Monolithic DSSC/CIGS tandem solar cell fabricated by a solution process

Sung Hwan Moon, Se Jin Park, Sang Hoon Kim, Min Woo Lee, Jisu Han, Jin Young Kim, Honggon Kim, Yun Jeong Hwang, Doh-Kwon Lee, Byoung Koun Min
2015 Scientific Reports  
Tandem architecture between organic (dye-sensitized solar cell, DSSC) and inorganic (CuInGaSe 2 thin film solar cell, CIGS) single-junction solar cells was constructed particularly based on a solution process. Arc-plasma deposition was employed for the Pt interfacial layer to minimize the damage to the layers of the CIGS bottom cell. Solar cell efficiency of 13% was achieved, which is significant progress from individual single-junction solar cells (e.g., 7.25 and 6.2% for DSSC and CIGS,
more » ... ively). T andem architecture of solar cells, wherein two or more sub-cells with complementary absorption characteristics are stacked and connected either in series or in parallel, is one of the exciting approaches to increase the efficiency effectively of solar cells beyond the Shockley-Queisser limit of single-junction devices 1-3 . For example, dual-and triple-junction solar cells based on III-V compound semiconductor materials such as InGaP/GaAs/InGaAs have been demonstrated to show over 37% power conversion efficiency (PCE) 4 . Moreover, several other photovoltaic materials, including a-Si, CIGS, and various polymers, have also been explored in order to fabricate efficient tandem solar cells 5-8 . In addition to the tandem structure achieved with similar class materials, two substantially different solar cell materials have also been incorporated into tandem solar cell construction. For example, tandem solar cells fabricated with a-Si and a polymer have been demonstrated to show enhanced voltage and power conversion efficiency compared to conventional single-junction solar cells 9-11 . Furthermore, the tandem architecture of a DSSC with GaAs or polymer is reported to show high voltages of 1.8 and 1.36 V, respectively 12,13 . Recently, Liska et al. and Wenger et al. suggested the possibility of a tandem type of architecture with DSSC and CIGS based on mechanical stacking as well as a monolithic conjunction 14,15 . Such a tandem construction of DSSC with CIGS seems to be an ideal design owing to the optical band-gaps of DSSC (,1.7 eV) and CIGS (,1.1 eV), making them suitable for use as top and bottom cells, respectively (see Fig. 1 ). Furthermore, CIGS offers the feasibility of tuning the band-gap by adept control of its composition. This property is particularly beneficial for tandem solar cell applications. For example, by substituting In with Ga and/or Se with S, the band-gap of CIGS can be gradually increased in the range between 1.0 (CuInSe 2 ) and 2.4 eV (CuGaS 2 ) 16 . In addition, from the viewpoint of manufacturing costs, the DSSC/CIGS tandem solar cell would be a competitive option, given the advantage of the economic viability of DSSCs prepared by solution processes. However, to realize a further reduction in the cost of DSSC/CIGS tandem solar cells, it is necessary to develop low-cost and high-throughput solution processing methods (e.g., printing) for the fabrication of the bottom CIGS cell, which is currently fabricated by a vacuum-based method such as co-evaporation. Recently, solution-based fabrication methods for CIGS thin films have attracted much attention due to their potential for realizing low-cost and printable solar cells 17 . The highest efficiencies of solution processed CIGS thin film solar cells have been reported to be 15.2% (hydrazine based) 18 and 12% (non-hydrazine based) 19 . Among the various solution-based synthesis methods, the fabrication of CIGS thin films using nanoparticle ink has potential. This method offers the advantage of fabricating CIGS thin films with uniform and wellcontrolled compositions by starting from stoichiometry-controlled CIGS nanoparticles, thereby eliminating the impurity phases that could significantly deteriorate the device performance 20 . With subsequent sintering of the as-prepared film, the nanoparticles are converted to uniform films of high crystallinity and a large grain OPEN SUBJECT AREAS: SOLAR CELLS TWO-DIMENSIONAL MATERIALS
doi:10.1038/srep08970 pmid:25759191 pmcid:PMC4355678 fatcat:s34is3jay5firaggb22xtbhnci