Supplementary Material
1. Theoretical analyses
We have theoretically analyzed this dynamic process of the space charges,
using a double-layer model. Based on the total current equation,9 the current density j in
the double layers is written as


j   i   i Ei t    0 i


dE
dEi
  s   s Es t    0 s s ,
dt
dt
(S1)
where σi, σi*, εi and Ei(t) are the dark-conductivity, the photo-conductivity, the relative
dielectric constant, and the time t dependence of the uniform electric field, respectively,
in the BL; σs, σs*, εs, and Es(t) express the corresponding quantities in the CSL. The
constant ε0 denotes the vacuum dielectric constant. It is assumed that σs* is much larger
than σi, σi*, and σs, and is time independent. Considering the bias voltage (V = Eidi + Esds)
and the boundary condition εiEi(0)=εsEs(0), we can resolve Eq. (S1), and the
time-dependence of j can be written as
 i 2 s d sV
j t  
e t /  ,
d i  s  d s i 2
(S2)
where τ = ε0(diεs+dsεi)/diσs*. After a time period τ, (1-1/e) of the photogenerated carriers
will be collected by the electrode or accumulated at the BL-CSL interface. The total
t
t
0
0
collected charges in the CSL side electrode can be given by Q(t )   Sj (t )dt  i(t )dt ,
1
where i(t) is the current in the external circuit and S is the effective area of the photocell.
Since the voltage drop across load resistor R is equal to that across the photocell,
 Sj t dt   i(t )dt ,
i (t ) R 
t
t
0
0
(S3)
C
where C is the capacitance of the photocell. Considering that the initial current i(0)=0,
Eq.(3) can be resolved and the external photocurrent is expressed as
i t  
t
t


S  
RC 
e

e
,
  RC  

(1)
where ξ = ε0εi2dsV/di(diεs+dsεi). Therefore, after a rise time τR, namely
t R 
RC 
RCI
ln
,
RCI  

(S5)
with κ = τI = ε0(diεs+dsεi)/diΦ, where I is the light intensity which keeps a constant
during light illumination and Φ is a proportional constant of σs* =ΦI, the largest current
density Jtr0 can be achieved, which is expressed as
J tr
0

 RC 



  RC    
2

RC
RC 
 RC 
1 

 

.
(2)
2. Supplementary Figure
Figure S1 (a) Photoresponses of an ITO/PVDF (1 µm)/ZnPc:C60 (30 nm)/Al photocell
with a light modulation of 1 kHz (31.8 mW/cm2). The slow response is mainly
determined by the large resistance in the circuit (105 Ω), i.e., a large RC time constant
that determines the slow response time which is more easy to detect and simulate.
Another reason comes from the thicker CSL (30 nm) which induces a larger carrier
transit time. Therefore, we studied the response time in a circuit with a smaller RC time
constant and a device with a thinner CSL (20 nm) in Fig 4. (b) A comparison between
the absorption spectra of the blend films (blue curve) and the photocurrent-action
3
spectra of the photocell (red curve). The latter spectra were detected by lock-in
techniques with a 500-W halogen lamp which was employed as light source. The
monochromated light was chopped with a frequency of 17.0 Hz and illuminated to the
transparent ITO electrode. Signals were detected by a two phase lock-in amplifier (NF
Electronic Instruments 5610B). Then the photocurrent-action spectra were normalized
with the photon number. The peaks in these spectra are in agreement, indicating that the
CSL plays a primary role in the production of TPC. It is notable that no signals were
obtained in the ITO/PVDF/Al structure, suggesting that only the CSL was the sensitive
component. In addition, it was found that the relationship between TPC and weak light
intensity exhibits linearity.
4