Achieving 6.7% Efficiency in P3HT/Indene‐C70 Bisadduct Solar Cells through the Control of Vertical Volume Fraction Distribution and Optimized Regio‐Isomer Ratios. (15th November 2016) - Kutsarov, Dimitar I.
Abstract : Indene C60 and C70 bisadducts (IC60 BA and IC70 BA) have relatively high lowest unoccupied molecular orbital energies. In poly(3‐hexylthiophene) (P3HT)‐based polymer solar cells (PSCs), this produces an increase in open‐circuit voltage ( V OC ) and power conversion efficiency (PCE). However, ICBA synthesis produces a mixture of regio‐isomers with different indene spatial orientations (2, 5, and 12 o'clock) that alter the IC70 BA molecular packing when mixed with P3HT. In this paper, how the IC70 BA regio‐isomerism affects the PSC performance is examined by investigating the molecular packing of P3HT:IC70 BA layers with different regio‐isomeric ratios. For the first time, non‐destructive spectroscopic ellipsometry is used to investigate the effect of the fabrication conditions on the P3HT/IC70 BA vertical volume fraction distribution and the results are attributed to the spatial arrangement of the regio‐isomers. It is demonstrated that this unambiguously affects the PSC performance. As a result, record device efficiencies are repeatedly attained for standard architecture P3HT:IC70 BA PSCs with photoactive areas of 0.43 cm 2, achieving 5.9 (±0.4)% PCE ( n = 15). With control of the IC70 BA constituent, device PCEs vary from below 2.2% to peak values above 6.7%, among the highest recorded PCEs for a P3HT combination, highlighting the importance of the molecular phase separation for high‐efficiency devices. Abstract : A crucial factor to determine the power conversion efficiency of poly(3‐hexylthiophene) (P3HT):indene C70 bisadducts (IC70 BA)‐based polymer solar cells is the variation of the regio‐isomeric ratio of IC70 BA, which affects the molecular packing of the bulk‐heterojunction blend between IC70 BA and P3HT. This is directly related to the device power conversion efficiency, which can vary from below 2.2% to above 6.7%.