasing average grain size and power conversion efficiency (PCE) increased with the grain size (Figure 20e,f).…”

“…We previously demonstrated that J sc increases and V oc,def decreases as the grain size increases in solution‐processed CIGS solar cells by analyzing previously reported results. [ 25 ] This indicates that it is important to fabricate high‐quality large‐grained CIGS thin films with few crystal defects prior to controlling the other electrical properties. Because Se vapor is primarily used for selenization in solution‐processed CIGS, processes that produce large grains are required.…”

“…[11][12][13][14][15]17,19,23] However, a performance gap still exists between vacuum-and solution-processed CIGS solar cells, and device efficiency requires further improvement. [25] For this reason, extensive research has been dedicated to tuning the morphology and composition of chalcopyrite.…”

“…Correlation between average gran size and solar cell parameters: d) J sc , e) V oc , and f) PCE. Reproduced with permission [25]. Copyright 2020, American Chemical Society.…”