# Co‐Sensitized Solar Cell Achieves 13.7% Efficiency with Bis‐Hexylthiophene Dyes

## TL;DR

A new solar cell design using organic dyes achieves high efficiency by reducing charge recombination and improving light harvesting.

## Contribution

The study introduces a co-sensitized solar cell with a novel photosensitizer that achieves 13.7% efficiency under full sunlight.

## Key findings

- The solar cell with the H7 photosensitizer achieves a high open-circuit voltage of 1.22 V.
- The co-sensitized device reaches a power conversion efficiency of 13.7% under simulated sunlight.
- The device shows 29.7% efficiency under dim LED light, outperforming perovskite solar cells.

## Abstract

Efficient anti‐aggregation and superb light harvesting in the combination of large and narrow energy gap photosensitizers play a crucial role in suppressing interfacial charge recombination in dye‐sensitized solar cells (DSCs), enabling a high open‐circuit photovoltage (V
oc). Here, two organic photosensitizers, H6 and H7, featuring the bulky donor N‐(2ʹ,4ʹ‐bis(hexyloxy)‐[1,1ʹ‐biphenyl]‐4‐yl)‐2ʹ,4ʹ‐bis(hexyloxy)‐N‐methyl‐[1,1ʹ‐biphenyl]‐4‐amine and N‐(2ʹ,4ʹ‐bis(dodecyloxy)‐[1,1ʹ‐biphenyl]‐4‐yl)‐2ʹ,4ʹ‐bis(dodecyloxy)‐N‐methyl‐[1,1ʹ‐biphenyl]‐4‐amine is reported, respectively, along with bis‐hexylthiophene as the π‐linker and the electron acceptor 4‐(benzo[c][1,2,5]thiadiazol‐4‐yl)benzoic acid. Although the significantly longer alkyl chains do not change the optical energy gap, for H7, it has been able to design molecular structures that exhibit longer excited‐state lifetimes in both dye‐grafted titania and alumina films compared to its H6 counterpart. The copper‐based DSC using the longer alkyl chain‐based photosensitizer H7 achieves a high V
oc of 1.22 V, comparable to the recently explored hybrid methyl ammonium lead‐based perovskite semiconductors (PSK) in solar cells. The co‐sensitized device combined with XY1b results in an efficient DSC with an impressive fill factor of 82.1% and an excellent power conversion efficiency (PCE) of 13.7% under simulated AM1.5 G conditions at 100 mW cm−2. Furthermore, the best device achieves an outstanding efficiency of up to 29.7% under dim light overpassing compared to the PSK solar cells.

The authors demonstrate that the longer excited state lifetime dye in combination with a copper electrolyte produces a high photovoltage of 1.22 V, owing to retarded interfacial charge recombination. The co‐sensitized solar cell achieves efficiencies of 13.7% under full sunlight and 29.7% under LED light.