(Invited) Improved Interfaces in Multilayered Organic-Inorganic Hybrid Solar Cells with π-Conjugated Polymers-Antimony Sulfide-Strontium Titanate-Titanium Oxide

Abstract

We have developed various organic-inorganic hybrid solar cells using Sb 2 S 3 -based composites with π-electronic molecules [1,2]. For examples, utilization of zinc phthalocyanine (ZnPC) for the hybrid solar cell composed of glass/indium-tin-oxide (ITO)/TiO 2 /Sb 2 S 3 /ZnPC/Au achieved long durability with keeping the relative power conversion efficiency ( PCE ) of 90% after the stability test under 1 sun at 63 °C at a relative humidity of 50% for 1,500 h [1]. Using La-decorated Sb 2 S 3 for hybrid solar cell composed of glass/F-doped SnO 2 (FTO)/TiO 2 /La-decorated Sb 2 S 3 /poly[(3-hexylthiophene)-2,5-diyl] (P3HT)/poly[3-(3-carboxypropyl)thiophene-2,5-diyl] (P3CT)/Au resulted in 33% improvement of PCE as compared to that of the non-decorated Sb 2 S 3 because of lowering the resistance at the interface, which was confirmed by the impedance analyses [2]. While doping of Zn into Sb 2 S 3 attained 57% enhancement of PCE . This result is ascribed to the effective lowering the bulk-resistance [2]. In this context, we newly inserted SrTiO 3 layer between TiO 2 and Sb 2 S 3 interface and found the enhancement of the open circuit voltage ( V OC ) from 0.61 V to 0.74 V. Temperature dependence of V OC for SrTiO 3 -inserted device indicated the maximum voltage was 1.7 V, which had been estimated by extrapolation of the line to 0 K. For further improvement of the photovoltaic performance, we modified the thin-film making process for Sb 2 S 3 layer from the previously reported procedures [1,2]. After the spin-coating of the precursor solution of SbCl 3 -thiourea complex in DMF onto the SrTiO 3 layer, heat treatment at 220 °C under vacuum was newly performed. The thickness, surface roughness, and sea-island structure were optimized by their uv-vis measurement, AFM, TEM observations, and current density-voltage ( J - V ) characteristics in terms of transmittance, reflectivity, and short circuit current density ( J SC ) by changing the spin-coating speed, duration of heating, and so on. Through the optimization, remarkable enhancement of J SC from 10.7 mA cm -2 to 13.6 mA cm -2 and improvement of PCE from 4.7% to 6.1% were achieved. [1] A. Hayakawa, M. Yukawa, and T. Sagawa, ECS J. Solid-State Technology , 6 (4) , Q35-Q38 (2017). [2] M. Yukawa, A. Hayakawa, and T. Sagawa, ECS Trans ., 77 (11), 653-659 (2017).